AS1.10
Orals: Tue, 25 Apr | Room 1.85/86
High ice water content (HIWC) regions with small ice crystals, where ice water contents (IWCs) are greater than 1.5 g m-3 and median mass diameters (MMDs) less than about 300 micrometers, occur above tropical mesoscale convective systems (MCSs) and can have detrimental impacts on aircraft engines. Data collected by the French Falcon aircraft and the National Research Council of Canada Convair-580 during the 2014 and 2015 High Altitude Ice Crystals and High Ice Water Content (HAIC/HIWC) projects are revisited here along with coordinated modeling studies to investigate processes that can produce such HIWCs. In particular, data collected from 2014 in the vicinity of Darwin Australia and from 2015 in the vicinity of Cayenne French Guyana are used to determine how bulk microphysical properties (e.g., number concentration, IWC, median volume diameter) and characteristics of ice crystal size distributions (i.e., multimodal nature, parameters fit to gamma distributions for each mode) vary with environmental conditions such as temperature, vertical velocity, MCS age, distance from MCS core, and surface characteristics. It is determined that temperature and vertical velocity are the biggest controls of small ice crystals, but younger cells, stronger convective strengths and closer proximity to convective cores also increase the relative importance of small crystals.
Numerical simulations conducted using the Weather Research and Forecasting model with four different bulk microphysics schemes generally reproduce the observed temperature, dew-point, and wind structure. However, comparison of regime-specific observations against properties simulated over Cayenne using a variety of existing parameterization schemes show that although the coverage and evolution of convection is well predicted, simulations overestimate the intensity and spatial extent of observed airborne X-band radar reflectivity and do not well depict the peak of observed size distributions with maximum dimensions between 0.1 and 1 mm. To explore formation mechanisms for large numbers of small ice crystals, a series of simulations varying the representation of secondary ice production (SIP) processes were conducted. Simulations including one of three SIP mechanisms separately (i.e., the Hallett–Mossop mechanism, fragmentation during ice–ice collisions, and shattering of freezing droplets) did not replicate the observed ratio of number concentration divided by IWC. However, the simulation including all three SIP processes produced HIWC regions consistent with observations in terms of number concentration and radar reflectivity, which was not replicated using the original P3 two-ice category configuration that only included the Hallett-Mossop mechanism. In summary, observations and simulations show primary ice production plays a key role in generating HIWC regions at temperatures < -40 Celsius, shattering of freezing droplets dominates ice particle production in HIWC regions between -15 and 0 Celsius during the early stage of convection, and fragmentation during ice–ice collisions dominates between -15 and 0 Celsius during the later stage of convection and between -40 and -20 Celsius over the whole convection period. This study thus shows the dominant role of SIP processes in the formation of numerous small crystals in HIWC regions. Implications for future measurement and modeling needs are discussed.
How to cite: McFarquhar, G., Huang, Y., Hu, Y., Brechner, P., Korolev, A., Morrison, H., Milbrandt, J., Wolde, M., Nguyen, C., and Protat, A.: Observational and Modeling Studies of High Ice Water Content Clouds: Implications for Process–Oriented Understanding, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-22, https://doi.org/10.5194/egusphere-egu23-22, 2023.
The HIAPER Cloud Radar (HCR) is a 94 GHz W-band radar deployed in an underwing pod on the NCAR HIAPER aircraft. We use dual polarized Doppler observations collected in three major field campaigns:
- The Cloud Systems Evolution in the Trades (CSET) study focused on the characterization of the cloud fields in the stratocumulus and the fair-weather cumulus regimes within the subtropical easterlies over the northern Pacific.
- Motivated by challenges in their modeling, Southern Ocean clouds were observed south of Tasmania during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES).
- Deep convective clouds in a tropical environment were the focus in the Organization of Tropical East Pacific Convection (OTREC) field campaign.
In this study we classify clouds sampled by HCR in these very different environments into twelve categories, based on the clouds’ convective and stratiform characteristics. We calculate dimensional and convective properties of the clouds in the different categories and contrast and compare derived statistics. We analyze updraft regions observed in all cloud categories, their dimensions and velocities. Characteristics of precipitation shafts from the precipitating clouds, such as precipitation fraction or strength are also provided.
How to cite: Romatschke, U.: Cloud properties from airborne radar observations collected in field campaigns, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2868, https://doi.org/10.5194/egusphere-egu23-2868, 2023.
Tropical Tropopause Layer clouds have a significant impact on the Earth's radiative budget and regulate the amount of water vapor entering the stratosphere. They are a key component of the climate system but their observation is still challenging. The Strateole-2 project aims at a better understanding of dynamical, transport, and processes in the Tropical Tropopause Layer (TTL) using long-duration super-pressure balloons flying for several months in the lower stratosphere along the equator belt. From October 2021 to late January 2022, three microlidars flew onboard stratospheric balloons, slowly drifting just a few kilometers above the clouds. These observations have unprecedented sensitivity to thin cirrus and provide a fine scale description of cloudy structures both in time and space. Statistical comparisons with spaceborne lidar CALIOP are discussed, highlighting the unique ability of the microlidar to detect optically thin clouds. The modulation of outgoing longwave radiation by tropical clouds is also investigated using the balloon-borne observations.
How to cite: Lesigne, T., Ravetta, F., Podglajen, A., Tran, D., Bureau, J., Mariage, V., Pelon, J., and Hauchecorne, A.: Characterization of Tropical Tropopause Layer clouds combining balloon-borne and space-borne observations, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7035, https://doi.org/10.5194/egusphere-egu23-7035, 2023.
Cirrus in mid latitudes (<= 60° N) are often affected by aviation and pollution while cirrus in high latitudes (> 60° N) develop in a more pristine atmosphere. In this study, we compare the microphysical properties of cirrus measured in mid latitudes and cirrus measured in high latitudes. The analyzed properties are: the ice crystal number concentration (N), effective diameter (ED) and ice water content (IWC) of cirrus from in situ measurements during the CIRRUS-HL campaign in June and July 2021. We use a combination of cloud probes covering ice crystals sizes between 2 and 6400 µm. The differences in cirrus properties are investigated with dependence on altitude and latitude and we show that there exist differences between mid-latitude and high-latitude cirrus. An increase in ED and a reduction in N is observed in high-latitude cirrus compared to mid-latitude cirrus.
In order to investigate the cirrus properties in relation to the region of formation, we also combine our measurements with 10-day backward trajectories to identify the location of cirrus formation and the cirrus type: in situ or liquid origin cirrus. According to the latitude of cloud formation and latitude of the measurement, we classify the cirrus in three groups: cirrus formed and measured at mid latitudes (M-M), cirrus formed at mid latitudes and measured at high latitudes (M-H) and cirrus formed and measured at high latitudes (H-H). This analysis shows that part of the cirrus measured at high latitudes are actually formed at mid latitudes and therefore influenced by mid-latitude air masses. We discuss the differences of the cirrus properties under this new classification. Our study helps to advance the understanding of upper-tropospheric cirrus properties at mid and high latitudes in summer and the influence of anthropogenic perturbations.
