AS2.1
Orals: Tue, 25 Apr | Room F2
Like mass and energy, momentum is an extensive quantity and so the momentum of a system is equal to the sum of the momenta of its components. Considering boundary-layer air in the surface-normal ("vertical") direction, its components have momentum in different directions. That of carbon dioxide is downward due to photosynthetic uptake by ecosystems, while those of oxygen and water vapor are upward due to photosynthetic and evaporative sources, respectively. And so on. Importantly, evaporation is several orders of magnitude greater than any other form of surface exchange, and therefore the vertical momentum of air can be precisely approximated by that of water vapor. This allows estimation of the vertical velocity as simply the ratio of the evaporative flux density to the air density, and has important consequences for many aspects of boundary-layer meteorology.
We analyzed atmospheric data from numerous flux towers over a range of climatological and ecological contexts to characterize the vertical velocity and consequent magnitudes of non-diffusive greenhouse gas transport. Our results invalidate long-standing and intuitive attribution of diffusion of some greenhouse gas directly to its sources and sinks, which has neglected the key role of water vapor in diluting the components of dry air.
This work was supported by the projects PID2020-117825GB-C21 (INTEGRATYON3), B-RNM-60-UGR20 (OLEAGEIs) and P18-RT-3629 (ICAERSA) including European Union ERDF funds.
How to cite: Abril-Gago, J. and Kowalski, A. S.: Vertical momentum in the boundary layer and its consequences for transport of greenhouse gases, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8468, https://doi.org/10.5194/egusphere-egu23-8468, 2023.
Measurements collected at two experimental sites, the Amazon Tall Tower Observatory (ATTO) and the tower at the Cuieiras Biological Reserve (ZF2) that was part of the GoAmazon experiment, were considered to study deviations from the law-of-the wall for the roughness sublayer (RSL) above the Amazon Forest. A plethora of physical, chemical, and biological processes are influenced by the flow structure in the RSL. Further, above tall and dense canopies the handshake between the land and the atmosphere in numerical Weather Predictions and Earth Systems Models occurs in the RSL. For the mean velocity, the RSL effects are operationally accommodated using a dimensionless roughness sublayer correction function (φ) to the law-of-the wall. For dense canopies the mixing-layer analogy is assumed, and the correction function φ depends on the vorticity thickness, Ls. φ measures the ratio of the eddy viscosity from attached eddies to a zero-plane displacement (d) and the actual eddy viscosity in the RSL at (z-d), for (z-d)/Ls>>1, φ∼1. However, this formulation remains only plausible for dense forested canopies and its extension to sparse and urban canopies difficult at the least. In the Amazon the experimental determination and modeling of φ may also be challenging for the forest topography that introduce z-dependent mean pressure gradients that then lead to variability in second-order flow velocity statistics with z. In this work an original formulation of φ is proposed based on a scale-wise co-spectral budget model that balances mechanical production to pressure-decorrelation terms in the co-spectral budget. Because the turbulent kinetic energy dissipation rate (ε) is conserved across the vertical velocity spectrum, the co-spectral budget model reveals a novel link between φ and a macro-scale dissipation length, Ld=u*3/ε.The friction velocity, u*, is interpreted from the moving-equilibrium hypothesis to be appropriately defined at the canopy top. The analysis shows that the estimation of φ with the new formulation agrees with independent estimates of φ using measured turbulent momentum flux and mean velocity gradient. Further, Ld emerges as a key length scale in the RSL, being more efficient than the vorticity thickness in the estimation of the peaks of the wind vertical velocity spectra.
How to cite: Mortarini, L., Katul, G., Cava, D., Quaresma Dias-Junior, C., and Chamecki, M.: Law-of-the wall adjustments above the Amazon Forest via Cospectral Budget Model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8231, https://doi.org/10.5194/egusphere-egu23-8231, 2023.
Identifying turbulence regimes in the stable boundary layer (SBL) is not only important for advancing our fundamental understanding of turbulent mixing but is also needed for model-observation intercomparisons and to build meaningful Earth system science models for predicting future climate change in regions subject to weak winds and significant radiative cooling. As a common regime classification, the classic hockey stick curve (Sun et al., 2012) relates the turbulence kinetic energy to the mean horizontal wind speed and differentiates between (1) weak turbulence driven by local shear and (2) strong turbulence driven by the bulk shear separated by a height-dependent threshold. A third (3) intermittent regime marks transitions between the former. However, the effect of thermal stratification on the surface heat fluxes is not directly included in this metric. Here, we explore the recently proposed decoupling metric Ω = LB (z√2)-1 (Peltola et al., 2021) to overcome this limitation as the buoyancy length scale LB ∝ NBV-1 directly incorporates the stratification through the bulk Brunt-Vaisala frequency. Analyzing multi-level observations in persistent polar SBLs, short-lived SBLs over snow and topographically sheltered nocturnal SBLs we found that Ω versus wind speed exhibits an even more clearly pronounced hockey stick behavior with a sudden regime change from (1) to (2), but without the intermittent (3). In contrast to the classic hockey stick metrics, heat fluxes were largest for an intermediate Ω within the strong regime (2) but above the critical threshold velocity. In the SBL, heat fluxes vanished for either very small stratification and, hence, weak gradients, leading to large Ω > 1 in (2), or in (1) as vertical transport is suppressed by the strong stratification. The observations satisfied a simple linear model to predict the threshold Ωcrit from height-dependent wind speed. The latter resembled a classic neutral boundary layer profile with meaningful friction velocities and surface roughness length, suggesting that turbulent transport is coupled to the local surface throughout regime (2). The height-dependence of Ωcrit,however, suggests that z is not the most appropriate vertical length scale in the SBL even for the strong turbulence regime.
References:
Peltola, O., Lapo, K., & Thomas, C. K. (2021). A Physics-Based Universal Indicator for Vertical Decoupling and Mixing Across Canopies Architectures and Dynamic Stabilities. Geophysical Research Letters, 48(5), e2020GL091615. https://doi.org/https://doi.org/10.1029/2020GL091615;
Sun, J., Mahrt, L., Banta, R. M., & Pichugina, Y. L. (2012). Turbulence Regimes and Turbulence Intermittency in the Stable Boundary Layer during CASES-99. Journal of the Atmospheric Sciences, 69(1), 338–351. https://doi.org/10.1175/JAS-D-11-082.1
How to cite: Thomas, C. and Huss, J.-M.: Revisiting the hockey stick curve: exploring an alternative metric for incorporating the role of stratification in distinguishing turbulence regimes in the stable boundary layer, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8626, https://doi.org/10.5194/egusphere-egu23-8626, 2023.
A uniform approximation of flow over gentle hills with a turbulent closure based on mixing length theory is derived. It permits to describe the transition from neutral to stratified flow in the production of mountain drag. Our results corroborate previous studies showing that the transition from the form drag associated to the mountain induced changes in boundary layer friction to the mountain gravity waves drag can be captured by theory. We also confirm that the first is associated with downstream sheltering with relative acceleration at the hill top, the second with upstream blocking with strong downslope winds. We also show that the downslope winds penetrate well into the inner layer. The theory show that the altitude at which the incident flow need to be taken to calculate the drag is related to the inner layer depth at which dissipative effects equilibrate disturbance advection. We also show that the parameter that capture the transition, which in our case is a Richardson number, is directly related to the altitude of the turning levels of the gravity waves with respect to the mountain length. Our uniform solutions are also used to describe the wave field aloft and the distribution of the Reynolds stress in the vertical. Some directions to combine neutral and stratified effects in the parameterization of subgrid scale orographies in large scale models are given.
How to cite: Lott, F., Pauget, L., and Beljaars, A.: Neutral and stratified turbulent boundary layer flow over low mountains, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12869, https://doi.org/10.5194/egusphere-egu23-12869, 2023.
Aerosol-boundary layer interactions play an important role in affecting atmospheric thermodynamics and air pollution. As a key factor in dictating the development of the boundary layer, the entrainment process in the context of aerosol-boundary layer interactions is still poorly understood. Using comprehensive field observations made at a superstation in Beijing, we gain insight into the response of the entrainment process to aerosols. We found that high aerosol loading can significantly suppress the entrainment rate, breaking the conventional linear relationship between sensible heat fluxes and entrainment fluxes. Related to aerosol vertical distributions, aerosol heating effects can alter vertical heat fluxes, leading to a strong interaction between aerosols and the entrainment process in the upper boundary layer. Such aerosol-entrainment coupling can inhibit boundary layer development and explains the great sensitivity of observed entrainment rates to aerosols than can traditional calculations. The notable impact of aerosols on the entrainment process raises holistic thinking about the dynamic framework of the boundary layer in a polluted atmosphere, which may have a significant bearing on the dispersion of air pollutants and the land-atmosphere coupling
How to cite: Li, Z. and Su, T.: PBL-Aerosol-Interactions and Impact on Turbulent Entrainment , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1267, https://doi.org/10.5194/egusphere-egu23-1267, 2023.
Long term observations of shallow convection in the atmospheric boundary layer are rare and difficult to obtain, making it hard to evaluate the capabilities of weather models to accurately represent such features. In this study, we demonstrate that clear air radar reflectivities from insects can be exploited to visualize the horizontal structure of convective cells and rolls over Germany. The patterns observed over a 7 year period are analyzed in terms of their spatial scale, orientation and anisotropy using a two-dimensional wavelet transform. Comparable characteristics can be computed from the near-surface windfields of the convection-permitting regional reanalysis COSMO-REA2. We show that, despite the proximity to the gray zone of turbulence, the reanalysis reproduces a surprisingly realistic diurnal cycle in the spatial patterns and may thus give hints on the wind structures during the unobserved part of the timeseries.
How to cite: Buschow, S. and Friederichs, P.: Climatology of boundary layer wind patterns from clear air radar echoes in Germany, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13532, https://doi.org/10.5194/egusphere-egu23-13532, 2023.
Impact studies of industrial sites for air pollutant emissions must consider all representative meteorological conditions. For low wind conditions, the impact evaluations present large uncertainties. Dispersion mechanisms and turbulence properties in these situations are modified and favor the stagnation of emitted pollutants in the atmosphere. The improvement of the understanding and modeling of these situations is hampered by a lack of data at the international level, particularly for the built environment.
The objectives of this study are to present and analyze experimental data of dispersion of a tracer gas (Helium) under low winds in urban environment, as well as analyze the meteorological conditions corresponding to these situations to characterize the processes dominating the dispersion (especially meandering).
Two measurement campaigns were realized in 2020 and 2022 respectively on the SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique). This built area is located near Paris in a peri-urban environment. The height of the buildings varies between 5 and 30 m. Helium concentrations are measured using air samples and mass spectrometers in real time, in the near field of the emission point (<300m). Wind and turbulence conditions are measured by ultrasonic anemometers positioned at different heights in the surface layer and in the canopy layer. Atmospheric Transfer Coefficients (ATC) are determined to quantify plume dispersion.
