The observatory at Skalnaté Pleso, Slovakia, serves as a facility for both astronomical and meteorological research in the High Tatra Mountains. It is located at an altitude of 1778 meters a.s.l. on the south-eastern slopes of the Lomnický Peak near the Tatranská Lomnica municipality. The observatory was established in 1943 by Dr. Antonín Bečvář, a Czech astronomer and meteorologist. His well-known works, the famous sky charts (i.e. Atlas Coeli) and photographs of mountain clouds were based on observations made at the Skalnaté Pleso Observatory. Nowadays, astronomical measurements are made under the supervision of the Astronomical Institute of the Slovak Academy of Sciences, which also operates another observatory located at the Lomnický Peak (2634 m a.s.l.) and two telescopes at the Stará Lesná Observatory (810 m a.s.l.). These observatories are used to study interplanetary matter, solar, and stellar physics. Apart from astronomical research, the Skalnaté Pleso Observatory provides standard climatological measurements including measurements of air temperature, air pressure, relative humidity, snow cover, precipitation, sunshine duration, wind speed, and wind direction since as early as 1943. With only minor modifications, the methodology of meteorological observations remained the same up until today. In 1962, the meteorological observatory was incorporated into the Slovak Academy of Sciences, currently the Earth Science Institute, and the mission of the station was extended to cover research mostly in the field of energy and radiation balance. Later, measurements of ozone concentrations were initiated, and an automatic weather station was installed. This enabled the extension of ozone research to its phytotoxicity on vegetation and beyond. The advance in automatic weather stations has introduced important questions regarding the comparability of automatic measurements with standard (conventional) measurements conducted by observers.

How to cite: Buchholcerová, A., Onderka, M., and Lukasová, V.: The past, present, and future of the observatory at Skalnaté Pleso, High Tatras, Slovakia, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-462, https://doi.org/10.5194/ems2023-462, 2023.

How to cite: Hervo, M., Haefele, A., Bättig, P., Leuenberger, D., Merker, C., Regenass, D., Kaufmann, P., and Arpagaus, M.: An integrated meteorological forecasting system for emergency response, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-573, https://doi.org/10.5194/ems2023-573, 2023.

We present an investigation of the structure of the aerosol layer at the Villum Research Station located at Station Nord in the high Arctic. Knowledge of the aerosol layering is of interest for the interpretation of measurements of atmospheric chemistry and particles that control air pollution in the pristine atmosphere and for climate change (Arctic amplification). Based on one year of remote sensing measurements by a ceilometer and a wind lidar, we discovered that the structure of the atmosphere was very different from what is usually found at mid-latitudes. Combining the ceilometer and wind lidar observations indicated that the aerosol layer has depths of about 100 m and 230 m and few cases of depth between 100 and 230 m. Studies of profiles with no aerosol-layer depth, based on high frequency ceilometer observations, reveal cases of entraining air. We found that the annual wind roses indicate generally westerly wind veering by more than 30 degrees between 40 and 200 m and a wind speed slowly increasing with height of about 5 m/s. It was found that the individual wind speed profiles between 40 and 200 m can roughly be categorized into 4 groups: 1. The wind speed increases from the ground up to 100m and thereafter decreasing (likely drainage); 2. The wind profile decreases from the ground up to a minimum at about 100 m; above this minimum the wind speed increases (no explanation for this type of wind profile is offered); 3. Wind speed increases with altitude; 4. Wind speed decreases from the ground throughout the whole layer. The two-layer structure of the aerosols and the different categories of wind profiles complicates the interpretation of surface observations. We discuss the implication in terms of local versus remote sources of aerosols and the uncertainty in backward trajectory modelling. These data can be used further for meteorological and aerosol model validation in the lower atmosphere of the High Arctic.

Funding information: Danish Environmental Agency ‘Monitoring of short-lived climate components in Arctic’; European Cooperation in Science and Technology, Grant/Award Number: COST Action CA18235 PROBE; National Science Fund of Bulgaria, Grant/Award Number: KП-06-Н34/1; Nationalt Udvalg for Forskningsinfrastruktur (NUFI) 

How to cite: Gryning, S.-E., Batchvarova, E., Floors, R., Muenkel, C., Sørensen, L. L., and Skov, H.: Aerosol-layer structure and wind profile in the high Arctic, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-561, https://doi.org/10.5194/ems2023-561, 2023.

According to a survey by the World Meteorological Organization (WMO) there is a serious lack of data from measurements describing the vertical characteristics of the atmosphere. This, besides the insufficient determination of the current state, also affects the accuracy of meteorological forecasts. WMO sees the use of Uncrewed Aircraft Systems (UAS) for atmospheric measurement as a possible solution to this problem. Therefore, WMO coordinates a global campaign in 2024 to demonstrate the capabilities of UAS measurements as a possible operational data source. From Hungary, MouldTech Systems (MTS) is the only registered participant so far, and they started the development of an UAS-based measurement network for routine atmospheric vertical profile measurements. The measuring UAS was designed and manufactured at MTS considering the operational weather limits of the flights to approach the level of applicability as radiosondes. The flyability of UAS was validated using ECMWF ERA5 reanalysis fields. The average values of applicability are between 90-95% at the planned measurement sites. MTS as a drone operator organization has already obtained operational authorization from the national competent authority for three different locations in Hungary to perform the profiling operation. During this operation, the drone can climb up to 2500 m AMSL to cover the height of the planetary boundary layer regardless of seasons. In accordance with the WMO's expectations the redundantly installed sensors measure the temperature, the humidity, and the pressure. Besides these variables, the wind vectors are calculated from the telemetry data provided by UAS. All the meteorological information is collected in our data server in real-time via LoRa communication. On an experimental basis, the measured data are assimilated into our numerical weather prediction model to gather as much experience as possible to estimate the effective range of the data assimilation in our NWP domain and determine the ideal spatial density of the measurement sites. In summary, in our presentation, besides the achieved outcomes of the development and the bridged obstacles, we would like to introduce the UAS itself, the complete functionality of the measurement network, and the related future challenges of normal operation.