How to cite: De La Torre Castro, E., Jurkat-Witschas, T., Afchine, A., Hahn, V., Kirschler, S., Krämer, M., Lucke, J., Spelten, N., Wernli, H., Zöger, M., and Voigt, C.: Differences in microphysical properties of cirrus at high and mid latitudes from airborne measurements, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15602, https://doi.org/10.5194/egusphere-egu23-15602, 2023.
Mixed-phase clouds are essential elements in Earth’s weather and climate system. Atmospheric observation of mixed-phase clouds occasionally demonstrated a strong discrepancy between the ice particle and ice nucleating particle number concentration of several orders of magnitude at modest supercooling [1, 4, 6]. Various secondary ice production (SIP) mechanisms have been hypothesized which can increase the ice particle number concentration by multiplication of primary ice particles [2, 3].
In this study, we focus on SIP as a result of droplet-ice collisions, commonly known as rime-splintering or Hallett-Mossop (HM) process. During riming supercooled droplets collide with an ice particle and freeze upon impact and lead to the formation of secondary ice particles. Our main objectives are to quantify the number of secondary ice particles and to learn more about the underlying physics. Therefore, we conducted laboratory experiments at IDEFIX (Ice Droplets splintEring on FreezIng eXperiment) in which small droplets collide with a fixed ice particle of 1 mm in diameter. IDEFIX is designed to simulate atmospheric relevant conditions regarding temperature, humidity, impact velocities and collision rates. The riming process was observed with high-speed video microscopy and infrared thermography to visualize the growing rimer structures and the surface temperature of the riming ice particle, respectively. Further, the secondary ice particles were counted via inertial impaction on a supercooled sugar solution in the ice counting device (cut off diameter of 2 µm) developed at IMK-AAF, KIT.
The following parameters were investigated: the air temperature was varied between -4°C and -10°C, the ice-droplet impact velocities were set either to 1 ms-1 or 3 ms-1, and the lognormal droplet size distribution was adjusted to have the mode diameter between 18 µm and 30 µm with the standard deviation between 1.6 µm and 8.4 µm. Under these conditions, the collisions rates between droplets and rimer were between 102 and 103 mm-1s-1 , as determined from the video records and with a rimer heat balance model [5] using measured surface temperature as input data. Thus, the simulated riming process is typical for convective clouds; both dry and wet growth could be realized in IDEFIX. We found no efficient and reproducible secondary ice production during riming within the range of the investigated parameters. The amount of secondary ice particles produced in all our experiments was well below the values expected from the HM mechanism [3, 7], where several hundreds of secondary ice particles per mg rime were found at optimal conditions. Six potential SIP cases (out of 31) could be identified where ice was detected in the ice counting device. Four of them could be attributed to rime spicules break-off due to sublimation.
[1] Crosier, J., et al. 2011, DOI: 10.5194/acp-11-257-2011.
[2] Field, P.R., et al. 2016, DOI: 10.1175/amsmonographs-d-16-0014.1.
[3] Korolev, A. and T. Leisner 2020, DOI: 10.5194/acp-20-11767-2020.
[4] Luke, E.P., et al. 2021, DOI: 10.1073/pnas.2021387118.
[5] Pruppacher, H.R. and J.D. Klett, Microphysics of Clouds and Precipitation. 2010, Springer Dordrecht.
[6] Taylor, J.W., et al. 2016, DOI: 10.5194/acp-16-799-2016.
How to cite: Hartmann, S., Seidel, J., Keinert, A., Kiselev, A., Leisner, T., and Stratmann, F.: Secondary ice production - No evidence of a productive rime-splintering mechanisms during dry and wet growth, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11199, https://doi.org/10.5194/egusphere-egu23-11199, 2023.
Ice crystal formation and growth processes in mixed-phase clouds (MPCs) are not sufficiently understood leading to uncertainties of atmospheric models in representing MPCs. One of these processes is riming, which occurs when liquid water droplets freeze onto ice crystals. Riming plays a key role in precipitation formation in MPCs by efficiently converting liquid cloud water into ice. However, riming is challenging to observe directly and there are only few studies quantifying riming in Arctic MPCs.
In this study, we derive the normalized rime mass 𝑀 to quantify riming. We use airborne data collected during the (AC)3 field campaign HALO-(AC)3 performed in 2022. For this campaign, two aircraft were flying in formation collecting closely spatially collocated and almost simultaneous in situ and remote sensing observations. We aim to quantify 𝑀 by two methods. First, we present an Optimal Estimation algorithm to retrieve 𝑀 from measured radar reflectivities. We find 𝑀 by matching measured with simulated radar reflectivities 𝑍𝑒obtained from in situ particle number concentration observations. As forward operators, we use the Passive and Active Microwave radiative TRAnsfer tool (PAMTRA) and empirical relationships of 𝑀 and particle properties. The latter are derived via aggregation and riming model calculations. Second, we derive 𝑀 from in situ measured particle shape. We calculate the complexity 𝜒 of in situ measured particles, which relates particle perimeter to area. We then derive 𝑀 from empirical relationships that were again obtained from synthetic particles. We compare the obtained 𝑀 derived by both methods and evaluate the occurrence of riming in terms of meteorological conditions and macrophysical cloud properties to understand external drivers and variability of riming. This will lead to a better understanding of riming and thereby helps to improve modelling of this important arctic MPC process.
How to cite: Maherndl, N., Maahn, M., Moser, M., Lucke, J., Mech, M., and Risse, N.: Airborne observations of riming in arctic mixed-phase clouds during HALO-(AC)3, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5000, https://doi.org/10.5194/egusphere-egu23-5000, 2023.
A new CALIPSO satellite retrieval for cirrus clouds has been developed over the last 1.5 years that retrieves ice particle number concentration, effective diameter, and ice water content. It compares favorably with in situ measurements from many field campaigns around the world. This talk would briefly describe the new method targeting single-layer cirrus clouds and focus on new findings resulting from this retrieval, relating them to climate model predictions. These results indicate that there are two types or categories of cirrus clouds. Type 1 cirrus appear to form through heterogeneous ice nucleation (het), have visible optical depths < 0.3, and are most abundant; they are what most people visualize as a “cirrus cloud”. Type 2 cirrus may form through a combination of het and homogeneous ice nucleation, have visible optical depths > 0.3 (with visible extinction coefficients typically 4 times greater than type 1 cirrus), and are often associated with warm fronts, orographic gravity waves, and other lifting processes. However, type 2 cirrus clouds constitute 76% to 88% (depending on latitude) of the estimated net cloud radiative effect of all cirrus clouds. Based on comparisons between retrieved and predicted ice particle number concentrations and effective diameters, these type 2 cirrus clouds are poorly represented in climate models, possibly partly due to the predicted dependence of ice nucleation on layer-average pre-existing ice (not realistic near cloud top where ice nucleation occurs). Predicted ice nuclei concentrations may also need revising.