Data processing consists in establishing atmospheric turbulence parameters of each experiment (friction velocity, heat flux, Monin-Obukhov Length), in analyzing the spatial distribution of Helium concentrations in the built environment, especially searching correlation between the variations of the concentrations and of the wind directions and making spectral and autocorrelation analysis of the wind speed components to characterize the flow meandering.
The meandering is characterized by an oscillating behavior of the Eulerian autocorrelation function with the presence of a negative loop for the horizontal components u and v of the wind speed. The autocorrelation function of the vertical component w presents a classical exponential curve. The periods of this process vary between 20 and 60 min in the first experimental campaign. The meandering disperses the plume over a wide angular range. The analysis of the time series shows the oscillation of the wind direction in low wind.
The meandering modifies the low frequencies part of the spectrum of the wind speed horizontal components. The impact of the urban environment on this phenomenon is shown using comparisons between spectrum and autocorrelation functions measured at 3 m (inside the buildings canopy) and 30 m heights (above the buildings). The next step is to link the dispersion and meandering processes by performing cospectrum of ATC and wind direction, in order to have information on the frequency dependence of the covariance of these two variables.
How to cite: Bounouas, H., Roupsard, P., Dupont, E., Lefranc, Y., Faucheux, A., Hebert, D., Connan, O., Languionie, P., and Roustan, Y.: Study of atmospheric dispersion under low wind conditions in an urban environment , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17257, https://doi.org/10.5194/egusphere-egu23-17257, 2023.
Vertical temperature profile close to the ground controls many micrometeorological processes. These include development of inversion layer, occurrence of fog, pollution dispersion and vertical transport of heat and moisture. We here present results from an extensive field study, conducted at the observation site next to the north runway at the Kempegowda International Airport, Bengaluru, India (13.208°N, 77.704°E). At the site, we have deployed a HATPRO microwave radiometer, a Windcube Lidar, a set of 4-component radiative flux sensors, a weather station, a 2m mast carrying humidity and temperature sensors for monitoring temperature and humidity, along with a soil temperature profiler and two soil heat flux sensors. With this arrangement at the site, we continuously monitor the vertical profile of temperature, relative and absolute humidity from surface to 10 km height.
Evening transition of the atmospheric boundary layer (ABL) observed during and after the sunset (under calm and clear sky conditions) indicates the development of Lifted Temperature Minimum (LTM) type vertical temperature profiles at the site. Boundary layer cooling observed after the sunset extends more than 200 m from the surface. Cooling is strong near the ground. This leads to formation of penetrative-convection layer close to the ground. Above this unstable convective layer, a stable inversion layer develops that extends to several hundred meters in height.
We will present results from the numerical simulation of the ABL, by initializing from the radiometer observed vertical profile of temperature before sunset. Numerical simulations are based on a high-resolution, one-dimensional radiation model, coupled with ground temperature with and without aerosols' presence. LTM height, intensity, and its evolution with time observed from the field experiments and simulations have been compared and analyzed regarding radiation budget, aerosol property, number density, and soil emissivity. Results presented here indicate that the observed temperature profile in the field experiments matches closely with the simulations only when the presence of aerosols is considered in the numerical simulations. A high concentration of the aerosol in the surface layer, close to the ground enhances the radiative cooling and leads to the formation of the LTM profile.
How to cite: Singh, S. P. and Sreenivas, K.: Role of Aerosol-Induced Radiative Cooling on the Evening Transitions Observed in the Atmospheric Boundary Layer, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-395, https://doi.org/10.5194/egusphere-egu23-395, 2023.
An experimental campaign was organised in summer 2021 in the Eastern Ebro basin, in the frame of the LIAISE Initiative (Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment). Amongst other measurements, the surface energy budget were obtained over different surfaces, including irrigated crops and orchards, rainfed areas and a lake, all them within a radius of 10 km.
For dry weather conditions, the values of the latent heat flux (or Evapotranspiration, ET) were very different depending on the surface, varying from more than 500 W/m2 over an irrigated corn field to less than 30 W/m2 over dry bare soil. These different values implied also different sensible heat fluxes, with the irrigated surfaces showing thermal stable stratification in the afternoon well before sunset due to the cooling effect of evaporation.
The contrast between the irrigated and the rainfed areas is very well-marked induced mesoscale circulations and local transport of humidity, which were overruled by the sea breeze arrival in the afternoon. Over the semi-arid rainfed areas, ET proceeded very irregularly in time and challenged the fundamental hypotesis of stationarity for the computation of the turbulent fluxes. Over all the well-watered surfaces, classical estimates of Potential ET, such as Penman-Monteith or Priestley-Taylor, overestimated the observed values.
How to cite: Cuxart, J., Boone, A., Price, J., Groh, J., and Martínez-Villagrasa, D.: Evapotranspiration: spatial variability in semiarid terrain at the sub-daily scale, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11552, https://doi.org/10.5194/egusphere-egu23-11552, 2023.
In this presentation, a series of projects is presented and discussed to study land-atmosphere (L-A) interaction entirely based on measurements. The first effort, where a suitable sensor synergy was deployed for studying mainly the atmospheric leg, was the Land Atmosphere Feedback Experiment (LAFE) performed in August 2017 at the ARM SGP site. During this campaign, new tools where developed to derive turbulence and flux profiles, investigate flux-gradient relationship, retrieve surface fluxes using machine learning, measure feedback metrics using remote sensing instruments, and compare the observations with nested model simulations down to the turbulent scales. LAFE also demonstrated the importance of advection to investigate local and non-local feedback processes.
The successful performance of LAFE led to the establishment of the Land-Atmosphere Feedback Observatory (LAFO, see https://lafo.uni-hohenheim.de/en) at the University of Hohenheim, Stuttgart, Germany. Here, the LAFE observations are realized operationally so that larger data sets and their statistics can be evaluated. First results on feedback metrics over the heterogeneous agricultural landscape of LAFO will be presented.
These activities culminated in the GEWEX Land-Atmosphere Feedback Observatory (GLAFO), which is one of the projects of the Global Land-Atmosphere System Studies (GLASS) Panel (see https://www.gewex.org/panels/global-landatmosphere-system-study-panel/glass-projects). The GLAFO will observe mass, energy, water, and momentum transport with unprecedented spatial and temporal resolutions, from bedrock to the lower troposphere encompassing the atmospheric boundary layer (ABL). The vision of GLAFO is to establish LAFOs in different climate zones over the Earth in order to study L-A feedback from the diurnal cycle, via seasonal/annual to ideally climatological time scales.
How to cite: Wulfmeyer, V.: Studies of land-atmosphere feedback with a new synergy of observing systems, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11368, https://doi.org/10.5194/egusphere-egu23-11368, 2023.
Observations in the Altiplano region of the Atacama Desert show that the atmospheric boundary layer (ABL) suddenly collapses at noon. This behavior departs from the typical convective ABL normally reproduced by weather and climate models. The collapse occurs simultaneously to the entrance of a thermally driven and topographically enhanced regional flow, characterized by strong winds that produce mechanical turbulence and advect cold air. To identify the main drivers that cause such ABL collapse and the impact on the potential temperature diurnal variability, we use a land-atmosphere coupled model, observations from a comprehensive field campaign, and the Weather and Research Forecasting regional model. We also address the question of how local (surface-atmosphere interactions) and non-local processes (entrainment/ advection/ subsidence) contribute to the surface and ABL dynamics in the region.
A suite of numerical experiments were performed to disentangle the boundary-layer collapse by increasing the level of complexity: from only considering local land-atmosphere interactions to systematically including the non-local contributions of mass advection, cold air advection, and subsidence. Our results show that during the morning the local surface-atmosphere interactions are the dominant contributions and lead to increase the heat exchange that, together with the entrainment processes, warm the atmosphere and allow the ABL to grow. However, this regime abruptly changes at noon and turns into a boundary-layer regime mainly controlled by non-local phenomena. Two interconnected processes lead to a strong decrease of the ABL height (h ): the advection of a shallower boundary layer (~ -250 m h−1 at noon) that causes an immediate decrease of h at midday, and the arrival of a cold air mass which reaches a strength of ~ -3 K h−1 at 1400 LT, strong enough to stop the ABL growth by counteracting the large turbulence levels driven by the high surface fluxes. These two external forcings become dominant over entrainment and surface processes that warm the atmosphere and increase h. As a consequence, the ABL growth is capped during the afternoon. Finally, a wind divergence of ~ 8 x 10−5 s−1 contributes to the collapse by causing subsidence motions that provide additional downward push over the ABL from 1200 LT onward. Without these non-local processes, the ABL would be continuously growing to 3.5 km by the end of the afternoon. Our findings show the relevance of treating large and small processes as a continuum to be able to understand the ABL dynamics and reproduce them adequately in weather and climate models.
How to cite: Aguirre Correa, F., Vilà-Guerau de Arellano, J., Ronda, R., Lobos Roco, F., Suárez, F., and Hartogensis, O.: Midday Boundary-Layer collapse in the Altiplano Desert: the combined effect of Advection and Subsidence, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8816, https://doi.org/10.5194/egusphere-egu23-8816, 2023.
In this work, we will present 4 different approaches to study and visualize the effects of motorway infrastructures such as precast noise barriers or vegetated flat-top earth berms on the dispersion of traffic-related pollutants. The micrometeorological characteristics that directly affect the dispersion of pollutants in the atmosphere were first computed with a pseudo-3-dimensional CFD model by means of the openFoam toolbox. The strengths of this model based on the Reynolds-Averaged Navier–Stokes (RANS) equations with K-ε first-order closure model is to consider the traffic-induced momentum and turbulence (Letaïef et al., 2020). A second approach was to directly visualize the microturbulence from a 1/100 scale model of the motorway cross-section in a wind tunnel. To this end, we refracted the beam of a laser light with a glass rod to observe eddies along a thin plane through a fog generated by a fog machine. Simple shots with a camera can reveal coherent patterns in the chaos. To complete these two models, we conducted two types of field measurements of fine particle concentrations on the studied motorway sector. Direct and indirect measurements were carried out with low-cost microsensors and with environmental magnetism tools applied on dust depositions on accumulating surfaces (Hofman et al., 2017), respectively.
These four approaches indicates similar results. A large recirculation wake region formed on the leeward side of the wall that brings back to the wall the pollutant generated by the traffic is evidenced. On the contrary, flat-top earth berms favor the dispersion of pollutants in the atmosphere. These 4 different approaches allowed us not only to establish these conclusions but also to communicate with all the actors concerned by this study site: scientists specialized in the metrology of atmospheric pollutants, the persons in charge of the motorway company, the elected representatives and the inhabitants of the city where the study site is located.