How to cite: Bottyán, Z., Gyöngyösi, A. Z., Kardos, P., Tuba, Z., and Vranics, F. D.: Development of UAS-based measurement network for routine atmospheric vertical profiling, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-298, https://doi.org/10.5194/ems2023-298, 2023.

The LES based modelling system PALM has been widely extended during recent years. A lot of the development focused on the processes needed for simulation of complex urban environments. Besides individual validations of the newly developed processes, an evaluation of the complete modelling system in a real urban environment is necessary to ensure the reliability of modelling results. Such comprehensive validation requires the construction of additional monitoring networks within the areas of interest to obtain sufficient data support.

Our earlier campaigns, e.g. Resler et.al. (2017, 2020), focused mainly on validation of the energy exchange related processes in urban area. As part of the currently running international TURBAN project, a measurement campaign was implemented in the center of Prague, Czech Republic. It focuses mainly on evaluation of the street level meteorological and air quality dynamical processes by utilisation of a specially built sensor network placed in heavily polluted street canyons (traffic-related pollution). Twenty air quality sensors were complemented by a doppler lidar and microwave radiometer profile observations, and by observations from permanent meteorological and air quality monitoring stations operated by the Czech Hydrometeorological Institute (CHMI). These data were compared with PALM simulations performed for selected episodes of the year. The PALM model was configured in two nested domains with resolution of 10 m / 2 m and the extent of 8×8 km / 1.2×1.6 km.

A significant challenge to the measurement campaign was the low accuracy and reliability of air quality sensor observations. The differences in the values of individual sensors as well as their deviations from the reference observations reached tens of percent. Using sufficiently long co-measurement with the reference monitoring station and advanced statistical methods, sufficiently accurate and reliable data suitable for model evaluation were obtained. To ensure long-term quality control of the observations, two selected sensors were co-located with a continuous reference CHMI station within the simulation domain. Similarly, setting up a profile measurement (especially with Doppler LIDAR) to obtain the maximum possible information in a given space and processing a large amount of data was a challenge. The presentation shows the details of the observations and their processing as well as the preliminary results of the model evaluation.

How to cite: Bauerová, P., Keder, J., Šindelářová, A., Patiño, W., Vlček, O., Krč, P., Resler, J., Geletič, J., Řezníček, H., Bureš, M., Eben, K., Belda, M., Radović, J., Fuka, V., Jareš, R., Sühring, M., and Ezau, I.: Measurement campaign focused on meteorology and air quality to support the validation of the PALM LES model in Prague, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-536, https://doi.org/10.5194/ems2023-536, 2023.

World Optical Depth Research and Calibration Center (WORCC) is participating in the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS), Switzerland program as part of the  ACTRIS Calibration of Aerosol Remote Sensing (CARS). In the ACTRIS-CARS program, WORCC maintains three precision filter radiometers (PFRs) at Izanã (IZO) in Spain, Observatoire de Haute Provence (OHP) in France and University of Valladolid (VLD) in Spain which are the main calibration facilities of ACTRIS sun photometers. The aim of this collaboration is to link the AOD product from ACTRIS-CH with the AOD scale recognized by the WMO and maintained by WORCC.

In this analysis, the AOD measurement comparisons were performed between ACTRIS-CARS PFR and Aerosol Robotic Network (AERONET)-Europe CIMEL sun-photometers at IZO, OHP and VLD for 2021 and 2022. The comparisons are performed in common wavelengths and also PFR AOD is extrapolated to the non-matching CIMEL wavelengths using Ångström law. The annual comparison results of PFR and CIMEL AOD at IZO showed that more than 99% of AOD differences were within the WMO uncertainty limits for all wavelengths above 340 nm. In case of OHP, more than 99% percentage of AOD differences were within the WMO uncertainty limits for all wavelengths longer than 440 nm while it was above 80% for all wavelengths except 340 nm. At VLD, the percentage of AOD differences within the WMO uncertainty limits were mostly above 99% for all wavelengths above 440 nm and above 90% for all wavelengths except 340 nm. In additions, instruments were inter-compared during the fifth filter radiometer campaign (FRC-V) held in 2021 and differences with the Davos reference triad of PFRs were mostly within the WMO limits.

Acknowledgment 

The work has been supported by the  Aerosol, Clouds and Trace Gases Research Infrastructure – Swiss contribution funded by the State Secretariat for Education, Research, and Innovation, Switzerland.

How to cite: Masoom, A., Kouremeti, N., Barreto, A., Toledano, C., Podvin, T., Blarel, L., Dubois, G., Gröbner, J., and Kazadzis, S.: Traceability of Aerosol Optical Depth measurements and links with the Aerosols, Clouds and Trace Gases Research Infrastructure (ACTRIS) / Calibration of Aerosol Remote Sensing (CARS), EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-373, https://doi.org/10.5194/ems2023-373, 2023.

Continuous long-term in-situ measurements of reactive trace gases in observational and environmental chamber platforms is essential to identify their impact on future air quality under climate change and the switch to renewable energy. Despite new and more advanced technologies for online and/or offline monitoring using pre-concentration and thermal desorption (TD), followed by gas chromatography (GC) coupled to mass spectrometry (MS) and/or flame ionization detection (FID), the complexity of such measurements is still challenging.