How to cite: Mitchell, D. and Garnier, A.: Characterizing two types of cirrus clouds that differ in nucleation mechanism and radiative effect, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16885, https://doi.org/10.5194/egusphere-egu23-16885, 2023.
In recent years our understanding of cirrus cloud processes has been significantly advanced. However, a large uncertainty regarding the influence of cirrus formation mechanisms on the microphysical properties, and hence radiative properties of cirrus clouds still remains. This leads to uncertainty in global climate models and climate change projections. In this work we aim to identify different cirrus formation regimes and analyze their influence on cirrus microphysical properties. We combine DARDAR-Nice satellite observations with Lagrangian back trajectories of meteorological and aerosol reanalysis data on the Northern Hemisphere. Our goal is to classify observed cirrus clouds by means of their trajectories and investigate the trajectories' influence on observed cirrus microphysical properties. With our data-driven nested clustering approach we identify different meteorological regimes that lead to cirrus formation. We are also able to isolate the effect of dust ice nucleating particle (INP) exposure along the trajectory from meteorological variability.
We identify four different meteorological clusters that lead to characteristic cirrus cloud microphysical properties and can be associated with liquid origin and in-situ formed cirrus clouds. Furthermore, we find that dust concentrations in cirrus cloud back trajectories are significantly higher compared to cloud free trajectories with comparable meteorological conditions. This indicates the importance of dust acting as INP during heterogeneous nucleation. The magnitude of the dust concentration, however, has only a negligible effect on cirrus microphysical properties.
How to cite: Jeggle, K., Neubauer, D., and Lohmann, U.: Identification of cirrus formation regimes using cluster analysis of back trajectories and satellite data, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5002, https://doi.org/10.5194/egusphere-egu23-5002, 2023.
Ice cloud and floating snow play critical roles in Earth’s energy budget and hydrological cycle. Their diurnal variation is tightly coupled with convection development life cycle, hence it also greatly impacts the diurnal cycle of surface precipitation and top of the atmosphere radiation. Due to the high degree of freedom of ice crystal microphysical properties, remote sensing of ice/snow cloud is challenging for passive spaceborne sensors.
In this work, we present a global diurnal ice/snow cloud product by merging three spaceborne passive microwave sensor observations together (GPM-GMI, NPP-ATMS, and MT-SAPHIR). This dataset includes ice water path (cloud ice + falling snow), cloud top height (CTH) and cloud bottom height (CBH) at pixel level between 2015 – 2016, and monthly gridded values at 2deg X 2deg X 2 hours grid scale. The convolutional neural network (CNN) approach is adopted for the algorithm development by learning from collocated CloudSat observations, and the Monte Carlo dropout method is used for uncertainty estimation. A customized loss-function is developed to retrieve cloud mask and mass together.
We evaluated the retrieval at collocated pixels as well as against other independent field campaign and ground-based measurements. Diurnal and semi-diurnal distributions of the IWP will be presented. We will also demonstrate how we use this product to evaluate model performance on capturing the general distribution and diurnal variation of the frozen hydrometeors in the atmosphere.
How to cite: Gong, J., Wang, C., Wu, D., Wang, Y., Ding, L., and Barahona, D.: A Global Merged Diurnal Ice/Snow Cloud Product from Spaceborne Passive Microwave Observations and Its Applications to Model Evaluation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8660, https://doi.org/10.5194/egusphere-egu23-8660, 2023.
The cloud thermodynamic phase (ice / mixed-phase / liquid) is a crucial parameter to understand the earth radiation budget, hydrological cycle and atmospheric thermodynamic processes. The phase partitioning of clouds and their parameterization in global climate models have therefore become of particular interest.
To improve our understanding of the frequency of occurrence and temporal evolution of cloud phase, geostationary passive sensors can be very useful due to their wide field of regard and high temporal resolution. However, the retrieval of cloud phase using passive instruments is challenging since the spectral signature of the phase is weak compared to other parameters of the clouds and atmosphere. Especially the distinction between ice and mixed-phase clouds is difficult and previous efforts to retrieve cloud phase often only distinguished between ice and liquid phase.
We present a new method to detect clouds and retrieve their phase using the passive instrument SEVIRI aboard the geostationary satellite Meteosat Second Generation. The method uses probabilities derived from active observations (the Lidar-Radar product DARDAR) of cloud top phase. Combining these probabilities for different SEVIRI channels gives probabilities for the presence of a cloud and for its cloud top phase. Our probabilistic approach includes a measure of uncertainty and allows us to distinguish between ice, mixed-phase, supercooled liquid, and warm liquid clouds. The method is tested against active satellite measurements and shows good agreement. Finally, we discuss its advantages and limitations. In the future, we plan to use our method to study the microphysical (such as optical thickness and effective radii) and macrophysical (such as temporal evolution and extent) properties of ice and mixed-phase clouds.
How to cite: Mayer, J., Bugliaro, L., Ewald, F., and Voigt, C.: A probabilistic approach to determine the thermodynamic cloud phase using passive satellites, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13062, https://doi.org/10.5194/egusphere-egu23-13062, 2023.
The large cirrus outflows that arise from deep convection play a vital role in modulating the energy balance of the Earth’s atmosphere. One important question is how much do the initial conditions of the deep convection influence the subsequent evolution of the detrained cirrus, and if these initial conditions are important, over what timescales do they matter? Characterising how these cirrus outflows evolve over their entire lifetime, and how they might change in response to anthropogenic emissions is important in order to understand their role in the climate system and to constrain past and future climate change.
Building on the ‘Time Since Convection’ product used in Horner & Gryspeerdt (2023), this work investigates how the initial conditions of the deep convection influence the subsequent evolution of the detrained cirrus- in particular, how does the timing, location, and meteorological environment of the deep convection alter the detrained cirrus, and for how long are these initial conditions important for the cirrus properties- is there a ‘memory’ of the initial conditions of the deep convection imprinted on the properties of the cirrus hours or days after the initial deep convection has dissipated? To answer this question, data from the DARDAR, ISCCP, and CERES products are used to build a composite picture of the radiative and microphysical properties of the clouds, which is investigated under varying initial conditions.
The initial state of the convection is found to have a considerable impact on cirrus development under a variety of conditions. The diurnal cycle, particularly the timing of the convection, is a strong control on the cloud radiative effect, particularly in regions of strong convective activity. The initial aerosol perturbation is also shown to play a role in cirrus development, both in the large scale properties of the cirrus and the microphysical properties.