References:
Hofman, J., Maher, B. A., Muxworthy, A. R., Wuyts, K., Castanheiro, A., and Samson, R.: Biomagnetic Monitoring of Atmospheric Pollution: A Review of Magnetic Signatures from Biological Sensors, Environ Sci Technol, 51, 6648–6664, https://doi.org/10.1021/acs.est.7b00832, 2017.
Letaïef, S., Camps, P., Poidras, T., Nicol, P., Bosch, D., and Pradeau, R.: Biomagnetic monitoring vs. CFD modeling: A real case study of near-source depositions of traffic-related particulate matter along a motorway, Atmosphere, 11, 1–23, https://doi.org/10.3390/atmos11121285, 2020.
How to cite: Camps, P., Poidras, T., Nicol, P., Vittori, M.-A., Letaïef, S., and Lefevre, M.: A multi-approach to study and communicate on the effect of highway infrastructures on the dispersion of traffic-related air pollutants., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10792, https://doi.org/10.5194/egusphere-egu23-10792, 2023.
Concentration fluctuations from continuous small sources in a neutral boundary layer were investigated by mean of high-resolution Large Eddy Simulation (LES). The data set includes concentration moments up to the fourth order and shows the range of validity of the Gamma probability density function (PDF) model for the concentration fluctuations and the transition to a Gaussian PDF for ground sources. We also investigated systematically the off-center line peaks in the concentration variance showing that they are persistent for ground level sources while they disappear according to theoretical arguments for elevated sources. The analysis includes a thorough investigation of the distribution of the most energetic components in the frequency domain by using spectral analysis of the LES results and a stochastic model based on simple theoretical arguments. This analysis supports the picture that the peak in concentration variance frequency distribution is related to both the plume dispersion geometry and the turbulent flow. The results also confirm the recent literature findings that for an elevated source the peak in the concentration variance frequency distribution is almost independent from the crosswind location for a given downwind distance from the source. To our knowledge no previous LES or wind tunnel study had the completeness of the current study.
How to cite: Cassiani, M., Ardeshiri, H., Pisso, I., Salizzoni, P., Marro, M., Stohl, A., Stebel, K., and Park, S.-Y.: Investigation of Concentration Fluctuations for continuous point sources by high resolution Large Eddy Simulation and Stochastic Modeling, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15143, https://doi.org/10.5194/egusphere-egu23-15143, 2023.
The horizontal resolution of numerical weather prediction models (NWP) keeps decreasing towards the hectometric range. However, although topography, land-use, and other static parameters might be better resolved, the performance of physical parameterizations also has to be evaluated and assessed.
One of the most challenging environments for modern NWP models is mountainous topography - namely because, among other issues, turbulence parameterizations were developed for horizontally homogeneous and flat terrain. This assumption is clearly violated in complex terrain, leading to the underestimation of the turbulence kinetic energy and an unrealistic representation of the mountain boundary layer.
In this study, we perform limited-area simulations with the state-of-the-art NWP model ICON (Icosahedral Nonhydrostatic Model) across resolutions (1km, 500m, 250m, 125m) in the Inn Valley, Austria for a day where boundary-layer processes dominate. A thermally-induced valley wind circulation forms on this day, typical for wide valleys. The model is evaluated with observations from the CROSSINN measurement campaign, providing besides the usual meteorological parameters also measurements from LIDAR systems, radiosondes, turbulence eddy-covariance towers, and scintillometers. This data pool of observations allows us to evaluate the current turbulence parameterizations of ICON, starting with the (pre-)operational NWP resolution (1km) across the turbulence grey zone towards large-eddy simulation resolutions (125m). Both the one-dimensional (1D, Mellor-Yamamda type) and the three-dimensional (3D, Smagorinsky closure) turbulence schemes of the model compared with the observations across the grid resolutions to identify the resolution at which the 3D scheme starts to add value over the 1D scheme. Finally, we can check whether further improvements in the turbulence schemes are necessary for the turbulence grey zone.
How to cite: Goger, B. and Dipankar, A.: Evaluating the Turbulence Representation in a Numerical Weather Prediction Model over Mountainous Terrain, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7270, https://doi.org/10.5194/egusphere-egu23-7270, 2023.
The unified parameterization of turbulence and clouds in the atmospheric boundary layer is one of the challenges in current weather and climate models. The updated two-energy turbulence scheme is able to successfully model both stratocumulus cases and shallow convection without the need of an additional parameterization for non-local fluxes. The update includes the introduction of the entropy potential temperature to distinguish between a shallow convection and a stratocumulus regime. In addition, the two-energy scheme is coupled to a simplified assumed PDF method in order to achieve a more universal representation of the cloudy regimes. The updated turbulence scheme has been tuned based on several idealized cases and is now evaluated for several real cases in the ICON modeling framework. These cases include cloud streets over relatively flat terrain and stable boundary layers including fog over complex terrain. The performance of the updated scheme is comparable to or better than the operational setup, and can be thus used instead of the operational turbulence and shallow convection scheme in ICON.
How to cite: Schmidli, J., Bastak Duran, I., Quimbayo-Duarte, J., Sakradzija, M., and Singh, S.: First results of applying the updated two-energies turbulence scheme over complex terrain, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8867, https://doi.org/10.5194/egusphere-egu23-8867, 2023.
Atmospheric boundary layers (ABLs) govern the atmosphere–surface coupling and are therefore of fundamental relevance for Earth’s weather and climate system. Key challenges in modeling and simulation of ABLs arise from the emerging spatio-temporal variability that manifests itself by fluctuating transport processes and intermittency on multiple scales (e.g. [1,2]). Observed flow features are the result of interacting inertial, Coriolis, buoyancy, and viscous forces, acting on all relevant scales of the turbulent flow. Small-scale processes, even if nonuniversal in nature, are usually not resolved due to cost constraints but modeled based on justified physical or empirical relations with the resolved scales, neglecting expensive backscatter (e.g. [3]). This issue is addressed here by a stochastic forward model, the so-called one-dimensional turbulence (ODT) model [4], which allows to preserve small-scale information in a feasible manner. In the ABL, ODT autonomously evolves flow profiles for prescribed initial and boundary conditions. Turbulent advection is modeled by a stochastically sampled sequence of mapping events that punctuate the deterministic advancement of molecular-diffusive processes and Coriolis forces. The model aims to reproduce turbulent cascade phenomenology, resolved along a notional vertically oriented line-of-sight, respecting fundamental physical conservation principles. The dynamical complexity of the model arises from a physically based feedback of the evolving flow state on the stochastic sampling procedure.
In this study, ODT is utilized as standalone tool for the numerical simulation of fluctuating wind velocity and temperature profiles in temporally developing neutral and stably stratified ABLs [5]. Comparison with available reference data shows that the model is able to reasonably reproduce conventional low-order but also detailed flow statistics for fixed model parameters. The model exhibits scale-selective buoyancy damping, but is unable to completely capture the relaminarization under prescribed, but developing, very stable conditions. This can be attributed to the model’s resistance against leaving the fully developed turbulent state. Forthcoming research addresses fluctuations and intermittency effects. For the latter, an event-based clustering approach is presented that aims to identify turbulent cascade events across flow regimes, yielding new possibilities for the analysis and prediction of turbulent time series.
References
[1] L. Mahrt. Annu. Rev. Fluid Mech. 46:23–45, 2014.
[2] V. Boyko, and N. Vercauteren. Boundary-Layer Meteorol. 179:43–72, 2021.
[3] S. S. Zilitinkevich, T. Elperin, N. Kleeorin, I. Rogachevskii, and I. Esau. Boundary-Layer Meteorol. 146:341–373, 2013.
[4] A. R. Kerstein, and S. Wunsch. Boundary-Layer Meteorol. 118:325–356, 2006.
[5] M. Klein, and H. Schmidt. Adv. Sci. Res. 19:117–136, 2022.
How to cite: Klein, M., Schöps, M. S., Medina Méndez, J. A., and Schmidt, H.: Numerical simulation and analysis of transient Ekman boundary layers using a stochastic turbulence model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9116, https://doi.org/10.5194/egusphere-egu23-9116, 2023.
Land-atmosphere feedbacks can play a critical role in daytime convective boundary layer (CBL) evolution. Mixing diagrams provide a framework for disentangling the relative contributions of entrainment, advection, and surface fluxes in the evolution of the CBL moisture and energy budgets. Entrainment is particularly difficult to observe with operational ground-based sensors, and mixing diagrams provide a way to quantify this contribution to the CBL.
We use this framework to evaluate the evolution of the CBL as represented by the Rapid Refresh (which has 13-km grid) and the High-Resolution Rapid Refresh (which has a 3-km grid) numerical weather prediction models. We have identified 30 cases in a three-month period between May and July 2019 at the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) site in north-central Oklahoma; over this period of time the land surface transitioned from a moist soil with green vegetation to a relatively dry soil with harvested crops. A key instrument in this analysis is an infrared spectrometer (IRS), from which profiles of temperature and humidity can be retrieved at 5-min resolution. At this ARM site, a network of IRS and Doppler lidars surround the central facility, from which we are able to derive the advective fluxes of temperature and water vapor. Our analysis focused on how well the two modeling systems represent the relative contributions from entrainment, surface fluxes, and advection over this three-month period.
How to cite: Turner, D. D., Wagner, T., Heus, T., Rosenberger, T., and He, S.: Using Mixing Diagrams to Evaluate the Evolution of theConvective Boundary Layer in NWP Models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17377, https://doi.org/10.5194/egusphere-egu23-17377, 2023.
Accurate modelling of sub-grid momentum flux is crucial for reliable climate simulations of the boundary-layer wind. While first-order momentum flux parametrizations often employed in leading climate models are crude, consisting in a downgradient diffusion scheme with a separate cumulus momentum transport scheme, higher-order turbulence parametrizations which directly prognose the momentum flux are more flexible and general, adhering more closely to the governing equations.
Here, we present the results of studying the sensitivity of the AM4-GFDL global climate simulations of the boundary-layer wind to a first-order, diagnostic, and a higher-order, prognostic, sub-grid momentum flux parametrization. Moreover, we demonstrate how the boundary-layer wind turning angle can be effectively used as a metric to evaluate the impact of changing the sub-grid momentum flux parametrization on the boundary-layer wind structure.
How to cite: Gentile, E. S., Zhao, M., Larson, V., and Zarzycki, C.: Modelling momentum transport in climate simulations of boundary-layer winds with a higher order parameterization scheme , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7255, https://doi.org/10.5194/egusphere-egu23-7255, 2023.