Within the framework of the ACTRIS Centre for Reactive Trace Gases in Situ Measurements CiGAS, this work presents the characterization and orthogonal comparison of two modern systems for online and offline sampling, respectively, coupled to GC dual-columns (Deans Switch heart cut approach) and FID/MS detection. We evaluate the advantages and limitations of these systems regarding the versatility of the sample inlets during collection (e.g., direct line, canisters, and multi-bed TD tubes) as well as automated calibration strategies (e.g., variable sample volume through MFC and loop mode), providing differences in compound coverage, signal responses and sorbent background. We evaluate their performance in terms of sensitivity, reproducibility, linearity, and relative recovery by performing, (1) laboratory calibrations using high purity certified mixtures of non-methane hydrocarbons and monoterpenes and, (2) ambient measurements using the characterized and calibrated analytical methods with particular emphasis on urban emissions from cooking, cleaning, and traffic. In addition, we compare results from the TD-GC-FID/MS to a high time resolution chemical ionization mass spectrometer, called VOCUS, and present the resulting volatile profiles, their variability, and interferences among the different measurements methods.

How to cite: Marcillo Lara, A. C., Grasse, A., Wedel, S., Roska, M., Alwe, H. D., Kiendler-Scharr, A., Gkatzelis, G. I., and Tillmann, R.: Characterization and applicability of online and offline monitoring systems for reactive trace gases using TD-GC-FID/MS analysis, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-509, https://doi.org/10.5194/ems2023-509, 2023.

Cosmic-ray albedo neutron sensing (CRNS) is a modern technology that can be used to continuously measure the average water content in the environment (i.e., in soil, snow, or vegetation). The sensor footprint encompasses an area of 10-15 hectares and extends to 20-50 decimeters deep into the soil. Thereby it can capture relevant root-zone soil moisture for drought analysis while being insensitive to small-scale heterogeneity. The method can be an alternative to conventional in-situ sensors or to expensive sampling of soil or snow. It also has the potential to bridge the scale gap between point-scale measurements and remote-sensing data in both, the horizontal and the vertical domain.

Currently, more than 200 sensors are operated in the growing networks of national and continental observatories across the globe. CRNS stations are continuously monitoring the local water dynamics at various sites worldwide. They require almost no maintenance over the years due to a solar module, battery and telemetry. Since the method works non-invasively, the soil is left undisturbed. The passive sensing technique measures natural cosmogenic background radiation which interacts with hydrogen in the ground independent of temperature, frost, or wind effects. CRNS can also be used on mobile platforms for on-demand soil moisture mapping at the field-, regional, or even national scales. The sensors are rapidly operational on any ground- or airborne vehicle.

In this presentation we will demonstrate how stationary and mobile CRNS can help to quantify the temporal as well as spatial distribution of water in soil or snow for various sites in Germany, Europe, and beyond. We will also discuss applications of long-term monitoring networks in combination with hydrological modeling and remote sensing. The data can be particularly useful to study hydrological extreme events, droughts, heatwaves, floods, snow melt/accumulation, and it can be applied as a lower boundary condition in atmospheric models, in hydrological models, in agricultural irrigation management, or for drought impact analysis.

How to cite: Schrön, M., Zacharias, S., Beyrich, F., Böttcher, F., Schattan, P., Altdorff, D., Fatima, E., Boeing, F., Kumar, R., Samaniego, L., Attinger, S., and Dietrich, P.: Monitoring soil moisture & snow water equivalent with cosmic-ray neutrons across scales, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-529, https://doi.org/10.5194/ems2023-529, 2023.

The latest Swiss hydrological scenarios predict more frequent and longer-lasting droughts. The Federal Council has just commissioned the establishment of a national drought monitoring and forecasting system based on an integrative approach using in situ, satellite and modeled data. A key element is the installation of a national near-real time in situ soil moisture network that will transfer existing research networks into a long-term secured operational service with homogenized quality control. Where necessary, new additional sites shall enhance spatial representativity.

In addition to drought monitoring, the collected data should also be suitable for use in numerous other applications. The network shall consist of about 30 grassland and forest stations distributed throughout Switzerland. The grassland stations will be exclusively collocated with existing meteorological stations. A good link to the existing Swiss irrigation network with a large number of soil moisture measurements in cultivated fields will be ensured. 

In order to capture the soil water characteristics curve as well as possible, continuous measurements of both volumetric soil moisture and water potential are planned. In addition, auxiliary soil parameters essential for process understanding and modeling will be collected throughout the soil profiles at each site.

Currently, technical implementation issues are being addressed and the soils from a pre-defined set of potential sites are being pre-sampled by the Swiss Competence Center on Soils in order to assess their quality as national sites. The installation phase is scheduled to begin in spring 2024 at the latest and be completed by the end of 2025.

In this contribution the project and its current status will be detailed.

How to cite: Bircher-Adrot, S., Roulet, Y.-A., Aellen, J.-M., Grandjean, J., Widmer, A., Félix, C., and Humphrey, V.: A national in situ soil moisture measurement network for Switzerland, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-408, https://doi.org/10.5194/ems2023-408, 2023.