This demonstrates a potential time dependent impact of aerosol and convection on cloud properties and provides a template for future studies of cloud development incorporating diverse sets of measurements.
How to cite: Horner, G. and Gryspeerdt, E.: Do detrained cirrus clouds have memory of the deep convection they came from?, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15307, https://doi.org/10.5194/egusphere-egu23-15307, 2023.
The most common type of cloud in the Arctic latitudes is mixed-phase stratocumulus. These clouds play a critical role in the Arctic energy budget. Previous observations in the central (north of 80° N) Arctic have shown a high occurrence of prolonged periods of a shallow, single-layer mixed-phase stratocumulus at the top of the boundary layer (altitudes ~300-400m). However, recent observations from the summer of 2018 showed a prevalence of a two-layer boundary-layer cloud system. Here we use large-eddy simulation to examine the maintenance of one of the cloud systems observed in 2018 as well as the sensitivity of the cloud layers to different micro- and macro-scale parameters. We find that the model generally reproduces the observed thermodynamic structure well, with two near-neutrally stratified layers in the boundary layer caused by a low cloud (located within the first few hundred meters) capped by a lower temperature inversion, and an upper cloud layer (based around one kilometer or slightly higher) capped by the main temperature inversion of the boundary layer. The investigated cloud structure is persistent unless there are low aerosol number concentrations (<5 cm-3), which cause the upper cloud layer to dissipate, or high large-scale wind speeds (>8.5 m s-1), which erode the lower inversion and the related cloud layer. These types of changes in cloud structure led to a substantial reduction of the net longwave radiation at the surface due to a lower emissivity or higher altitude of the remaining cloud layer. The findings highlight the importance of better understanding and representing aerosol sources and sinks over the central Arctic Ocean. Furthermore, they underline the significance of meteorological parameters, such as the large-scale wind speed, for maintaining the two-layer boundary-layer cloud structure encountered in the lower atmosphere of the central Arctic.
How to cite: Ekman, A. M. L., Bulatovic, I., Savre, J., Tjernström, M., and Leck, C.: Large-eddy simulation of a two-layer boundary-layer cloud system from the Arctic Ocean 2018 expedition, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11386, https://doi.org/10.5194/egusphere-egu23-11386, 2023.
Recent experiments and modelling studies suggest that secondary ice production (SIP) may close the gap between observed Arctic ice nucleating particle (INP) concentrations and ice crystal number concentrations (Ni). Here we explore model sensitivities with respect to the complexity of different INP parameterisations in numerical simulations under the premiss that Ni is governed by SIP. Idealised, cloud-resolving simulations are performed for the marine cold air outbreak cloud deck sampled during M-PACE (cloud-top temperature of -17°C) with the ICOsahedral Nonhydrostatic (ICON) model.
Droplet shattering (DS) of rain drops according to Phillips et al. (2018), and collisional breakup (CB) (Phillips et al. 2017) were implemented and tested in addition to the existing Hallet-Mossop (HM) rime splintering implemented in ICON’s state-of-the-art two-moment bulk microphysics scheme. Furthermore, a fully prognostic temperature-dependent budget representation of INP (Solomon et al. 2015) was implemented and contrasted to a less sophisticated time-relaxation formulation of atmospheric INP concentrations.
Overall, 16 different model experiments (24h runs) were performed and analysed. Despite the considerable amount of uncertainty remaining with regard to ice production mechanisms and their process representation in numerical models we conclude from these experiments that: (i) Ni-enhancement through SIP can close the gap between measured and simulated Ni concentrations during M-PACE in ICON consistent with previous studies (e.g. Sotiropoulou et al. 2020; Zhao et al. 2021), (ii) only simulations where DS dominates the SIP signal (potentially amplified by CB) capture the vertical Ni in-cloud profile correctly, (iii) INP recycling remains necessary for MPC maintenance during M-PACE even if Ni is dominated by SIP, and (iv) experiments using a computationally more efficient relaxation-based prognostic parameterisation of primary nucleation are statistically invariant from simulations considering a prognostic INP budget.
How to cite: Possner, A., Pfannkuch, K., and Ramadoss, V.: Interplay between Primary and Secondary Ice Production (SIP) in Arctic Mixed-Phase Clouds (MPCs) as simulated for the M-PACE campaign in ICON, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6658, https://doi.org/10.5194/egusphere-egu23-6658, 2023.
Ice multiplication processes have been recognized to play an important role in the forming of cloud ice crystals, and multiple mechanisms have been proposed to describe ice multiplication. Ice multiplication processes have been investigated for a variety of cloud types, but mostly for stratiform clouds or shallow cumulus, which do not reach temperatures of homogeneous freezing. In this study, sensitivity experiments are performed to study the role of ice multiplication in the developing stages of deep convective clouds. A double-moment cloud physics scheme was adopted. Except as the default Hallett-Mossop rime splintering process, two additional ice multiplication processes, which are droplet shattering during the freezing of supercooled drops and the collisional breakup of ice particles, are implemented. Moreover, two different parameterization schemes for the collisional breakup of ice particles. Simulation results reveal that the ice multiplication processes have a significant impact on the cloud microphysical properties and thermodynamic phase distribution within the cloud. At the cloud top, the fingerprint of ice multiplication is weaker. Collisional breakup is found to dominate ice multiplication, and the collisional breakup process rate is larger than rime splintering and droplet shattering process rates by 4 and 3 orders of magnitude, respectively. The ice enhancement factor (the ratio of ice mass or number in simulations with and without ice multiplication) has a strong vertical variation, with the maximum around -10°C and -25°C. Besides, the cascade effect on ice cloud number concentration was also investigated.
How to cite: Han, C., Hoose, C., and Dürlich, V.: Ice multiplication in simulated deep convective clouds with the ICON model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5327, https://doi.org/10.5194/egusphere-egu23-5327, 2023.
Warm conveyor belts (WCB) lead to formation of horizontally wide spread Cirrus clouds in the upper troposphere. However, the contribution of different ice formation processes and the resulting micro- and macrophysical properties of the Cirrus ,e.g., their radiative effects are still poorly understood. We want to especially address the research question of in-situ vs. liquid origin ice formation.
Common microphysics bulk schemes only consider a single ice class which includes sources from multiple formation mechanisms. We developed and implemented a two-moment microphysics scheme in the atmosphere model ICON that distinguishes between different ice modes of origin including homogeneous nucleation, deposition freezing, immersion freezing, homogeneous freezing of water droplets and secondary ice production from rime splintering, frozen droplet shattering and collisional break-up, respectively. Each ice mode is described by its own size distribution, prognostic moments and unique formation mechanism while still interacting with all other ice modes and microphysical classes like cloud droplets, rain and rimed cloud particles.