Posters on site: Tue, 25 Apr, 14:00–15:45 | Hall X5
The aim of this study is to investigate whether it is feasible to obtain evaporation estimates from commercial microwave links, which are normally used for telecommunication. These commercial microwave links are already used to monitor path-averaged precipitation by determining the rain-induced attenuation along the link path. The signal transmitted by these microwave links is also perturbed by turbulence during dry periods, which consists of diffraction of the emitted beam by turbulent eddies. This is known as the scintillation effect and special microwave links, called scintillometers, have been designed to measure the full spectral range of the signal intensity fluctuations caused by the scintillation effect and link these fluctuations to the turbulent heat fluxes. However, commercial microwave links are usually sampled at too low temporal resolution to directly capture all the relevant scintillation fluctuations (typically between 0.1 – 100 s). Currently, the links are most often sampled at a temporal resolution of 15 minutes with a recording of the minimum and maximum values, while more recently also “active” forms of sampling with possible intervals up to 1 s have been set up. We intend to investigate what kind of sampling is required to obtain the structure parameter of the refractive index, Cnn, from commercial microwave link data. We will use high resolution sampling rates, which we resample to mimic various commercial sampling strategies. Subsequently, we aim to compute evaporation through deriving the structure parameters for temperature, Ctt, and humidity, Cqq, through a combination with auxiliary data. For this research, we will use data from a dual-beam scintillometer setup, a RPG-MWSC 160 GHz and a Large-Aperture Scintillometer with a 15 cm diameter over a 850 m path over the Ruisdael Observatory at Cabauw, the Netherlands. Additionally, we will install a Nokia Flexihopper 38 GHz, formerly part of a telecom network in the Netherlands, serving as our commercial microwave link. On the measurement site, many other relevant meteorological measurements for studying evaporation (e.g. temperature, humidity, turbulence and energy fluxes) are performed, which we will use as auxiliary and reference data. During this poster session, we would like to present our research plans and invite fellow session participants to join the discussion and give feedback on our ideas.
How to cite: van der Valk, L., Hartogensis, O., Coenders-Gerrits, M., Hut, R., Walraven, B., and Uijlenhoet, R.: Can we measure evaporation using commercial microwave links?, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3500, https://doi.org/10.5194/egusphere-egu23-3500, 2023.
Surface-layer stability is important in many processes, such as the surface energy budget, atmospheric pollution, and boundary-layer parametrization. Most previous studies on stability, however, conducted either theoretical or observational investigations at specific sites, thus leaving a gap with regard to the large-scale pattern. Here, wind speed and temperature observations at multiple heights from the wind-tower network of China are used to estimate the stability during the 2009–2016 period. A series of data-quality-control procedures are conducted and data from 170 wind towers with more than 2 years’ worth of valid observations are selected. The degree of stability is classified by the Obukhov length, which is derived from the wind speed and temperature at 10 m and 70 m above ground level, combined with information regarding the roughness length. Overall, the occurrence frequency of surface-layer instability exhibits significant temporal and spatial variability, being particularly larger in spring and summer than in autumn and winter. The maximum frequency of summertime instability occurs in the time period 1000–1200 local solar time, approximately 2 h earlier than in autumn. Geographically, the peak instability frequency occurs much earlier in the day in north-west China than in other regions, likely owing to the arid and semi-arid land cover. Also noteworthy is the steady increase in instability frequency observed during the period analyzed here, likely resulting from the reduction in the vertical gradient of wind speed. Our findings call for explicit consideration of stability variability in the wind-energy industry and in fundamental boundary-layer investigations in China.
How to cite: Li, J.: Assessing the Surface-Layer Stability over China Using Long-Term Wind-TowerNetwork Observations, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6812, https://doi.org/10.5194/egusphere-egu23-6812, 2023.
The Haituo mountain, one of the main outdoor venues of the Winter Olympic (Paralympic) Games, presents a severe challenge for refined prediction of wind field due to its complex terrain. Therefore, it is imperative to carry out intensive wind field observations to improve our understanding of local circulation characteristics and influence mechanism of complex terrain, and provide data support for the improvement of refined prediction and service in the competition area. Based on data obtained in the observational experiment at Haituo mountain in 2019, the horizontal distribution, vertical structure, mountain-valley wind conversion time and local circulation characteristics under the influences of different background wind fields are statistically analyzed using multi-source data, such as data collected by automatic weather stations, doppler wind lidars, eddy covariance systems, ceilometer and cloud radars, etc. The influence mechanism for local circulation in the Haituo mountain is discussed from three perspectives, i.e., topographic dynamic and thermodynamic impacts and background wind field influences. The results show that the local circulation characteristics in the Haituo mountain are significant under calm weather conditions when the background winds are weak. The local circulation is dominated by thermally-driven valley wind circulation superimposed by the influence of background airflow passing over the mountain. At low-altitude (＜1650 m) stations, mountain and valley winds show opposite directions; at mid- (1650—1800 m) and high- (＞1800 m) altitude stations located near the mountain ridges and peaks, mountain and valley winds both are dominated by westerly winds. Valley wind is significantly stronger than mountain wind at the low- and mid-altitude stations, while the opposite is true at high-altitude stations. In contrast, under the influence of strong background winds, local circulation characteristics disappear and the wind direction in the whole valley tends to be consistent with the background wind, while the difference in wind direction between the daytime and nighttime is small and wind speed decreases with increasing height.
How to cite: Wang, Q.: Local circulation characteristics and mechanism analysis of Haituo mountain in Beijing during winter 2019, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4343, https://doi.org/10.5194/egusphere-egu23-4343, 2023.
Despite the importance of low-level jets (LLJ), their driving mechanisms are not well understood largely due to a shortage of suitable observational data. The classical description for LLJ follows the concept of inertial oscillations at night (NLLJ). Their development is associated with the nocturnal decoupling of winds from the surface friction due to the formation of a near-surface temperature inversion. However, LLJs have also been connected to convectively generated Cold Pools (CP) in kilometre-scale model. CPs are mesoscale areas of cool and dense air formed through convective downdrafts underneath precipitating clouds. Data from the Field Experiment on Submesoscale Spatio-Temporal Variability (FESSTVal) gave us the unique opportunity to test the hypothesis that LLJ formation is also connected to CP passages. We used measurements from three Doppler LIDAR instruments located about 6 km apart from each other, a microwave radiometer and radiosondes for atmospheric profiling, and a large and dense network of surface measurements for the CP detection. During the three-month long field experiment, about 4.7% of all identified LLJ profiles were connected to a CP event (CPLLJ). The average length of CPLLJs was almost two hours. The core of CPLLJ had a mean wind speed of 7 ms−1 and a mean height of 207 m. Using Doppler LIDAR also allowed us to look at wind gusts in the core of the CPLLJs. We measured wind gust of up to 17.5 ms−1 in their core, which exceeds the maximum gust of 15 ms−1 in NLLJs. Close to the surface, the wind speed differences between CPLLJs and NLLJs were even larger than in the core. Most measured CPLLJs appeared at the time of the passage of the CP front and lasted not long after the front has passed, with an interesting exception of a six-hour long CPLLJ during daytime on 29 June 2022. In wind and temperature profiles, we clearly see density currents reaching the experiment site paired with the appearance of strong LLJ profiles. After the passage of the CP front, relatively weaker LLJ profiles were seen. The measurements show that the CP favoured the development of a stably stratified near-surface layer. In a first moment, when the CP front reached the site, there was a mean cooling between the surface up to at least 400 m a.g.l.. After that, the layers bellow 200 m a.g.l. continued to cool, forming a temperature inversion, similar to what one would expect from nocturnal radiative cooling. Radiosondes indicate the typical daytime unstable conditions at the surface and a neutral stratification in the well-mixed boundary layer before the CP arrived. At the time of the CP passage, unstable stratification was seen over a deeper layer followed by the development of a stable stratification in the two hours after the front passed. These conditions led to the formation of a strong and long-lived CPLLJ during daytime. The observations from the FESSTVaL campaign gave first robust evidence that CPs can favour reduced frictional coupling of the wind field to the surface as a prerequisite for generating LLJs.
How to cite: Weide Luiz, E. and Fiedler, S.: Do cold pools generated by convective downdrafts allow the development of low-level jets?, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11526, https://doi.org/10.5194/egusphere-egu23-11526, 2023.
A series of discrepancies between field observations and the traditional thermal energy balance derived from the 1st law of thermodynamics are investigated. Intrigued by some historically known puzzles such as surface energy imbalance, failed potential temperature conservation, and dissimilarity between temperature and humidity, the investigation focuses on physical processes in the atmospheric boundary layer that are uniquely controlled by the diurnal variation of surface heating/cooling. Examination of temperature changes is extended to air-temperature-related variables such as turbulent heat fluxes and temperature variances. Inconsistency between field observations and the traditional thermal energy balance is found not only in their magnitudes but also in their diurnal cycles. Inability of the traditional thermal energy equation for explaining all the observations that are distinctively related to air temperature changes challenges validity of the traditional thermal energy balance theory.
The research is supported by NSF AGS-2203248.
How to cite: Sun, J.: Discrepancies between Boundary-layer Observations and the Traditional Thermal Energy Balance, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1681, https://doi.org/10.5194/egusphere-egu23-1681, 2023.
Filomena snowstorm impacted a large part of the Iberian Peninsula during January 2021, especially affecting the central part of Spain, and covering the Madrid region with up to 50 cm of snow.
In this work, we analyse data from a micrometeorological station (GuMNet-Herrería) placed in a rural environment in the northwest of the Community of Madrid. The objective is to determine the influence of the microscale on the extremely low temperatures reached after Filomena's passage, as well as to better understand the physical processes associated with these extreme conditions.
Although the snowfall lasted only for 2 days, the snow was present on the surface for more than 10 days, already with stable synoptic conditions, accompanied by a weak turbulent transfer between the surface and the lower part of the atmospheric boundary layer. These days after, extremely low temperatures were recorded, reaching minima of up to -26.5 ºC in the central part of the Iberian Peninsula. The presence of snow on the surface modified significantly the components of the surface energy balance (SEB). This included a reduction in the available net radiation at the surface as result of increased albedo and emissivity of the surface, compared to standard conditions (previous period to Filomena), as well as in the turbulent fluxes, contributing to some records of minimum temperatures. The persistence of the snow cover also affected the soil temperatures, keeping the ground heat flux practically constant.
How to cite: Fernández-Castillo, P., Román-Cascón, C., and Yagüe, C.: Influence of the extraordinary Filomena snowstorm on the surface energy balance and its relationship with the subsequent very-low surface temperatures, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5664, https://doi.org/10.5194/egusphere-egu23-5664, 2023.