Accurate observations of surface soil heat flux are an integral part of better understanding land surface-boundary layer interactions. Surface soil heat flux is typically derived from a combination of soil temperature and soil heat flux sensors at various levels below the surface. Over time, the action of soil fauna, weathering (rain and frost), and gravity, shifts the plant material, soil, and ultimately, the sensors. If not accounted for, this displacement causes uncertainty in surface soil heat flux estimations, becoming especially relevant for long-term observations. Yet these same long-term observations can also be used to evaluate the reliability and stability of soil thermal measurements. Aptly, a variety of soil observations are available at a mid-latitude grassland site since 1986 as a part of the Cabauw in-situ program. We analyse the timeseries from 2003 – 2019, investigating the history, vertical movements, and positional problems of the soil heat flux sensor system as well as the complex application of these measurements for Surface Energy Balance (SEB). We examine the sensor movement in the soil by comparing the phase of the topsoil temperature and the soil heat flux at 0.05-m depth to the phases of the shortwave downward radiation and 2-m air temperature. Naturally, we observe gradual sinking and displacement of the soil sensors. In fact, some components were found approximately 0.05 m lower, 15 years after burial. In 2015, a new soil thermal system was reconstructed with sensors positioned as precisely as possible, and after one year, the grass conditions were comparable to the surrounding terrain. Therefore, we assume that the top sensors are still in the correct vertical position during the one year of observations taken after this point and compare the soil heat flux to the old sensor system. We observe large discrepancies in the contribution of the soil heat flux to the SEB for the new and old system, highlighting the importance of accurate soil observations.

How to cite: Strickland, J. and Bosveld, F.: Long-term stability and vertical displacement of soil sensors at Cabauw site, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-598, https://doi.org/10.5194/ems2023-598, 2023.

Declining water availability is among key global concerns in the modern society manifesting uniquely at different scales, from the farm field to the global food distribution, and requires innovative composite solutions in terms of policy, education, science, and technology. Solutions to water use in agriculture require resource management based upon socioeconomic and scientific understanding.

These important goals are achieved through crucial regulatory, societal, and technical means. Among the latter, monitoring of water flows at multiple scales, from the field to the state and beyond, can help achieve water use reduction, optimization and prediction. Even small water savings, when achieved at scale, can bring about massive benefits. To properly track and document single digit percent improvements, measurement accuracy is especially important, and cannot ordinarily be achieved with indirect evapotranspiration (ET) estimations such as potential, reference or equilibrium ET models based on weather data. A fundamental component of a dense, coordinated grid for effective water monitoring is therefore the accurate, real-time, high spatio-temporal resolution measurement of direct water use and transport.

In this work we present the main features and specifications of the very latest technology specifically developed for affordable yet accurate, direct, unattended, and automated field-scale ET measurements. We discuss laboratory performance evaluations as well as field testing against reference methods, with a focus on the scientific and technological trade-offs underlying the innovative design. Representing the synthesis of three decades of expertise in the design and development of research-grade systems for the quantification of in-situ gas and energy flux, this new technology is specifically intended to enable and encourage the creation of new, denser networks of unmanned ET measurements.

How to cite: Fratini, G., Miller, B., McCoy, J., Walbridge, R., Frodyma, A., Fuhrman, I., Parr, A., Trutna, D., Xu, L., and Burba, G.: New Technology for Affordable and Deployable Direct Evapotranspiration Measurements, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-159, https://doi.org/10.5194/ems2023-159, 2023.

Coming from the German automotive industry, RAWLAB has developed a software-based approach that enables non-experts to work with measurement datasets from various sources, make them comparable, and applying complex data-analysis algorithms. Recently, the approach has been extended to include the field of scintillometry. This presentation will introduce the underlying data process and its possibilities resulting from the benefits of combining scintillometry expert knowledge with industry methods. These comprise the use of ASAM's (Association for Standardisation of Automation and Measuring Systems) ODS (Open Data Services) format to store and access any kind of data, as well as the feature to quickly publish any combination of results in automated reports available in e.g. .pdf, .docx, and .pptx formats. Furthermore, novel results and insights concerning the processing of scintillometer data will be discussed, as well as how the software can be used in the operational monitoring of diurnal evapotranspiration. Here we will focus on the use of spectrograms to observe the variation of scintillometer spectra throughout the day, newly derived coefficients for A_T and A_q valid for wavelengths between 0.3 - 3 mm, as well as on the preferred algorithms that allow users to get the best estimate for the total evapotranspiration over the course of a day. As an example, we will use two days of operational scintillometer data from the Lindenberg Observatory of the German Meteorological Service (DWD), Lindenberg, Germany, from June 2021 that were obtained during fair weather conditions with typical evapotranspiration summing up to about 3 mm per day.

How to cite: van Kesteren, B. and Beyrich, F.: Analysis of optical-microwave scintillometric measurements to determine evapotranspiration using RAWLAB’s data boosting and processing software, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-264, https://doi.org/10.5194/ems2023-264, 2023.

Accurate observations of atmospheric composition and exchange of greenhouse gases between the ecosystems and the atmosphere are critical for constraining climate models. Infrared gas analyzers (IRGA) using either broad band non-dispersive or narrow band tunable laser technologies are widely used for this purpose. Typically, such analyzers are installed on stationary meteorological towers over land; but an increasing number of systems are being deployed on mobile platforms and buoys to extend the spatial coverage and include measurements over water.  One technological challenge is that the motion of the platform influences the gas concentration measurements. Empirical correction methods have been proposed, but their universality is limited because the source of these sensor-related effects and their underlining mechanisms have not been understood. In this study we identified the dominant source of the error: orientation-dependent temperature stabilization of the thermoelectrically cooled infrared detector. To further investigate this hypothesis and gain insights to a solution, a new prototype closed-path IRGA with an improved infrared detector was developed. In the study, we compared the performance of the prototype to standard models of commercially available IRGA measuring CO2 and H2O.  Tilt experiments with side-by-side mounted IRGAs were first conducted on a controlled laboratory platform with independent pitch and roll axes. Over the ±30° range of angular position, the orientation-correlated errors were reduced by a factor of 4 to 10 on CO2 and a factor of 2 to 8 on H2O. Subsequent testing was performed duplicating realistic buoy motion in a deep-water tank with typical at-sea combined pitch and roll motion. In these tests, improvements in the measurement errors were similar to the laboratory experiments. Implications for the correction of past field measurements and insights for further sensor optimization and system improvements are discussed.