Using this novel microphysics scheme we can determine the contribution of the various ice formation mechanisms to the total ice content. For the first time this allows us to directly investigate the competition of in-situ and liquid origin Cirrus as well as homogeneous and heterogeneous ice nucleation with regards to environmental conditions and choice of microphysical parameterisations.
We performed an ensemble of simulations for selected WCB cases to cover a range of microphysical properties and compared the results of our liquid origin vs in-situ analysis with other Cirrus categorization algorithms.
How to cite: Lüttmer, T. and Spichtinger, P.: A novel approach to investigate Cirrus cloud formation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9818, https://doi.org/10.5194/egusphere-egu23-9818, 2023.
The global aviation fleet modifies cloudiness through contrail formation and their subsequent competition with natural cirrus for ambient water vapor, along with enhanced ice-nuclei concentrations from aircraft soot emissions. Contrails form in the upper troposphere at temperatures below 233 K and pressures below 300 hPa, when plume gases from jet engines, having appreciable water vapor content, saturate with respect to liquid water (Schmidt-Appleman Criterion, SAC). Realistic assessments of the aviation-induced modifications to global cloud cover demand improved representation of contrails and their interaction with background cloudiness in climate models. We have implemented a process-based parametrization of contrail cirrus, that applies to both young (≤ 5 h) and aged contrails, in the UK Met Office Unified Model, version 12.0. Contrail cirrus is introduced as a new prognostic cloud class, forming in the parametrized, fractional ice supersaturated area which then undergoes advection, depositional growth, sublimation and sedimentation. The proxy for the fractional supersaturated area is calculated using the same total water PDF as used for natural cirrus but with a different critical relative humidity, rcc - a value at which part of the model grid box is at least ice-saturated. The persistence of contrails being allowed in the ice supersaturated areas, the simulated coverage is not confined to flight corridors, but is advected to air traffic free zones as well. The simulated annual mean global coverage due to young contrails is 0.13%, with the main traffic areas of Europe and North America having the maximum coverage. Similar to natural cirrus, the contrail ice particles reflect the solar short-wave (SW) radiation and trap outgoing long-wave (LW) radiation, thereby modifying the radiative balance of the Earth’s atmosphere. Contrail cirrus is radiatively active in the model with forcing studies enabled via a ‘double radiation call’ approach, wherein parallel runs of the radiation scheme ‘with’ (prognostic) and ‘without’ (diagnostic) the contrail radiative effects isolates the contrail-induced perturbations. Contrails are seen to induce a short-wave cooling and long-wave warming and the net (SW+LW) direct top-of-atmosphere radiative forcing by young contrails amounts globally to 0.5 mWm-2, with the peak forcing seen along the main air traffic areas of North America, Europe and East Asia. The implementation of this process-based parametrization in the UM enables the simulation of the life cycle of persistent contrails, and can provide valuable insights to the aviation-induced modifications to the global cloud cover.
How to cite: Francis, T., Rap, A., Van Weverberg, K., Manners, J., Furtado, K., Zhang, W., Forster, P., and Morcrette, C.: Implementing a process-based contrail parametrization in the Unified Model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2964, https://doi.org/10.5194/egusphere-egu23-2964, 2023.
Warm conveyor belts (WCB) are regions of large-scale coherent airflow within extratropical cyclones that rapidly ascend from the boundary layer to the upper troposphere. During their ascent, WCBs transport water vapour and cloud condensate to the upper troposphere, and thereby significantly contribute to the moisture content of the extra-tropical upper troposphere-lower stratosphere (UTLS) as well as upper tropospheric cloudiness. UTLS moisture content and cloudiness are important for the radiative budget of the Earth and future changes thereof, but are often poorly represented in numerical models and reanalysis products. A detailed quantitative understanding of the processes governing water transport in WCBs provides vital clues to the origin of these biases and for evaluating predicted future changes in WCB moisture transport. Furthermore, recent studies have found that deep and embedded convection play an important role in WCBs. This points to the necessity of high-resolution simulations, that are well validated with observational data to provide a “benchmark” for coarser-resolution global (climate) models. Here we investigate the physical processes governing WCB moisture transport in simulations of a case-study from the WISE campaign with a particular focus on (i) the impact of grid spacing (including the use of convection parameterisations) on WCB moisture transport, (ii) the microphysical processes controlling moisture loss from the WCB, and (iii) the cloud microphysical properties of the cirrus clouds in the WCB outflow.
To this end we conducted two ICON simulations of an extratropical cyclone using (i) a global (~13km resolution), convection-parameterizing and (ii) a doubly nested (~13km, ~6km and ~3km resolution) convection permitting set up. In both set-ups online trajectories are calculated that capture convective ascent and allow for a Lagrangian analysis of WCB moisture transport and WCB cloud structure.
The Lagrangian metrics show large differences in ascent timescales and the efficiency with which water is transported from the boundary-layer to the UTLS. It is shown that this impacts the UTLS moisture content in the WCB outflow region. Local changes in UTLS moisture content induced by different representations of convection are shown to project onto larger-scale structures in the moisture and cloud fields over the 1-2 days after WCB ascent.
How to cite: Schwenk, C. and Miltenberger, A.: Physical processes controlling warm conveyor belt moisture transport to the UTLS and dependence on model resolution, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6987, https://doi.org/10.5194/egusphere-egu23-6987, 2023.
Posters on site: Tue, 25 Apr, 14:00–15:45 | Hall X5
Global climate models poorly represent mixed-phase clouds, which leads to uncertainties in cloud radiative forcing and precipitation. In the FORCeS ice experiment (FOR-ICE) we compare three global climate models (ECHAM-HAM, NorESM, EC-Earth) and show which processes are crucial for a realistic representation of cloud ice and supercooled water in each global climate model framework using the factorial method as a statistical approach. A specific focus of the experiments is on secondary ice production (SIP) - which apart from one mechanism (rime splintering) is typically not represented in models, even if observations of ice crystal concentrations of ice crystal number in warm mixed-phase clouds often exceed available ice nuclei by orders of magnitude. We evaluate the importance of three SIP mechanisms combined (rime splintering, ice-ice collisions, and droplet shattering) compared to all other processes that can modulate ice mass and number in mixed-phase clouds: ice nucleation, sedimentation, and transport of ice crystals, and the Wegener-Bergeron-Findeisen process. To describe SIP we adopt two approaches: an explicit microphysical representation of the processes, and a parameterization based on a random forest regression of high-resolution two-year simulations in the Arctic using the polar Weather Research and Forecast model (polar-WRF). Satellite observations are used to evaluate if including descriptions of SIP leads to a more realistic representation of mixed phase clouds.