Air pollution is one of the main hazards for human health worldwide, especially in cities. Surface emissions are the main responsible for the presence of pollutants in the near atmosphere, but meteorological conditions typically play a fundamental role in their accumulation or dispersion. In this work, we focus on the near-surface atmospheric stability and turbulence, for which data from four field campaigns with meteorological and pollutant measurements belonging to the AIRTEC-CM project(*) have been analysed. Available data correspond to the winter and summer seasons of 2020 and 2021 at two public sites located in the city centre of Madrid: a University (ETSII) and a Hospital (HCSC). The evolution of turbulence and stability and their relationships with pollutants such as NO2, PM2,5 and PM10 are investigated. To study turbulence, an analysis of friction velocity and turbulent kinetic velocity is carried out, while the stability parameter (Obukhov length) and the Richardson number obtained by means of the simplified universal similarity functions have been considered for the analysis of the stability. Through the analysis of the mean daily cycle of pollutants, it has been observed how its evolution shows two maxima centered on the morning and evening transitions. The results obtained indicate that pollutant concentrations are strongly influenced by the daily cycle of stability and turbulence, marked by the presence of a maximum of turbulence in the central hours of the day (when the sensible heat flux is greater) and a strong decay of this in the day-night transitions, which in the case of the afternoon transition coincides with the shift from the convective to the stable boundary layer. In addition, the time when this turbulence decay occurs modulates the pollutant concentration values reached, added to the intensity of the stability itself.
(*) AIRTEC-CM research project (S2018/EMT-4329) is funded by The Regional Government of Madrid (Spain) and the European Union.
How to cite: Ortiz-Corral, P., Román-Cascón, C., Serrano, E., Sastre, M., Maqueda, G., and Yagüe, C.: Effects of near-surface atmospheric stability and turbulence on air pollution levels in Madrid , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12568, https://doi.org/10.5194/egusphere-egu23-12568, 2023.
Winds in coastal areas are particularly complex due to the drastic change of roughness and thermal properties between the sea and the land areas. Besides, the coastal topography, the shoreline irregularities, the surface state (land cover/use, soil moisture, sea surface temperature (SST), wind waves), and the interactions with the upper parts of the atmospheric boundary layer (ABL) add more complexity to the final characteristics of the surface winds of these regions.
Among coastal winds, coastal breezes are especially common thermally driven flows formed in mid-latitude regions under fair-weather synoptic conditions. Under these situations, the thermal gradient between the sea and the ocean becomes more important, generating pressure gradient forces that lead to onshore winds during the daytime and offshore during the night. The impacts of these winds are broad and varied: they transport humidity, pollutants, and other physical properties in these regions; they can initiate convection (and even trigger the formation of storms), and they also drive the surface coastal currents, among others. From a societal point of view, the coastal breezes are crucial for the wind power industry, air-quality forecasts, maritime sports, and simply for the refreshing impact they cause, an aspect especially important in some areas commonly affected by extreme maximum temperatures and heat waves. Therefore, a correct understanding of the physical characteristics of the coastal breezes is a needed step to correctly forecast them and to be able to investigate their future trends.
In this work, we present an observational analysis of the coastal breezes observed in the Gulf of Cádiz. We highlight some differences found between the breezes formed at the sea and at the land areas from observational measurements. Besides, we use the mesoscale Weather Research and Forecasting (WRF) model to simulate key case studies, showing how the interaction with the background synoptic wind is very important for the final characteristics that the breezes have. Related to this, we have observed how the effect of the changes in the surface (SST, soil moisture) on the breeze’s characteristics depend on the wind vertical profile (background wind). That is, surface changes impact the ABL mixing and the momentum transfer from higher levels, which seems to be the main mechanism that impact the breezes at lower levels, even more than the surface thermal gradient effect.
How to cite: Román-Cascón, C., Brnas, T., Ortiz-Corral, P., Steeneveld, G.-J., Vázquez, Á., Bruno, M., Izquierdo, A., Reyes, J., Romero, J., Adame, J. A., Sun, J., and Yagüe, C.: Coastal winds in the Gulf of Cádiz (southwestern Iberian Peninsula): insights from observations and models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12826, https://doi.org/10.5194/egusphere-egu23-12826, 2023.
Ecosystems plays a key role on the interaction between the land surface and the atmospheric processes being responsible for strong feedback processes that affect the climate by modifying the relative contribution of the latent and sensible heat to the total energy of the atmospheric air, i.e., the energy partitioning processes. The mechanisms and consequences of this feedback are uncertain and must be studied to evaluate their influence on global climate change.
In this study, our overall objective was to assess the Gross Primary Production (GPP) dynamics and the energy partitioning patterns in three different European forest ecosystems through time series analysis of eddy covariance data. The three contrasted forest types in terms of functioning and climate were an Evergreen Needleleaf Forest in Finland (ENF_FI), a Deciduous Broadleaf Forest in Denmark (DBF_DK), and a Mediterranean Savanna Forest in Spain (SAV_SP). In each site there was and eddy covariance flux tower from which meteorological data, carbon and energy fluxes were analyzed. Firstly, a univariable time series analysis of all variables was made by means of the Buys-Ballot tables, i.e., average year, to study the intra-annual dynamics and then, through the use of the autocorrelation function the interannual dynamics were assessed. Finally, causality of GPP and energy fluxes was studied with Granger causality tests.
Results show that temperature and solar radiation were the main limiting factors in the Northern ecosystems while water availability was determinant for growth in the Mediterranean ecosystem. The autocorrelation function showed that GPP and the meteorological variables in the SAV_SP were more irregular and show lower memory at the long term than at the short one. In addition, this ecosystem presented higher radiation and a larger amount of H+LE, showing the highest Bowen ratio and a lower primary production efficiency in terms of total energy (GPP/(H+LE)). On the contrary, both northern ecosystems showed similar production efficiencies in terms of total energy. However, the DBF_DK showed lower Bowen ratio related to a larger amount of latent heat in relation to sensible heat in associated to the larger plant activity in this forest. Finally, the Granger causality tests showed that the vegetation feedback to the atmosphere was more noticeable in the ENF_FI and the DBF_DK at the short term, influencing latent and sensible heat fluxes.
In conclusion, the impact of the vegetation on the atmosphere influences the energy partitioning in a different way depending on the vegetation type, which makes essential the study of the vegetation dynamics at the local scale to parameterize with more detail these processes and build improved global models.
How to cite: Cicuéndez, V., Litago, J., Sánchez-Girón, V., Román-Cascón, C., Recuero, L., Saénz, C., Yagüe, C., and Palacios-Orueta, A.: Influence of gross primary production in energy partitioning in three different forest ecosystems based on Eddy Covariance time series analysis , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6371, https://doi.org/10.5194/egusphere-egu23-6371, 2023.
There is an urgent need to provide data for greenhouse gases (GHG) monitoring. Flux towers currently represent the most direct approach to provide continuous datasets of surface exchange of these gases. Typically, the flux is derived from the EC method over 30 minutes averaging periods. However, technical and meteorological conditions create gaps with missing or non-reliable data which can represent from 20 % to 60 % of the total period. To compute annual GHG balances, one needs to fill these gaps. Studies on benchmark forest datasets show that gap-filling methods, such as the marginal distribution sampling (MDS), have a good performance on hourly and daily data as well as on annual budgets. This overall setup (EC and MDS gap-filling) is the standard for consolidated datasets over FLUXNET and most flux networks (e.g. Warm Winter 2020 available at www.icos-cp.eu/).
Direct observations are the base of the gap-filling itself and should be praised over gap-filling techniques. More so, the flux community nowadays faces new challenges by moving towards less ideal sites (e.g. European PAUL-ICOS-Cities project to monitor city GHG fluxes), and facing increasing extremes conditions (e.g. Drought-2018, available at www.icos-cp.eu/). In these less conventional frameworks, gap-filling techniques need to be evaluated. Among flux processing techniques, wavelets (WV) can reliably measure non-stationary periods and thus retain more data than standard EC. It does that by resolving flux calculation at sampling rate. For flux measurements it has been most notably used for airborne measurement as it allows computing a flux over short enough periods to attribute the measured flux to a limiter land area.
Here we analyse the CO2 flux over the three consecutive years (2019, 2020 and 2021) in two ICOS sites: FR-Gri, a crop site and FR-Fon a mixed deciduous forest site, both near Paris, France. Results show that from 52 606 data points in FR-Fon, around 50% needed to be gap filled, this includes 11% of missing data and 22% of periods with developed turbulence but non-stationary. Preliminary results for 2019 in FR-Gri show similar ranges. By not requiring stationarity, WV method avoid close to half of the gap filling compared to EC. Comparing 30-minutes-averaged fluxes derived from EC and WV shows good correlation (R²=0.99 for observed data and 0.94 for gap filled data), low root mean square error (RMSE=1.12 for observed data and 1.95 for gap filling). The extra data also decreased continuous gaps, which is expected to improve the performance of gap filling methods. More so, during summer 2019 heatwaves stroke Europe and in particularly French ecosystems. On the flux data, daytime observations during elevated temperatures in 2019 show a WV derived CO2 fluxes closer to zero, suggesting the expected response of stomatal closure during these events. The gap-filled EC data, however, showed relatively unchanged photosynthesis. This study shows the usefulness of using WV computed CO2 fluxes, a result expected to remain valid for longer time series and for other ecosystems and meteorological conditions.
How to cite: Herig Coimbra, P. H., Loubet, B., Laurent, O., Buysse, P., Depuydt, J., Berveiller, D., Delpierre, N., and Mauder, M.: Contribution of wavelets to decrease gap filling in turbulent surface fluxes measurements, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7640, https://doi.org/10.5194/egusphere-egu23-7640, 2023.
The entrainment zone (EZ) capping the convective boundary layer (CBL) is documented using lidar turbulent-scale observations. Sensible and latent heat fluxes have been measured during one hundred hours in CBL temperate and arid regions in free-cloud meteorological conditions. The EZ fluxes have been confronted with scalar gradients, integral scales of turbulence, wind shear, and surface sensible heat flux. In agreement with former observations in stratified surface layer or with EZ large eddy-simulation (LES) studies, Lidar observations show that the buoyant oscillation period associated to the vertical velocity variance are found to be universal relevant parameters for EZ scalar fluxes and gradients. Attempts to introduce non-local CBL scales like the turbulent vertical velocity scale and height, the scalar interfacial layer jumps and the surface sensible heat flux globally increases the scatter of the data. Non-local parametrization particularly failed for EZ latent heat flux compared to sensible heat flux and for weak surface heat flux as it is usually the case in temperate region. Investigating a possible non-local parametrization of EZ vertical velocity variance, it was found that EZ wind shear and then EZ gradient Richardson number play a negligible role. Rather, observations often showed an excess of EZ vertical velocity variance with respect to CBL similarity law that may be explained by a significant contribution of wave-turbulence interaction in the entrainment layer.
How to cite: Gibert, F., Edouart, D., Monnier, P., Collignan, J., Lopez, J., and Cénac, C.: Scalar turbulent flux observations in the entrainment layer and assessment of current parametrizations , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5566, https://doi.org/10.5194/egusphere-egu23-5566, 2023.