How to cite: Bogoev, I., Vandemark, D., Miller, S., Emond, M., Covert, J., and Shellito, S.: Improvements in infrared gas analyzers for measuring atmospheric gases on moving platforms, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-59, https://doi.org/10.5194/ems2023-59, 2023.

Doppler lidar systems are nowadays widely used for measuring the 3D wind vector within the atmospheric boundary layer (ABL). Different systems tailored towards different fields of application are commercially available. The WindRanger® is a compact, cost-effective and easy-to-use FMCW lidar for vertical wind profiling across the lowest 200 m metres above ground. It performs continuous velocity-azimuth-display scans of the laser beam at a zenith angle of 10 degrees.

To assess the performance of this instrument, a WindRanger® was operated at the boundary layer field site (in German: Grenzschichtmessfeld, GM) Falkenberg of the Deutscher Wetterdienst (DWD) over a period of 13 months. We have compared the wind measurements with this instrument at a height of 90 m above ground versus sonic data collected at the 99m-tower and (for a sub-period) versus lidar wind data obtained with a pulsed Doppler lidar Streamline (Halo Photonics). Limitations of the WindRanger® measurements occurred in connection with precipitation and with low cloud base heights such that the data had to be filtered accordingly. The comparison provided RMSD values around 0.4 ms⁻¹ for the wind speed and < 5° for the wind direction (after removing a bias due to improper alignment towards North).  

The WindRanger® allows for a time resolution of 0.5 s for one complete scan cycle. This lead us to investigate the possibility to derive wind gusts from the high-resolution time series. We found, however, that the wind speed from single-scan data exhibits a high variation throughout the day and derived gusts exceed the values determined from both the sonic and the Streamline Doppler lidar wind data in the convective boundary layer. This result is attributed to the small zenith angle (10 deg); this implies that the retrieved radial velocity values basically represent the vertical wind vector component which is typically characterized by strong fluctuations under convective conditions.

How to cite: Bohne, C., Beyrich, F., Detring, C., Kirtzel, H.-J., and Peters, G.: Results from a one-year test of the WindRanger® Doppler Lidar at GM Falkenberg, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-391, https://doi.org/10.5194/ems2023-391, 2023.

Correlating Lidar range performance with atmospheric condition parameters

Cristina Benzo, Ludovic Thobois, Maxime Hervo

Lidars have been increasingly integrated in various applications for its unique ability to measure continuously along multiple range gates for several kilometers. Lidars provide a significant advantage in meteorological networks as it extends beyond the measurement range of an anemometer to continually acquire wind speeds all throughout the boundary layer. Other applications such as wind field measurements for wind farm preventative energy management or airport shear detection highly depend on a lidar’s range of measurement to accurately visualize and forecast critical changes in wind speed. The ability of a lidar to measure several kilometers provides a unique advantage, yet the precise distance of its range capability greatly depends on atmospheric conditions. As a remote sensor, the performance of the return signal depends on the state of the atmosphere, which is based on extinction, backscatter, temperature, and more. Though a lidar range performance can be physically defined based on its signal processing qualities, the precise relationship of lidar range performance and atmospheric conditions is still unknown. Thus, this study aims to clarify and quantify this atmospheric relationship.

This study aims to rank the most impactful environmental variables on lidar range performance based on different regression and predictor techniques, as well as provide a first attempt at modelling range performance using machine learning and these environmental parameters. The variables considered in this analysis are lidar range, visibility, backscatter, PM2.5, relative humidity, AOD, temperature, and hour of the day.

The methods used in this analysis to determine correlation included a binned regression technique, to f-test statistical testing, and a random forest machine modeling technique. The binned regression technique was conducted by binning both the range and environmental variables to eliminate noisy conditions, visualize averaged patterns of range performance and environmental conditions, and conduct a regression fit to define the pattern between the two. The F-test provides a level of significance to each variable’s influence on range. Finally, a random forest model was trained and tested to predict lidar range performance based on several atmospheric measurements. Though lidar performance is not solely based on atmospheric conditions, the results showed promise and potential to combine with a physics-based model to account for overfitting and improve the loss function.

The results of the study yielded greater insights into the relationship between range and several atmospheric variables, as well as potential into how lidar range could be modelled based on environmental variable measurements. Backscatter and extinction demonstrated the highest impact on range performance across all methods applied, which follows the physical properties of the lidar’s carrier-to-noise ratio. With further development, predicting a lidar’s range performance could help users to plan and predict their measurement acquisition more efficiently.

How to cite: Benzo, C., Thobois, L., Hervo, M., and Toupoint, C.: Correlating Lidar range performance with atmospheric condition parameters, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-112, https://doi.org/10.5194/ems2023-112, 2023.

Doppler lidar systems scanning with a Velocity Azimuth Display (VAD) configuration are commonly used to determine profiles of wind speed and direction in the Atmospheric Boundary Layer (ABL, e.g. Päschke et al., 2015). In addition to the mean profile, short-term fluctuations of the wind, such as those that occur in connection with wind gusts, are of great interest and practical relevance.

For Doppler lidar systems of the type “Streamline” (Halo Photonics) we defined and tested a scan configuration which appears suitable for the derivation of wind gusts. In particular, a conical scan mode is used and performed as a so-called fast continuous scan mode (fast CSM) that allows with 3.4s a comparably fast duration for one single conical scan with 10-11 beam directions. Such a fast scan is required to measure wind gusts according to the widely accepted definition of a wind gust (3s moving average; WMO (2018)).

This special configuration introduces challenges to the data processing. Based on the fixed laser pulse repetition rate (10 kHz) of the lidar system comparatively few laser pulses are forming one measurement beam which in turn affect the quality of the radial velocity estimates. For that reason, classical approaches for data filtering (signal-to-noise thresholding, consensus filtering) are not always suitable. We therefore developed an alternative method for processing the raw lidar data.