How to cite: Ickes, L., Costa Surós, M., Eriksson, P., Frostenberg, H., Georgakaki, P., Gonçalves Ageitos, M., Hallborn, H., Lewinschal, A., May, E., Nenes, A., Neubauer, D., Pérez García-Pando, C., Proske, U., and Sotiropoulou, G.: How important are secondary ice processes – preliminary results from FOR-ICE, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10696, https://doi.org/10.5194/egusphere-egu23-10696, 2023.
Ice clouds constitute a challenge to satellite remote-sensing due to the variability of their microphysical properties. A central parameter to understand and represent ice clouds in modelling as well as in remote-sensing is the ice particle size distribution (PSD), whose shape largely varies depending on the environmental conditions in which the ice cloud has formed and evolved. This shape is typically assumed in satellite retrieval algorithm, for instance as a mono-modal gamma-modified distribution. Our representation of PSDs has greatly improved over the last decades, largely due to novel parameterisation methods as well as the increasing availability and accuracy of in-situ measurements that can serve as a solid basis to calibrate retrieval algorithms.
This study investigates the impact of the PSD shape assumptions on cirrus retrievals obtained from lidar-radar satellite observations (DARDAR-Nice), with a strong focus on the ice crystal number concentration. Recent in-situ measurements from the JULIA dataset were recently processed to propose new parameterisations of the PSD that offer a better representation of small ice concentrations. The added-value of considering the observed bi-modality when representing PSDs for remote sensing applications was also discussed. We here assess the consequences of including such new parameterisations in DARDAR-Nice. Comparisons between v1 and v2 (offering updated PSD assumptions) of this satellite product are also discussed.
Finally, preliminary results from a DARDAR-Nice simulator will be shown. This simulator allows to perform synthetic lidar-radar observations and retrievals on high-resolution cloud model outputs. Comparisons between the model “truth” and synthetic retrievals will be investigated and discussed in the context of underlying PSD assumptions.
How to cite: Sourdeval, O., Bartolome Garcia, I., Penide, G., and Krämer, M.: Sensitivity of Satellite Lidar-Radar Cirrus Retrievals to PSD Assumptions: DARDAR-Nice v2 and Simulator, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15765, https://doi.org/10.5194/egusphere-egu23-15765, 2023.
Atmospheric constituents, such as aerosols and clouds, greatly affect the
radiative properties of the atmosphere. Clouds play a substantial role in this
radiative balance. To better understand the contribution of cirrus clouds im-
proved modelling and in-situ observations are needed.
For further improving current climate-modelling parameters, accurate pa-
rameterization of these clouds are required. From in-situ measurements, the
size distribution of cirrus ice particles, their concentration and shape param-
eters can be determined. This can be achieved with the iBalloon-borne Ice
Cloud particle Imager (B-ICI). Campaigns done with the B-ICI and resulting
parameetrizations have contributed to more accurate characterization of cirrus
clouds.
The B-ICI is collecting and imaging ice particles with a pixel resolution
of 1,65 µm/pixel. With detailed image analysis at this accuracy particles >
20µm can be distinguished, dimensions and concentration can be derived, and
particles can be sorted according to their shape. An improved version of B-ICI
is currently being developed. This new version of the instrument is primarily
improving image quality to enable easier and more automated image processing.
Secondarily, changes in the design will reduce the weight of the instrument
and simplify the method for sampling of ice particles. A more light-weight
instrument will allow adding other sensors. In particular, an optical particle
counter to measure aerosol and small ice particles will be added to the B-ICI.
This addition of an optical particle counter will result in more accurate size
distributions in addition of providing complementary aerosol measurements. In
this paper, we will highlight these changes and improvements in the B-ICI set-
up.
How to cite: Stenszky, J. and Kuhn, T.: Improving the Balloon-borne Ice Cloud Particle Imager (B-ICI), EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-829, https://doi.org/10.5194/egusphere-egu23-829, 2023.
Secondary ice processes (SIPs) can produce ice crystals with a number concentration much higher than that of ice nucleating particles (INPs) in mixed-phase clouds, and therefore influence cloud glaciation and precipitation. But the role of SIPs in midlatitude continental mesoscale convective systems (MCSs) such as squall lines is still unknown. This study investigates the relative importance of rime splintering, freezing drop shattering, and collision breakup in the mature stage of a squall line case in North China on 18 August 2020 using the WRF model. The simulations show that collision breakup has the most pronounced effect on ice production, and rime splintering plays a secondary role. It is because ice multiplication from SIPs can feedback to collision breakup and rime splintering in different ways. Collision breakup has a positive feedback because the numerous snow and graupel from SIPs in turn promote a higher collision breakup rate, while rime splintering is limited by itself and also limited by collision breakup because the weaker riming due to the two SIPs leads to a lower rime splintering rate. Freezing drop shattering has a negligible effect on ice production because there are few large droplets in the mature stage. Collision breakup can also redistribute surface precipitation in the squall line, which decreases in the convective region and increases in the stratiform region. The influence of aerosols as CCN and INPs on SIPs is further studied. Preliminary simulation results show that the effects of aerosol concentration on the rate of SIPs and anvil ice concentration are nonlinear. The mechanism remains to be analyzed.
How to cite: Gao, J. and Xue, H.: Modeling Secondary Ice Processes on a midlatitude squall line, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4195, https://doi.org/10.5194/egusphere-egu23-4195, 2023.
The representation of Arctic clouds in numerical weather prediction models is challenging, especially for mixed-phase clouds with both a liquid and ice phase present. We compare measurements conducted during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign, which took place in May/June 2017 northwest of Svalbard, Norway, with the operational ‘Atmospheric Model high resolution’ configuration (HRES) of the Integrated Forecasting System (IFS), operated by the European Centre for Medium-Range Weather Forecasts (ECMWF). Instead of using cloud retrieval products from airborne remote sensing, the comparison is performed in the observational space of spectral solar irradiances reflected by the clouds. To allow such an analysis along the flight track at flight level, the operational ecRad radiation scheme of the IFS is used in offline mode. Besides the HRES model output, vertical profiles of concentrations of trace and greenhouse gases provided by the ECMWF Atmospheric Composition Reanalysis 4 serve as the input for ecRad. The ability of the IFS to realistically represent the airborne radiation measurements collected during ACLOUD is evaluated for flight sections above sea ice and open ocean. Inconsistencies between the upward irradiance observed during ACLOUD and the simulations by ecRad are found and may originate from uncertainties introduced by the cloud fraction, the cloud phase, the sea ice albedo, and the ice optics parameterization. Our analysis aims to separate the influence of the different macro- and microphysical parameters on the upward irradiance. To disentangle the impact of these parameters, the spectral irradiance is analyzed where e.g. the impact of liquid and ice phase can be separated. Different case studies give insight into a sub-grid cloud cover variability that is not seen by the IFS above open ocean and an overestimation of the measurements by ecRad above sea ice that can be explained by the lack of cloud brightness. EcRad is additionally run with improved ice optics parameterizations. The choice of the applied ice optics becomes more important with an increasing ice water path of the clouds and is investigated in detail within the near-infrared bands of ecRad.