The main exchange of energy and mass between the atmosphere and the surface occurs through the means of turbulent processes in the boundary layer of the atmosphere. A modern atmospheric dynamics models use simplified schemes for calculating energy exchange with the surface, based on the Monin-Obukhov similarity theory (MOST). The main requirement of MOST is the uniformity of the underlying surface. This simplification reduces the accuracy of the forecast, especially in regions with complex (heterogeneous) orography, such as in urban conditions. The obtained regularities in the future may allow us to choose the most accurate parameterization for better use of MOST in conditions of a geometrically complex surface and increasing the accuracy of the forecast for urbanized territories.
This paper presents the result of the analysis of the data series for period from 2020 to 2022 obtained from the eddy covariance tower installed in the Meteorological observatory of Moscow State University. Acoustic anemometers with a frequency of 20 Hz record three components of wind speed and acoustic temperature at altitudes of 2.2 m, 11.1 m and 18.8 m. For processing high-frequency mast data and calculating the static characteristics of turbulence, a set of programs implemented by the authors is used. Gaps are filled by a new algorithm proposed in [3].
Based on a long series of measurements, the seasonal and daily variability of heat and momentum fluxes over an urbanized surface was analyzed. The detailed statistical analysis of the influence of eddy structures was carried out on the formation of turbulent fluxes in the city. The method proposed in [2] was used to identify coherent vortices. The method is based on the hypothesis of the relationship of third and second moments, described by the ratio:
where C∼1 is non-dimensional constant, and Sw is skewness of vertical velocity [1]. The compliance of third moments with theoretical values was established for various stratification conditions in 80% of cases. The result indicates a significant contribution of coherent structures to the formation of vertical fluxes over a geometrically complex surface, which is consistent with the estimates received earlier [2, 4].
References
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- [2] Barskov K.V. et al. Two regimes of turbulent fluxes above a frozen small lake surrounded by forest //Boundary-Layer Meteorology. – 2019. – Т. 173. – №. 3. – С. 311-320.
- [3] Drozd I.D. et al. Comparative characteristics of gap filling methods in high-frequency data of micrometeorological measurements //IOP Conference Series: Earth and Environmental Science. – IOP Publishing, 2022. – Т. 1023. – №. 1. – С. 012009.
- [4] Pashkin A.D. et al. An experimental study of atmospheric turbulence characteristics in an urban canyon //IOP Conference Series: Earth and Environmental Science. – IOP Publishing, 2019. – Т. 386. – №. 1. – С. 012035.
How to cite: Drozd, I., Gavrikov, A., Stepanenko, V., Repina, I., Artamonov, A., and Pashkin, A.: Atmospheric turbulence structure above urban heterogeneous surface, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16390, https://doi.org/10.5194/egusphere-egu23-16390, 2023.
The Sichuan Basin (SCB) with complex mountain-basin topography, located immediately to the east of the Tibetan Plateau (TP) in southwest China, is identified as a region with severe PM2.5 pollution over China. To comprehensively understand the SCB terrain effect on the atmospheric environment change, we investigated the effect degree and meteorological mechanism of mountain-valley winds on wintertime PM2.5 in the western SCB, thermally driven mountain-valley winds between the mountains of eastern TP and the western edge of SCB based on near-surface observations of PM2.5 and the ERA5 reanalysis data of meteorology. The results show that the western SCB exhibits a significant diurnal change of mountain-valley winds, shifting between daytime easterly flows and nighttime westerly flows over the western edge of SCB. The frequency of the mountain-valley winds was accounted for 39% of the study’s duration, with the valley and mountain wind-controlling periods being from 2:00 pm to 5:00 pm and 01:00 am to 05:00 am in local time, respectively, and the remaining time being the transition period. Notably, a reduction of 4.5~20.7μg m-3 in near-surface PM2.5 concentrations averaged over the western edge of SCB, decreasing 6~74% in the PM2.5 pollution during the days of mountain-valley winds, which indicates that the mountain-valley winds could alleviate wintertime near-surface PM2.5 in improving air quality over the western SCB. The easterly wind speed was uplifted by 18% during the valley wind-controlling period, corresponding to a 22% reduction in the near-surface PM2.5 levels driven by the mountain-valley winds. The westerly wind speed increased by 50% at the mountain wind-controlling period with a 20% reduction in PM2.5, reflecting the attenuating effect of the favorable atmospheric diffusion conditions on PM2.5 pollution over the western SCB. The daytime noticeably enhanced easterly wind and the strong updraft flows over the eastern slope of TP promoted the dilution and diffusion of air pollutants over the western edge of SCB, and the nocturnal downhill flows along the slope in the westerly winds on the western edge of SCB brought clean TP air to the polluted SCB region in southwest China.
How to cite: Zhang, Y., Zhao, T., Shu, Z., Zhu, Y., Fu, W., and Liang, D.: Attenuation of mountain-valley winds on wintertime PM2.5 change over the western Sichuan Basin, Southwest China, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7929, https://doi.org/10.5194/egusphere-egu23-7929, 2023.
Tomographic 3D reconstructions of artificial puff releases of SO2 were obtained from 2D images taken with UV cameras. These novel 3D reconstructions provide information on the distribution of concentration from a unique experimaental campaign dataset collected in Rena, Norway. The numerical solutions of the inverse problem of obtaining 3D reconstruction form 2D images were addressed with algebraic methods. Preliminary turbulence analysis of the puff concentration pdf, spatial moments, and 2-point statistics are presented. The experimentally obtained concentration pdf of a puff can be compared with different statistical models found in the literature. The time series of the puff spatial moments are obtained from the 3D concentration field directly in relative coordinates from observations. The distance-neighbour function can also be estimated directly from the 3d puff concentrations. The time series of 3D reconstructions of puffs entail promising posibilities for improving physical parametrizations in numerical dispersion models.
How to cite: Pisso, I., Cassiani, M., Kylling, A., Stebel, K., Schmidbauer, N., Stohl, A., Dinger, A. S., Ardeshiri, H., and Park, S.-Y.: Turbulent dispersion of artificial SO2 puffs in the PBL from tomographic reconstructions of the concentration, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16243, https://doi.org/10.5194/egusphere-egu23-16243, 2023.
The response of the lower atmosphere to resolved versus parametrized orographic drag over moderately complex terrain is investigated. Typically, larger terrain scales may trigger propagating gravity waves and generate flow blocking, while the smaller scales (smaller than 5 km) may modify the turbulent atmospheric boundary layer leading to turbulent orographic form drag (TOFD). We perform high-resolution numerical simulations to evaluate the ability of a TOFD parametrization to reproduce the impact of small-scale orographic features on the flow over moderately complex terrain. The tool selected to perform the simulations is the Icosahedral Nonhydrostatic (ICON) numerical model, a unified modelling system for global numerical weather prediction (NWP) and climate studies. In the present study, the model is used in its limited-area and Large Eddy Simulation (LES) modes. In the TOFD parametrization (NWP), the surface stress and the vertical distribution of the resulting momentum flux are formulated in terms of the orography spectrum, meaning that it only depends on the statistical properties of the orography in the box (more specifically, only on the variance of the sub-grid scale orography).
First, the simulations using different grid spacings, from the km scale to the 100 m scale, are evaluated with respect to data collected during the intensive observational period (IOP) of the Perdigão field experiment. The km-scale simulations in NWP mode are run continuously for the complete 49-day IOP using ERA5 data for initial and boundary conditions. The large-eddy simulations, at O(100 m) grid spacing, are run for selected periods nested into the NWP runs. The impact of the resolved orography on the wind field is derived by considering the difference between the high-resolution experiments with high (130 m) and the experiment with low (1 km) resolution orography. This is then compared with the impact of parametrized TOFD, deduced from NWP-resolution experiments with and without TOFD parametrization. The experiments focus on a moderately complex terrain to the north of the Perdigão site, the Serra da Estrela mountain range.
Preliminary results show an important contribution of the TOFD parametrization (in terms of the accumulate TOFD tendency of wind) when the wind flow is aligned perpendicular to the mountain range, which is frequently observed during the second phase of the IOP characterized by weak synoptic conditions. During such periods, the simulation using the TOFD parametrization tends to be closer to the high resolution LES simulation, suggesting that the TOFD parametrization has a net positive effect on the simulations.
How to cite: Quimbayo-Duarte, J., Schmidli, J., Kohler, M., and Schlemmer, L.: Analysis of the wind response to resolved versus parametrized turbulent orographic drag over moderately complex terrain., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11817, https://doi.org/10.5194/egusphere-egu23-11817, 2023.
Inside the Marine Atmospheric Boundary Layer (MABL) turbulence drives a large amount of physical processes through a dynamical coupling. Understanding this coupling is a key issue in weather and climate modeling, but an adapted statistical representation is still lacking. A strong limitation comes from the non-Gaussianities existing inside the MABL. We seek an approach to describe statistically the couplings across scales, which is poorly measured by the power spectrum. Recent developments in data science provide new tools as the Wavelet Scattering Transform (WST), which gives a low-variance statistical description of non-Gaussian processes and offers to go beyond the power spectrum representation.
We proposes to apply WST technique on turbulent moments recorded during the EUREC4A campaign in trade-wind cloud regimes. Using WST analysis on both fluctuating time series and realistic Large-Eddy Simulations (LES), we study how the different scales in turbulent flows interact between each other in the MABL. Are the turbulent flows organised or purely random in the MABL ? Do the couplings change for different cloud organisations ? Do the models show evidence of such scale couplings ?
In this presentation, we first look at the expected WST coefficients law for turbulent flows in the inertial subrange. Second, we present what are the WST coefficients for the measured turbulent moments and how they evolve for different cloud organizations.
How to cite: Gauvrit, E., Bouin, M.-N., Delouis, J.-M., and Boulanger, F.: Unveiling the turbulence scale couplings in fluctuating time series during EUREC4A, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13685, https://doi.org/10.5194/egusphere-egu23-13685, 2023.
Idealised models of convection such as Rayleigh-Bénard convection, horizontal convection etc. have been widely used to study the behaviour of natural fluid systems including but not limited to the atmosphere, the oceans and the flow of lava in the earth's core in a simplified setting 1,2. While such idealised models include only a small subset of the physical processes occurring in nature, their simplified dynamics allows for easier interpretation and study of the interactions of individual physical processes.
In this numerical study, we consider the case of an idealised moist convecting thermal system, with various Dirichlet and Neumann boundary conditions for the temperature and water vapour mixing ratio. The model includes a vertical temperature lapse-rate, the release of latent heat due to the condensation of water vapour and a constant bulk-cooling term to simulate moist convection accompanied by radiative cooling in the earth's atmosphere. This study follows previous studies which have used similar idealised scenarios to understand dry 3 as well as as moist 4 atmospheric convection.
The model is studied for its dynamical response and scaling for varying boundary conditions and input parameters such as the strength of the radiative cooling, the steepness of the lapse rate and the latent heat of condensation to better understand the interaction between moist convection and radiative cooling in the atmosphere. We also compare the convective organisation in our simplified model with more complex cloud-resolving atmospheric simulations 5.