Measurements from a one-year test operation of a Streamline Doppler lidar in the fast CSM at the boundary layer field site (GM) Falkenberg of the German Meteorological Service (DWD) were used to derive both the mean wind vector and the maximum wind gust for 10-minute averaging intervals. The results were compared with sonic measurements at 90m height. We obtained a very good correlation and RMSD values of ~0.3m/s for the mean wind speed and ~0.64m/s for the wind gusts. Similar results were obtained during a 4-weeks campaign at the “Hamburg Weather Mast” at larger heights (175m and 250m).

Besides these statistical results we will show examples of the gust detection for different weather situations (thunderstorm with cold pool, frontal passage, storm depression, convective gustiness) with particular emphasis on the vertical gust propagation.

World Meteorological Organization (WMO) (2018): Measurement of surface wind. In Guide to Meteorological Instruments and Methods of Observation, Volume I -Measurement of Meteorological Variables, No.8: 196–213, URL:https://library.wmo.int/index.php?lvl=notice_display&id=12407#.ZD7G0c7P1aS (accessed April 2023)

Päschke, E., Leinweber, R., and Lehmann, V. (2015): An assessment of the performance of a 1.5 μm Doppler lidar for operational vertical wind profiling based on a 1-year trial, Atmos. Meas. Tech., 8, 2251–2266, https://doi.org/10.5194/amt-8-2251-2015

How to cite: Detring, C., Päschke, E., Kayser, M., Leinweber, R., and Beyrich, F.: Deriving wind gusts based on Doppler lidar measurements using a fast continuous scan mode, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-570, https://doi.org/10.5194/ems2023-570, 2023.

Ground-based microwave radiometers (MWRs) operating in the K-band and V-band frequency ranges (22 – 32 GHz and 51 – 58 GHz) are increasingly used for acquiring temperature profiles (T) and coarse humidity profiles (H) of the troposphere. These instruments measure microwave radiances, expressed as brightness temperatures (TB), in zenith and other angles over a region with a radius of approximately 10 km. Those measured TBs are used to derive profiles. Ground-based MWRs are also highly reliable instruments for measuring integrated water vapor (IWV) and liquid water path (LWP), with uncertainties below 0.5 kg/m2 and 20 g/m2, respectively. Zenith observations provide these variables with high temporal resolution (up to 1 second), while elevation scans offer the capability to obtain more precise temperature profiles close to the surface and evaluate horizontal water vapor and cloud inhomogeneities.

Two years ago, the E-PROFILE program has initiated a business case proposal that was accepted by EUMETNET to offer continuous MWR data to the European meteorological services for boundary layer monitoring and assimilation in numerical weather prediction (NWP) models. Additionally, the European Research Infrastructure for the observation of Aerosol, Clouds, and Trace gases ACTRIS and the European COST action PROBE (PROfiling the atmospheric Boundary layer at European scale) are presently committed to establishing continent-wide quality and observation standards for MWR networks for research and NWP applications.

For all that it is important to provide an estimate of all the uncertainties of scanning MWR measurements. When installing a MWR, it has to be kept in mind that measurement uncertainties due to the instrument setup and originating from external sources can have an impact on observations and the quality of the obtained atmospheric profiles. Therefore, identifying and coping with these kinds of errors is one important part of the quality control, especially while searching for a suitable measurement location with minimum disturbances. We will present the impact of the following measurement uncertainties – namely (1) physical obstacles in line of sight of the instrument, (2) pointing errors or a tilt of the instrument, (3) horizontal inhomogeneities of the atmosphere, and (4) radio frequency interference (RFI) – and give recommendations on how to set-up a MWR accordingly.

How to cite: Böck, T., Pospichal, B., and Löhnert, U.: Measurement uncertainties of scanning microwave radiometers and their influence on temperature profiling, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-484, https://doi.org/10.5194/ems2023-484, 2023.

Exchange and transport processes in the atmospheric boundary layer (ABL) are driven by turbulence on a wide range of scales. Atmospheric turbulence is also a critical parameter for the determination of wind loads on structures such as wind turbines. Measuring turbulence with single point measurements requires assumptions about the stationarity, isotropy and homogeneity of the flow. The same applies if turbulence is retrieved from remote sensing instruments such as lidars. It is however well known that realistic turbulence does appear in more complex three-dimensional structures. This is the case in the ABL in stable and convective regimes, but even more so in complex terrain flow or in disturbed flow such as in the wake of wind turbines.
Without the infrastructure of meteorological masts and above applicable heights for such masts, in-situ point measurements of the three-dimensional wind vector are hardly available. We present a system to achieve simultaneous spatial measurements with a fleet of multirotor unmanned aircraft systems (UAS). The major benefit of this approach is, that true simultaneous measurements can be obtained without the need of expensive infrastructure. The SWUF-3D (Simultaneous Wind measurement with Unmanned Flight systems in 3D)  fleet was first deployed at the Meteorological Observatory Lindenberg - Richard Aßmann-Observatory (MOL-RAO) of DWD in association to the FESSTVaL campaign. With more than 1000 single flights, the system was validated against sonic anemometers at the 99-m mast in 2020 and 2021 and was able to provide reliable measurements of the wind vector with a RMSE below 0.3 m/s. We showed that turbulent eddies can be resolved with a time resolution of up to 2~Hz, unless the overall TKE level is below the noise threshold of the UAS measurements, which can be the case in stable ABL conditions. The results are verified by measurements in the wind tunnel of the University Oldenburg with an active turbulence grid under laboratory conditions in 2022. First measurements in the near wake of a wind turbine were also conducted in 2022. 
Additionally to the wind vector estimation, pressure, temperature and humidity sensors are carried by each UAS. Most recently, a fine-wire resistance thermometer was added to the setup, which measuring temperature much faster than with standard sensors. Fast response measurements of temperature and vertical wind allow the calculation of sensible heat flux additionally to the Reynolds stresses.
Within the project ESTABLIS-UAS (Exposing Spatio-temporal structures of Turbulence in the ABL with In-Situe Measurements by UAS, funded by the European Union), the SWUF-3D fleet will be enhanced to allow operation in larger areas and in complex terrain. A fleet of up to 100 UAS shall be deployed during TEAMx (Multi-scale transport and exchange processes in the atmosphere over mountains – programme and experiment) in 2025.