How to cite: Müller, H., Röttenbacher, J., Schäfer, M., Ehrlich, A., and Wendisch, M.: Representation of Arctic mixed-phase clouds in ECMWF forecasts during ACLOUD, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6077, https://doi.org/10.5194/egusphere-egu23-6077, 2023.
Ice crystal number concentrations were often found to be orders of magnitude higher than the number concentration of ice nucleating particles; a finding that indicated the presence of secondary ice production (SIP). Although 6 mechanisms of SIP have been both discovered and theorized, it is still not fully understood and the recent studies have been inconclusive in identifying the dominant process in real conditions. This lack of constraint of ice multiplication adds to the uncertainty of cloud simulations in climate models. Studying SIP is challenging due to the various interfering factors involved.
In this study, we attempt to further our knowledge in understanding the SIP mechanisms using two different but complementary approaches. The first consists of using remote sensing tools such as Himawari-8 and MODIS retrievals in addition to the SOCRATES in-situ data to identify the presence of SIP and categorize the possible mechanism involved.
The second approach utilizes numerical simulations to further understand these mechanisms that are potentially responsible for SIP, but through the study of the dynamics of the different particles (ice crystals, supercooled droplets, graupel...) involved in these processes. In this approach we focus on the characteristics of the particles, such as their diameter and concentration, as well as the presence of turbulence, that are crucial in describing their movement and the feasibility of the mechanisms under study.
How to cite: Le Roy De Bonneville, F., Aboel Fetouh, Y., Cermak, J., Hoose, C., Järvinen, E., Leisner, T., and Uhlmann, M.: Studying secondary ice production mechanisms: from a remote sensing and hydrometeors dynamics perspective, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14247, https://doi.org/10.5194/egusphere-egu23-14247, 2023.
Ice clouds are challenging because of the high complexity and diversity of their composition (microphysics) as well as formation and growth processes. As a result, there has been little constraint from observations until recently, resulting in significant limitations in our understanding and representation of ice clouds. A major problem with satellite measurements is the lack of information on the environmental context, which is necessary to identify and understand the formation mechanism and evolution of clouds; these renditions indeed only represent a snapshot of the state of a cloud and its microphysical properties at a given time. This work tackles this issue by providing additional metrics on ice cloud history and origin along with operational satellite products.
Here, we present a novel framework that combines geostationary satellite observations with Lagrangian transport and ice microphysics models, in order to obtain information on the history and origin of air parcels that contributed to their formation. The trajectory of air parcels encountered along the DARDAR-Nice track has been traced using the air mass transport models CLAMS (Chemical LAgrangian Model of the Stratosphere). CLaMS - Ice model is jointly used to simulate cirrus clouds along trajectories derived by CLaMS. This approach provides information on the cloud regime as well as the ice formation (in-situ vs liquid origin) pathway. For tropical cirrus of convective origin, a Time Since Convection dataset from geostationary observations can also be incorporated into this approach. Preliminary results of this approach obtained on case studies representative of multiple cloud types will be shown here.
How to cite: Saiprakash, A., Konjari, P., Horner, G., Rolf, C., Krämer, M., and Sourdeval, O.: Investigating ice cloud formation mechanisms from satellite observations and Lagrangian transport and microphysics models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14329, https://doi.org/10.5194/egusphere-egu23-14329, 2023.
Clouds are a fundamental aspect of the Earth’s atmosphere. One of the major challenges in cloud-resolving models (CRM) is the formation and generation of new cloud ice particles from pre-existed ice and liquid. Based on the basic broad cloud types, it is helpful to distinguish between their fundamental microphysical properties. The four basic cloud types are defined as: (1) warm-based convective and stratiform clouds; and (2) cold-based convective and stratiform clouds. Recent studies of ice initiation in clouds have shown that most ice particles in the mixed-phase region of clouds are from secondary ice production (SIP) mechanisms but have generally concentrated on only one specific cloud system.
In this study, Aerosol-Cloud model (AC) is used. AC includes the four mechanisms of secondary ice production as follows: ice-ice collisional breakup, raindrop freezing fragmentation, Hallett-Mossop (HM) process and sublimational breakup. The intent is to generalize the contribution of each SIP mechanism among basic cloud types. The numerical simulations are performed using our AC for each cloud type and validated against in-situ cloud observations. The observational data is collected during four different cloud observational campaigns, each representing a contrasting cloud type than others.
Here, we study the contributions from each process of SIP (HM process, ice-ice collisional breakup, raindrop-freezing fragmentation and sublimational breakup) by performing control simulations of each basic cloud type. For the warm cloud convective clouds, the HM process prevails near freezing level and contributes significantly from 0 to -15oC. In cold-based convective clouds, the ice-ice collisional breakup is the most dominating SIP mechanism in each cloud type. In warm-based stratiform clouds, the HM process dominates the contribution of ice in the -5 to -15oC temperature range for updrafts up to 8 m/s. In the slightly warm-based convective clouds, the breakup due to ice-ice collision is the most dominating mechanism for the convective updrafts between -5oC and cloud top temperatures.
How to cite: Deshmukh, A., Phillips, V., Waman, D., Patade, S., Bansemer, A., and Gupta, A.: Organization of SIP mechanisms among basic cloud types, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15890, https://doi.org/10.5194/egusphere-egu23-15890, 2023.
The Upper Troposphere-Lower Stratosphere (UTLS) is a transition region for coupled dynamical, chemical and microphysical processes. These coupled processes play an essential role in climate change. Water vapor, ozone and aerosols in the UTLS region have important impacts on the Earth’s radiation budget. Systematic biases in UTLS moisture are known to exist in global climate models. Understanding the sources of UTLS moisture and quantifying the transport processes that control water vapor and clouds in the UTLS can provide important insights into the model uncertainties and improve model simulations. In the extratropics ascending airstreams in extratropical cyclones, particularly the warm conveyor belt (WCB), and deep convection are thought to be the most important sources of UTLS moisture. Here, we utilize ERA5 reanalysis data and IAGOS aircraft measurements to quantify the contribution of WCBs to UTLS moisture for the decade 2010 to 2019. WCB outflow regions are defined using Lagrangian trajectories. The moisture anomaly in the WCB outflow compared to average UTLS moisture content is quantified as well as its evolution over the 2 days after WCB ascent. ERA5 suggests significant positive moisture anomalies in the WCB outflow that persists over several days. Finally, ERA5 UTLS moisture content is compared to IAGOS humidity measurements with a particular focus on WCB outflow regions. In summary, we present a comprehensive climatological picture of the role of WCB moisture transport for the UTLS composition.