References:
1. G. Ahlers, S. Grossmann, and D. Lohse, “Heat transfer and large scale dynamics in turbulent Rayleigh-Bénard convection,” Reviews of modern physics, vol. 81, no. 2, p. 503, 2009.
2. G. O. Hughes and R. W. Griffiths, “Horizontal convection,” Annu. Rev. Fluid Mech., vol. 40, pp. 185–208, 2008.
3. M. Berlengiero, K. Emanuel, J. Von Hardenberg, A. Provenzale, and E. Spiegel, “Internally cooled convection: a fillip for philip,” Communications in Nonlinear Science and Numerical Simulation, vol. 17, no. 5, pp. 1998–2007, 2012
4. G. K. Vallis, D. J. Parker, and S. M. Tobias, “A simple system for moist convection: the rainy–bénard model,” Journal of Fluid Mechanics, vol. 862, pp. 162–199, 2019
5. C. J. Muller and I. M. Held, “Detailed investigation of the self-aggregation of convection in cloud-resolving simulations,” Journal of the Atmospheric Sciences, vol. 69, no. 8, pp. 2551– 2565, 2012.
Acknowledgement - This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 101034413.
How to cite: Agasthya, L. and Muller, C. J.: Dynamics and scaling of moist, internally cooled convection, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6095, https://doi.org/10.5194/egusphere-egu23-6095, 2023.
Fully developed turbulent flows near walls, regardless of their roughness, are commonly studied based on the law of the wall originally proposed by Prandtl and von Karman in the early part of the 20th century. The derivation of the law of the wall has traditionally been based on theoretical and scaling arguments, under which a balance between dissipation and production (negligible advection terms) of turbulent kinetic energy and a nearly constant shear stress with distance from the wall are assumed in a thin layer of fluid, accommodating about 10% of the boundary layer (i.e., separation of scales). One of the hallmarks of this theory is the von-Karman constant (=0.4) valid across many wall-roughness and boundary layer flow configurations. In many situations, however, the separation of scales required to observe a log-layer is hardly realizable, especially in tall and fully rough canopy flows as in submerged aquatic vegetation and urban centres under certain atmospheric conditions. In recent years, several spectral- and co-spectral -based theories have revealed a "link" between the law of the wall and the energy spectrum of turbulent eddies. This link is exploited here to examine the roughness sublayer of a rough canopy boundary layer. A simplified co- spectral model and data collected from wind tunnel experiments allows to examine the roughness sublayer correction to the law of the wall and test the effect of finite Reynolds number and intermittency on the von-Karman constant, from which the scales dominating the law of the wall in the roughness sublayer are revealed.
How to cite: Bohbot-Raviv, Y. and Katul, G. G.: Perturbed Roughness Sublayer affecting the law of thewall modeled by a "co-spectral link", EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17284, https://doi.org/10.5194/egusphere-egu23-17284, 2023.
The Arctic atmospheric boundary layer (ABL) is a driver of current and future Arctic warming. Yet, the Arctic ABL provides many distinct and nearly idealized cases for investigation. The contrast between polar day and night and the lack of a diurnal cycle and complex topography promotes the formation and observation of persistent ABL states that are usually only short-term in lower latitudes. In 2019 and 2020, the yearlong MOSAiC expedition [1] took place to inject our understanding of the reasons and consequences of current rapid Arctic warming. Its tailor-made combination of atmospheric measurements gathered by the research vessel Polarstern, aircraft, drones, radiosondes, balloons, and various surface-based and remote sensing systems provides us with vast data to analyze.
To ensure MOSAiC data quality and support future data analysis, we apply large-eddy simulations (LESs) for selected weather conditions during MOSAiC, using the PALM model [2] and resolutions of up to less than a meter. Such fine grid spacings allow us to resolve the ship's envelope as an obstacle to the flow and sufficiently represent stably stratified ABLs. PALM's virtual measurement module enables our LESs to create synthetic perturbed and unperturbed observational data. Thus, analysis of their difference and the ship-induced wakes provides an insight into the ship's effects on surrounding in-situ measurements, which is a central aspect for interpreting corresponding data.
Our simulations reveal that effects are not only tied directly to the ship's wake within the turbulent flow. They indicate that ship-induced gravity waves also bear the potential to influence surrounding measurements notably (i. e. their accuracy exceeding). We present and analyze:
- how influences from both sources rely on atmospheric conditions, the measurement positioning, and the considered atmospheric quantity
- that effects notably perturb performed measurements frequently up to more than a kilometer distance
- the underlying mechanisms causing the observed perturbations
- mitigation and interpretation strategies to work with corresponding data
[1] Shupe, M. D. et al. (2022): Overview of the MOSAiC expedition: Atmosphere. Elementa: Science of the Anthropocene. DOI: 10.1525/elementa.2021.00060.
[2] Maronga, B., et al. (2020): Overview of the PALM model system 6.0, Geoscientific Model Development. DOI: 10.5194/gmd-13-1335-2020.
How to cite: Rauterkus, R. and Maronga, B.: Large-eddy simulations analyzing the impact of RV Polarstern on surrounding measurements during MOSAiC, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14855, https://doi.org/10.5194/egusphere-egu23-14855, 2023.
The LES-based PALM model system 6.0 is a state-of-the-art atmospheric numerical model widely used among scientists for urban boundary layer and urban climate studies. Despite being subjected to many validation and sensitivity studies which tested the model’s accuracy and applicability to urban environments, a major step is needed to test its sensitivity to different driving conditions.
In this study, we performed a series of PALM model simulations for a given domain and two selected episodes during the year 2019. Each simulation lasts 72 h, and all of them were performed for an 8 km x 8 km domain in 10 m resolution encompassing a real built-up residential area in the southeast part of the city of Prague, Czech Republic. The simulation setups are identical apart from the initial and boundary conditions imposed. For that purpose we utilized the mesoscale WRF model and created an ensemble consisting of several members with different parameterization schemes.
This study's findings are serving to better understand how different initial and boundary conditions affect the PALM model simulations. In addition, we present the process, complexity, and challenges one can encounter while trying to find the optimal set of initial and boundary conditions for a given PALM model simulation. Moreover, the performed simulations have shown that most of the variance in the ensemble comes from the driving conditions.
How to cite: Radovic, J., Belda, M., Resler, J., Krč, P., Eben, K., Bureš, M., and Geletič, J.: Sensitivity study of the PALM model system to different driving conditions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11730, https://doi.org/10.5194/egusphere-egu23-11730, 2023.
Spring frost has been recognized as the most harmful weather hazard for agriculture. One way to fight it back is using a wind machine - a 6-m diameter blowing fan atop a 10-m mast. It rotates on itself in approximately 4min30s and blows a slightly positive air using the strength of the nocturnal thermal inversion to mix cold air near the ground with warmer air above. Previous studies have focused on the protection area of the wind machine under different weather conditions or propeller designs. However, while weather conditions are undergone and field measurements are sparse, effects like the topography, the synergy between devices, or the addition of a burner are hard to catch and separate and are, therefore, not yet well understood.
In this study, we present field measurements dedicated to the future calibration of a computational fluid dynamics model (PALM) involving an actuator disk to simulate a wind machine operating during radiative frost conditions. This numerical model will aim to understand better such tower's external effects, for which field measurements are challenging to implement.
To characterize the jet of the propeller at the onset, vertical profiles were measured with a 3D sonic anemometer at high frequency (100Hz) 10 m away from the wind machine every meter between 3 and 15 m heights. Mass flow and momentum rates of about 500m3/s and 5000N were deduced for some different designs of wind machines.
To characterize how the jet interacts with the ground regarding the distance from its source, 2D sonic anemometers were placed in a row in front of the wind machine. Results highlight three different zones where the jet behaved distinctively:
- A dead zone, where the jet passed over the ground (0 to 30 m away from the WM);
- An impact zone where the jet directly hit the ground with maximum velocity (40 to 60m away from the WM);
- A spreading zone where the protection mixing was due to eddies spreading in the inter-rows and breaking into smaller eddies in contact with posts and vine plants (70m away from the WM and beyond). As the distance from the machine increased, the jet velocity decreased before vanishing.
From these results about the onset condition and development of the jet, it will be possible to tune the rotating actuator disk to reproduce with PALM (an LES meteorological-oriented modeling system) an acceptable behavior of the flows (gust and weather interacting with the ground) despite several simplifications of the underlying physics.
While calibrations are still ongoing, the first results are encouraging, whether it be on a wind machine in a free environment or with the reproduction of a radiative night situation. The primary analysis will focus on the animation of state variables to assist in analyzing statistical results on field measurements. As little knowledge is available about the combined use of a burner with a wind machine, several strategies for a burner location will be tested in order to initiate a research topic that the authors believe is currently unexplored.
How to cite: Le Cap, C., Carlier, J., Katurji, M., Lin, D., Quénol, H., Georgeault, P., Buisson, E., and Heitz, D.: Towards numerical simulation of a wind machine during spring frost calibrated with field measurements, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1425, https://doi.org/10.5194/egusphere-egu23-1425, 2023.
The planetary boundary layer (PBL) scheme is required in almost all numerical weather prediction and general circulation models to parameterize the vertical diffusion of mass, moisture and momentum, in which the critical bulk Richardson number (Ricr) is a crucial component. This study investigates the sensitivity of the Holtslag and Boville (HB) PBL scheme to the Ricr in the National Centre for Atmospheric Research Community Atmosphere Model version 5 (NCAR-CAM5) over India and its adjoining regions. According to the HB PBL scheme, turbulent motion in the PBL is caused by surface heating because of incoming solar radiation. The simulations were conducted using various values of Ricr (0.19, 0.25, 0.35, and 0.5) as well as the default scheme (Ricr = 0.30) at a horizontal resolution of 1o. A total of five sets of simulations have been conducted, each for six years; the first year was discarded as spin-up time, and the last five years of simulations are considered for the analysis. The study spans DJF (December–January), MAM (March–May), JJA (June–August), and SON (September–November) seasons over the study domain. The study shows that the HB PBL is highly sensitive to the value of Ricr employed in the simulation. The results demonstrate that over the whole study domain (20S-40N, 40E-140E), as well as just over land and ocean, the mean planetary boundary layer height (PBLH) increases nearly linearly with increasing Ricr during all four seasons. The surface sensible and latent heat fluxes exhibit opposite behaviour towards the increment in the values of Ricr. The 2-m temperature, wind, and specific humidity changes are marginal and insignificant during all seasons. Moreover, the total precipitation averaged over the whole domain also shows increasing behaviour as Ricr increases during all four seasons.