How to cite: Wildmann, N., Kistner, J., and Alexa, A.: Spatio-temporal measurements of turbulence in the ABL with a fleet of small uncrewed aircraft systems, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-444, https://doi.org/10.5194/ems2023-444, 2023.

In this study we introduce four Distributed Temperature Sensing (DTS) set-ups deployed at an irrigated alfalfa field site (La Cendrosa) as part of the LIAISE field campaign during 15-30 July 2021 in the north-east of Spain.  The DTS technique relies on the temperature dependence of Raman backscattering of light in a fibre optic cable. DTS provides spatially distributed temperature data over time. The type of profile (horizontal vs vertical), spatial- and temporal resolution and distance covered depend on the measurement configuration. To observe land-atmosphere interactions, we installed four set-ups in the LIAISE campaign, each of which focus on a different aspect.

We deployed a 1.6 mm diameter fibre covering a total distance of 600 m, which measured temperature at 5 s and 25.4 cm resolutions. In this continuous cable we included three DTS set-ups: 1) a surface layer profile between 1.6 - 40 m with a 25.4 cm vertical resolution, 2) a canopy profile averaged horizontally over 2.5 m with cables at 8 vertical levels between 0 - 1 m height inside of the rapidly-growing alfalfa and 3) a soil profile between -0.5 - 0 m with a vertical resolution of 1.25 cm; the enhanced spatial resolution was obtained by winding the cable onto a coil that was installed in the soil. An overview of these measurements is given, with an emphasis on factors limiting accuracy and on potential use in further research.

A fourth set-up was a so-called “turbulence harp”, which used a thinner and faster optical cable (0.5 mm) over a horizontal path of 70 m, measuring at four heights between 0.40 m and 2.05 m. Measurements were made at 1 Hz and 12.7 cm resolutions and a turbulent temperature spectrum was resolved up to 0.15 Hz. From this set-up, turbulence intensity was expressed in terms of the structure parameter of temperature (C_T²). We estimated C_T² both from the temperature time series along the DTS cables, as well as, and this is a novel approach, from the spatial temperature series over the DTS cable. The spatially determined structure parameter correlated with a sonic anemometer C_T² estimate, with a correlation coefficient of 0.88.

This work outlines the potential for using DTS in land-atmosphere interaction campaigns and provides a first step towards using DTS in capturing turbulent information along a spatial temperature series. 

How to cite: Vis, G., Hartogensis, O., ten Veldhuis, M.-C., and Coenders, M.: Spatial temperature measurements at the land-air interface using Distributed Temperature Sensing, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-603, https://doi.org/10.5194/ems2023-603, 2023.

The horizontal resolution of weather models is increasing, which demands a careful consideration of momentum and energy transport carried across different scales. Deep convective transport and even shallow convective transport, which were previously parameterized, are now resolved, while turbulence remains parameterized. Can observations help constrain the transport by turbulence, coherent structures associated with convection and mesoscale circulations coupled to organized cloud systems?

Using a novel experimental setup for deriving high-resolution continuous wind profiles across the boundary layer, our objective is to provide a fresh view on the variability in horizontal and vertical wind in the presence of a range of (shallow) cloud systems over land, as well as to derive the wind variance and momentum fluxes, and a quantitative assessment of the relevant scales.

The experimental dataset is collected during the Tracing Convective Momentum Transport in Complex Cloudy Atmospheres experiment (CMTRACE). The field campaign occurred at the experimental Cabauw site (The Netherlands) between 13.09.2021 and 03.10.2021 and between 16.05.2022 and 13.06.2022. For this experiment, a cloud radar and wind lidar were operated at 75 degrees elevation, providing horizontal and vertical wind observations within and below the cloud layer. The combined lidar-radar's wind profiles have a vertical resolution of 50 m and a temporal resolution of ~1.5 minutes (which is representative of a horizontal scale of 450 - 1800 m). During CMTRACE, a large variety of cloud regimes were sampled, from non-precipitating shallow convection to deep convective clouds and stratiform clouds.

The observations reveal both coherent thermals (up and downdrafts) and mesoscale divergence and convergence patterns. The scale growth of horizontal momentum variance and flux is well explained by vertical velocity variance, whereby larger vertical velocity variance corresponds to a larger contribution of scales < 35 km to total momentum variance and flux. Additionally, precipitation is shown to separate days on which larger mesoscales contribute to horizontal momentum flux, and the presence of larger cloud structures is confirmed using cloud spatial statistics as viewed from satellite.  In an outlook, the representation of these different flows in large-eddy simulation and regional weather hindcasts from the Dutch weather model HARMONIE is evaluated.

How to cite: Dias Neto, J. and Nuijens, L.: Boundary layer coherent structures and circulations viewed through collocated wind lidar and cloud radar profiling, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-447, https://doi.org/10.5194/ems2023-447, 2023.