How to cite: Guo, Z., Schwenk, C., Boettcher, M., Brast, N., Reutter, P., and Miltenberger, A.: Climatological analysis of warm conveyor belt contributions to UTLS moisture content, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6114, https://doi.org/10.5194/egusphere-egu23-6114, 2023.
The representation of orographic clouds in numerical weather prediction models remains a great challenge, as a consequence of our incomplete understanding of the microphysical processes acting on them and the complex interactions between the large-scale and orographic flow dynamics. Mixed-phase conditions are frequently occurring in orographic clouds, highlighting the importance of correctly simulating the microphysical evolution of ice- and liquid-phase hydrometeors. In this study we employ the mesoscale Weather Research and Forecasting (WRF) model to investigate the drivers of intense snowfall events observed during the Cloud-AerosoL InteractionS in the Helmos background TropOsphere (CALISHTO) campaign, that took place from Fall 2021 to Spring 2022 at Mount Helmos in Peloponnese, Greece. Vertical profiles of reflectivity, Doppler velocity, as well as full Doppler spectra measured by a vertically pointing W-band (94 GHz) Doppler cloud radar, in synergy with Doppler and aerosol depolarization lidar data, help gain insight into the snowfall microphysics involved and set the basis for evaluating the performance of the WRF model. A radar simulator coupled with WRF enables the direct comparison between the mesoscale simulations and remote sensing products, and allows us to find the optimal model set-up that minimizes deviations from the observations. Comparing the modeled ice crystal number concentrations (ICNCs) with the Ice Nucleating Particles (INPs) measured in-situ at the Helmos High Altitude Monitoring Station (2314 m, 42°N 05' 30'', 34°E 14' 25'') by the Portable Ice Nucleation Experiment (PINE) instrument, we seek to quantify the ice enhancement factors due to secondary ice production (SIP) or seeding ice particles and their potential role in enhancing orographic precipitation. The synergy between high-resolution modeling and radar observations gives us the opportunity to infer SIP signatures from remote sensing observations, which is an important outcome given the abundance of the latter.
How to cite: Georgakaki, P., Billault-Roux, A.-C., Perrin, E., Foskinis, R., Sotiropoulou, G., Vogel, F., Gini, M., Eleftheriadis, K., Moehler, O., Takahama, S., Berne, A., and Nenes, A.: Unraveling secondary ice production in winter orographic clouds through a synergy of in-situ observations, remote sensing and modeling, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14023, https://doi.org/10.5194/egusphere-egu23-14023, 2023.
Measurements were made in 2 sets of cold air outbreaks using the UK FAAM BAE 146 research aircraft. The first set were performed in March 2022 over the Eastern Atlantic the second set were perform in October to early November 2022 in the Western Atlantic over the Labrador Sea based in Goose Bay, Eastern Canada. In each set of experiments the focus was to study the evolution of the cloud microphysics as influenced by Cloud condensation nuclei, ice nuclei and secondary ice processes in the stratocumulus clouds being advected southwards over progressively warmer sea until cloud break-up occurred into convective clouds. The aims were to improve the treatment of these cloud types in Global climate models and weather forecast models. These projects formed part of m-Phase funded by NERC as part of its Cloud Sense programme and ACAO a Met office program to study these clouds.A range of aerosol and cloud microphysical equipment was used in the 2 projects which will be discussed in the presentation.Analysis of the data set including a new novel Holographic instrument is still underway at the time of writing; however, some preliminary results indicate that:
- Generally the ice crystal number concentration exceeded the ice nucleus concentrations measured at the same temperature
- Some regions consisted entirely of super cooled water
- A range of secondary ice particle production mechanisms were observed including ice splinter production during riming and droplet shattering on freezing after capture by ice crystals
- Generally if the convective region was reached by the aircraft then secondary ice production was greater than in the stratocumulus region
- Precipitation was mostly in the ice phase
How to cite: Choularton, T. and the M-phase ACAO: Measurementsof microphyscs in cold air Outbreks, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7474, https://doi.org/10.5194/egusphere-egu23-7474, 2023.
Observations of cloud related processes in the Arctic are needed to evaluate the representation of clouds in weather and climate models and to improve our understanding of processes of Arctic amplification and Arcitc-midlatitude linkages. One remaining uncertainty of the Arctic climate system are cirrus clouds and their influence on the radiative budget. Arctic cirrus is known to warm the climate system on annual average, especially when present over the sea ice covered central Arctic.
The HALO-(AC)³ airborne campaign in spring 2022 investigated changes within air masses on their way in and out of the central Arctic with the High Altitude LOng Range research aircraft (HALO), which was equipped with a suite of remote sensing instrumentation. Two flights were used to explicitly investigate the cloud radiative effect of single layer isolated cirrus between 81 and 90 degrees North.
Flight legs above and below the cirrus with measurements of spectral solar irradiance from the Spectral Modular Airborne Radiation measuremenT system (SMART) make a direct estimation of the cloud radiative effect possible. The cirrus was sufficiently thick to reduce the transmission of solar radiation by around 25%. However, significant inhomogeneities in the cirrus were observed.
We present a case study of the radiative effect of Arctic cirrus and compare airborne irradiance measurements to simulations from an offline run of the ecRad radiation scheme which is operationally used in the ECMWF's Integrated Forecasting System.
How to cite: Röttenbacher, J., Müller, H., Ehrlich, A., and Wendisch, M.: Quantification of the Radiative Effect of Arctic Cirrus by Airborne Radiation Measurements - A Case Study, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7012, https://doi.org/10.5194/egusphere-egu23-7012, 2023.
The role of gravity waves on microphysics of tropical cirrus clouds and air parcel dehydration was studied using the combination of Lagrangian observations of temperature fluctuations and a 1.5 dimension model. High frequency measurements during isopycnal balloon flights were used to resolve the gravity wave signals with periods ranging from 15min to a few days. The detailed microphysical simulations with homogeneous freezing, sedimentation and a crude horizontal mixing represent the slow ascent of air parcels in the Tropical Tropopause Layer. A reference simulation describes the slow ascent of air parcels in the tropical tropopause layer, with nucleation occurring only below the cold point tropopause with a small ice crystals density. The inclusion of the gravity waves modifies drastically the low ice concentration vertical profile and weak dehydration found during the ascent alone: numerous events of nucleation occur below and above the cold point tropopause, efficiently restoring the relative humidity over ice to equilibrium with respect to the background temperature, as well as increase the cloud fraction in the vicinity of the cold-point tropopause. The increased ice crystal number and size distribution agree better with observations.
How to cite: Corcos, M., Hertzog, A., Plougonven, R., and Podglajen, A.: An idealized model to assess the impact of gravity waves on ice crystal populations in the Tropical Tropopause Layer, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2309, https://doi.org/10.5194/egusphere-egu23-2309, 2023.