Keywords: PBL parameterization, Critical bulk Richardson number, Climate model, Surface turbulent fluxes, Precipitation
How to cite: Namdev, P., Sharan, M., and Mishra, S. K.: Sensitivity of boundary layer parameterization to the critical bulk Richardson number in a climate model over India and its adjoining regions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12270, https://doi.org/10.5194/egusphere-egu23-12270, 2023.
Posters virtual: Tue, 25 Apr, 14:00–15:45 | vHall AS
The Atmospheric Boundary Layer (ABL) has always played a critical role in determining global aerosol dispersion and distribution in the atmosphere. Absorbing aerosols constituting of black carbon (BC) influences our atmosphere in several ways which includes absorption of the incoming solar radiation. There have been several studies on the spatio – temporal heterogeneity of aerosols over the North Eastern Region (NER) of India but very few studies exist on the vertical distribution of aerosols till date. To fill this gap, Microaethalometer (MA), Optical Particle Counter (OPC) and Dr. Pisharoty Radiosonde (sonde) has been deployed using tethered balloon up to 1 kilometre altitude on campaign mode for the first time in NER of India for characterization of airborne aerosols and meteorological parameters. The experiment was conducted successfully over a high altitude station in Meghalaya, Umiam (25.67 oN, 91.91o E, 1040 m amsl) during winter, pre monsoon and post monsoon seasons of the year 2019 and over 3 stations viz., Dhubri (26.02° N, 89.97° E, 31 metres), Guwahati (26.10° N, 91.60° E, 55 metres), and Dibrugarh (27.47° N, 94.91° E, 108 metres) along the Brahmaputra valley in Assam, India during the winter and pre monsoon seasons of the year 2021. Meteorological balloons were also launched simultaneously 4-5 times per day in each of these 3 stations for one day during the time of tethered balloon launch. Distinct diurnal variability has been observed in the vertical profiles of BC and meteorological parameters throughout the day. In the absence of incoming solar radiation or weak turbulence i.e. during the morning, evening and night time the ABL height (ABLH) measured by sonde varied from 75 – 200 m, 50 – 150 m, 100 – 275 m and 50 – 225 m during winter season over Umiam, Dhubri, Guwahati and Dibrugarh respectively. While during pre monsoon season, ABLH varied from 50 – 200 m, 75 – 250 m, 125 – 250 m and 50 to 250 m respectively over the 4 stations. Near surface BC concentration (BCC) was found to be high within the ABL during morning, evening and night time over all the stations. During winter and pre monsoon, maximum BCC reached up to approximately 9 µg/m3, 30.98 µg/m3, 22.16 µg/m3, 13.01 µg/m3 and 5 µg/m3, 9.65 µg/m3, 13.6 µg/m3, 6.4 µg/m3 respectively over Umiam, Dhubri, Guwahati and Dibrugarh near to the surface. ABLH goes above 1 km during day time, where the rapid development of a well mixed vertical profile of BC was observed during the day over the study sites. The vertical profiles of BC also showed multiple elevated layers in some stations which closely followed the vertical profiles of the meteorological parameters.
How to cite: Gogoi, M., Borgohain, A., Kundu, A., Kundu, S. S., Bhuyan, P. K., Pathak, B., Bhuyan, K., Barman, N., Banik, T., Charri, A., Chakravorty, A., Kumar, P., Chanda, R., Raju, P. L. N., Srivastava, A., Gogoi, R. B., and Aggarwal, S. P.: Atmospheric Boundary Layer and the Vertical Distribution of Black Carbon over Plain and Hilly Terrain of North East India using In Situ Measurements, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-350, https://doi.org/10.5194/egusphere-egu23-350, 2023.
Summer Shamal, a strong low-level northwesterly wind in the Middle Eastern region, is the major trigger for dust storm activity with a broad impact on regional transport and human safety. Due to the scarcity of high-frequency data, near-ground turbulent mixing analyses under Shamal are still rare. The current study investigates the near-surface turbulence characteristics of the atmospheric boundary layer (ABL) in the coastal region of Qatar under summer Shamal conditions (26.08 N, 51.36 E). The results show that, in the absence of monsoon, Shamal prevents the development of summer sea breezes in the Persian Gulf. Compared to non-Shamal days (NSD), Shamal days (SD) are characterized by higher sensible heat flux magnitude and turbulent kinetic energy (TKE) with lower humidity, especially around noon time. Turbulence stability analysis indicates the probability of different dust activities during summer SD and NSD. Wind velocity spectra are investigated to evaluate the TKE dissipation rate. A Weibull distribution is observed for PDFs of TKE dissipation rate under SD for both stable and unstable conditions.
How to cite: Li, Y. and Sadr, R.: Atmospheric Turbulent Characteristics under Summer Shamal in Coastal Qatar, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4115, https://doi.org/10.5194/egusphere-egu23-4115, 2023.
The atmospheric stability condition in the coastal region of Qatar are analyzed using the measurements conducted on the shoreline (26.08N, 51.36E). The micrometeorological data are collected, from August 2015 to September 2016, using sonic anemometers (20 Hz) at three heights and a weather station on the top of a 9 m tower. Two different atmospheric daily stability patterns, ‘orderly’ and ‘disheveled’, are identified based on the wind conditions. A day is classified as ‘orderly’ if the amount of wind from the sea lasts less than 10% of the day. Otherwise, a day with an onshore wind of more than 10% is considered ‘disheveled’. The orderly stability pattern shows a daily descending and ascending trend during the sunrise and sunset periods, respectively, while the disheveled days follow a random pattern with no clear order. The probability distribution of the stability parameter shows a narrower distribution for the ‘orderly’ days, containing fewer unstable periods than the ‘disheveled’ days. The chaotic trend during disheveled days could be caused by the inhomogeneity of the roughness between the land and the sea (1000 times). The integral length scales are further investigated to clarify the influence of the local thermally forced flow to the disheveled patterns.
How to cite: Sadr, R. and Li, Y.: Two daily stability patterns in the atmospheric surface layer of the coast of Qatar, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4130, https://doi.org/10.5194/egusphere-egu23-4130, 2023.
The evolution of the Planetary Boundary Layer Height (PBLH) is a very important meteorological parameter because most of the population carries out their socio-economic activities inside this layer and because it has a significant impact on weather events and air quality. This parameter is influenced by energy and mass exchanges between the land surface and the atmosphere. In our study, hourly PBLH data were used over a period of 30 years (1989-2018), for the warm season (May, June, July, August and September). The data we used comes from the ECMWF (European Centre for Medium-Range Weather Forecasts) database, ERA5. By means of Open GrADS (The Grid Analysis and Display System), the PBLH deviations were graphically represented and interpreted. On the other hand, the NAO (The North Atlantic Oscillation) has influences over the climate variability and weather worldwide. It is well known that NAO exhibits considerable variability throughout a season and during a year, as well, and prolonged periods (for a few months) of both positive and negative phases of the pattern are ordinary. Both the PBLH variations and the NAO index can have an impact on the weather and climate conditions. In this study we will present the patterns of PBLH during 1989-2019 and correlations between the NAO index and the variability of the monthly summer PBLH in Moldavia Region, Romania.
How to cite: Cosmina, A., Diana-Corina, B., Adrian, T., Ingrid-Mihaela, M., and Marius-Mihai, C.: Patterns of PBL hight during 1989-2019 over Romania, Moldavia Region using ERA5 data and correlation with NAO index., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9568, https://doi.org/10.5194/egusphere-egu23-9568, 2023.
Fog is a difficult meteorological phenomenon to predict due to its high spatial and temporal variability and the complexity of physical processes and their interplay. In this context, the SOFOG3D field campaign, which took place during winter 2019/2020 over the Landes region in the South-West of France, provides a 3D mapping of the boundary layer during fog events. It aims to advance our understanding of fog processes in order to improve forecasts of fog events by numerical weather prediction (NWP) models.
The present study focuses on three days between 28 and 30 December 2019 characterized by different fog life cycles between two sites about 100 km apart. In situ and remote sensing measurements, such as microwave radiometer and cloud radar, show that on the supersite a radiative fog that occurred the first night lifted into a stratus in the morning remained all day long, and lowered in the afternoon to form a new fog by stratus lowering. In contrast at the Agen site, the stratus completely dissipated and a radiative fog formed the second night. The widespread radiative fog over the entire domain during the first night developed due to cold air advection from the East. We conduct data analysis to study why the stratus lowering is generalized over the northern part of the domain, while the stratus completely dissipates over the southern part of the domain.
This analysis is complemented by a 3D numerical simulation performed with the Meso-NH model applied at 100 m resolution with a downscaling approach from the operational AROME model, using the LIMA 2-moment microphysical scheme with a prognostic representation of a multimodal aerosol population. Preliminary results show that for the second night, the simulation well reproduces the contrasting fog life cycle for both sites with radiative fog on Agen and stratus lowering on the supersite but forming earlier fog on the former.
A budget analysis is conducted to investigate the spatial heterogeneity of this fog event at the regional scale and to study the physical mechanisms involved in fog formed by stratus lowering that remains especially difficult to forecast by NWP models.
How to cite: Fathalli, M., Lac, C., and Burnet, F.: Fog formed by stratus lowering: an observational and modeling case study from the SOFOG3D field campaign, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14885, https://doi.org/10.5194/egusphere-egu23-14885, 2023.
The center of Israel presents relatively simple vertical topographical cross-section: The eastern Mediterranean coast on the west, Judea and Samaria mountain in the center and the deep steep Jordan valley on the east.
To the best of our knowledge, the variability of the boundary layer height (BLH) over Israel during the non-summer period was not investigated. This work presents climatological examination of the daytime BLH variability during non-summer months according to WRF simulations with 3 km horizontal resolution during 5 years. The monthly average BLH above the mountain peak and its easterly slope is found to be lower than that over the coastal area (1-2.5 .vs. 2-3 km) during the winter months, November-February, while during the rest of the year (except March) the situation is reversed.
In order to track the mechanism responsible for the reduction of the BLH over the mountain peak area during winter, an examination of the BLH variability during 10-13 UTC was performed. Accordingly, events with relatively weak pressure gradients and weak (< 5 m/s) easterly flow were found to be responsible for minimal BLH (< 350 m). The synoptic pressure during these events is characterized by ridge from the south in the middle troposphere (500 hPa) and central Red Sea Trough or high to the east or to the north of Israel next to the surface. Fohn winds which locally reduce the humidity and enhance the temperature due to subsidence flow over the eastern slope of the valley and the western slope of the mountain. In such cases, the mild synoptic pressure gradients are responsible for the maintenance of the local cooling over the mountain peak. The advection of hot air to the mountain peak is limited and therefore relatively stable thermal stability is obtained over the mountain peak and its eastern slope.
How to cite: Berkovic, S.: Theoretical examination of non-summer daytime boundary layer height variability over coastal-mountain-valley topography: the case of central Israel, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2014, https://doi.org/10.5194/egusphere-egu23-2014, 2023.