The Tropical Cyclone Boundary Layer (TCBL) is uniquely favorable for the formation of highly asymmetric coherent structures called roll-vortices. They are kilometer-scale eddies that are aligned in the mean tangential wind direction and are generally associated with a combination of shear and convective instability. Roll-vortices can cause periodic enhancements of winds as well as surface fluxes and may assist the intensification process via vertical transport of tangential momentum. Furthermore, the up-gradient transfer of surface heat and momentum fluxes associated with roll-vortices can energize the large-scale motions, possibly resulting in an increased convective activity. It is therefore important to understand and quantify the effects of roll-vortices in setting the overall TCBL structure as well as near-surface winds.

Synthetic Aperture Radars onboard low-earth orbit (LEO) satellites such as Sentinel-1A/B and RadarSat-2 have often been used to identify TCBL roll-vortices. Based on the positive correlation between microwave backscattering and sea surface roughness, sea surface wind speed can be retrieved at high spatial resolution (1–3 km), without any saturation for high wind speed. However, the spatial distribution of roll-vortices in the TCBL and their subsequent impact on the vertical momentum and enthalpy fluxes are not well understood.  In this study, we use standard two-dimensional spectral analysis to detect roll-vortices in SAR-observed winds over multiple tropical cyclones (TCs) and use TC-relative composites to analyze their spatial distributions. We will also study the vertical wind and thermodynamic structures in the vicinity of SAR-observed roll-vortices using collocated aircraft observations whenever available. This may also allow us to extract empirical relationships between the roll-averaged vertical profiles of near-surface fluxes and maximum near-surface winds.

How to cite: Dey, I. and O'Neill, M.: Observing the effects of roll-vortices on the Tropical Cyclone Boundary Layer (TCBL) using Synthetic Aperture Radars (SAR), EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-390, https://doi.org/10.5194/ems2023-390, 2023.

The advancements in microelectronics, high-frequency electronics, and FPGA enabled the development and further availability of software-defined receivers (SDR). This article deals with the possibilities of using the sources of electromagnetic energy for the detection of the hydrometeors in the lowest layer of the atmosphere in real time. Our effort was targeted toward the space and time localization of precipitation and its intensity by using frequencies around one GHz.

Electromagnetic signal attenuation by water vapor and by precipitation either in liquid or solid form in these bands is immeasurable and it is basically lost in the noise. The use of signal attenuation by the liquid precipitation, typically by using the remote directional connection, is effective in microwave bands over 10 GHz.

Refractivity is the physical value that impacts electromagnetic signal penetration through the atmosphere. It depends on the air pressure, temperature, and saturated water vapor, and from the point of view of electromagnetic signal propagation it represents the properties of the material environment which influences its speed and dispersion. Determination of the refractivity value is a quite complicated process. It requires sophisticated instrumentation based on highly accurate time normal. This work is bringing a method that is using atmospheric refractivity changes (its gradient) between different trajectories along which electromagnetic energy is spread from the broadcaster to a simple antenna system. A coherent SDR receiver is used for the evaluation of time delays between the signals coming to different antennas. The time shifts are converted to the frequency changes towards the frequency at which the observation was done. An advantage of this method comes from the fact that it does not depend on the signal strength until it is available. It is a fully passive method using external sources of the electromagnetic signal and the signal does not need to be decoded. Phase difference between the signals is related to the frequency of the source signal and depends on the properties of the atmosphere.

Performed experimental measurements recognized that the evaluation of the phase changes by a coherent receiver is correlated with different atmospheric phenomena and showed the possibility to detect them. The phase change reacted to different atmospheric phenomena mostly, but not exclusively, related to hydrometeors. Detection of the local as well as frontal showers and thunderstorms with high-intensity precipitation was clearly shown as well as the relaxation of the atmospheric humidity after the time-limited precipitation. Further to that the method reacts to atmospheric turbulence and to the thermal inversion process.

The results come from a certain number of time-limited experiments. Continual monitoring in selected localities is envisaged in close future.

How to cite: Fabo, P., Nejedlik, P., Kuba, M., and Onderka, M.: Phase difference method at UHF frequency band for hydrometeor detection, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-168, https://doi.org/10.5194/ems2023-168, 2023.

Raindrop size distribution (DSD) is an important parameter in rainfall research and can be used for quantitative precipitation estimation (QPE) in meteorology and hydrology. DSD also improves the understanding of the uncertainty of cloud microphysical processes (CMPs) such as ice-based and warm rain growth during climate change. Changes in CMPs impact the generation of precipitation. However, the estimation of CMPs based on in situ observation is difficult because of the complexity of microphysics processes, and most previous studies on the CMP involved approximations to predict the types of microphysical processes affecting precipitation generation based on in situ observations performed in real-time. Therefore, a simple method was developed to understand CMPs of precipitation generation using a conceptual model of CMPs and in situ observation DSD data. Previously observed DSD parameters and a CMP conceptual model of the DSD observation-based microphysical process were employed. As case studies, DSD observation data obtained in Korea and East Asia were applied to estimate the CMPs. For example, the major CMP of megacities was vapor deposition in Beijing (< 1 mm h⁻¹) and Seoul (< 5 mm h⁻¹), as the strong updraft of the urban heat island effect in megacities results in increased liquid water content, leading to the formation of large number of supersaturated clouds at higher altitudes.  In the example case, vapor deposition is a process where water vapor condenses directly into ice crystals or water droplets without passing through an intermediate liquid phase.  So, the urban heat island effect refers to an urban area that is significantly warmer than its surrounding rural areas due to human activities. 

Acknowledgement : This research has been supported by the "Research on Weather Modification and Cloud Physics"(KMA2018-00224) project of NIMS/KMA.

How to cite: Cha, J. W.: Analysis of Rain Drop Size Distribution to classify  the Precipitation Process using a Cloud Microphysics Conceptual Model and In Situ Measurement, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-86, https://doi.org/10.5194/ems2023-86, 2023.