Disentangling the contributions of orographic waves, boundary-layer coupling, and aerosol to the occurrence of ice in mixed-phase clouds

2021 ◽  
Author(s):  
Martin Radenz ◽  
Patric Seifert ◽  
Johannes Bühl ◽  
Holger Baars ◽  
Ronny Engelmann ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Southern Ocean ◽  
Eastern Mediterranean ◽  
Microwave Radiometer ◽  
Ice Formation ◽  
Apparent Lack ◽  
Liquid Saturation ◽  
Northern Hemispheric ◽  
Surface Coupling

<p>We will present a study on the impacts of orographic waves, surface coupling, and aerosol load on the frequency of heterogeneous ice formation in stratiform clouds using ground-based remote-sensing observations. Disentangling the convoluted effects of vertical motions and aerosols is critical for the understanding of heterogeneous ice formation and requires comprehensive observations. For the study, multi-year datasets from Punta Arenas (53.1°S 70.9°W, Chile, >2 years) and the northern hemispheric sites of Leipzig (51.4°N 12.4°E, Germany, 2.6 years) and Limassol (34.7°N 33.0°E, Cyprus, 1.5 years) were obtained by the same set of ground-based instruments (35-GHz cloud radar, Raman polarization lidar, 14-channel microwave radiometer, Doppler lidar, and disdrometer). The datasets at Limassol and Punta Arenas resemble the first multi-year ground-based remote-sensing datasets in the Eastern Mediterranean and in the western part of the Southern Ocean, respectively.</p> <p>The cloud properties were extracted from the synergistic dataset and the following key results on the efficiency of heterogeneous ice formation emerged:<br />The apparent lack of ice forming clouds at Punta Arenas below -15 <strong>°</strong>C can be related to orographic gravity waves, which allow persistent liquid saturation. These clouds could be identified by the autocorrelation function of the in-cloud vertical air velocity. Additionally, a correlation between the surface-coupling of a cloud and the likelihood of ice formation was found for Punta Arenas and Leipzig. At T>-10°C clouds coupled to the aerosol-rich boundary layer, were found to contain ice more frequently. Taking both effects into account, free-tropospheric, fully turbulent clouds at Punta Arenas form ice less frequently than their northern-hemispheric counterparts. This difference is linked to the lower abundance of INP in the free troposphere over the Southern Ocean.</p>

scholarly journals Assessing the accuracy of microwave radiometers and radio acoustic sounding systems for wind energy applications

2016 ◽  
Author(s):  
Laura Bianco ◽  
Katja Friedrich ◽  
James Wilczak ◽  
Duane Hazen ◽  
Daniel Wolfe ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Relative Humidity ◽  
Mean Absolute Error ◽  
Microwave Radiometer ◽  
Absolute Error ◽  
Acoustic Sounding ◽  
Energy Applications ◽  
Virtual Temperature ◽  
Microwave Radiometers

Abstract. To assess current remote-sensing capabilities for wind energy applications, a remote-sensing system evaluation study, called XPIA (eXperimental Planetary boundary layer Instrument Assessment), was held in the spring of 2015 at NOAA’s Boulder Atmospheric Observatory (BAO) facility. Several remote-sensing platforms were evaluated to determine their suitability for the verification and validation processes used to test the accuracy of numerical weather prediction models. The evaluation of these platforms was performed with respect to well-defined reference systems: the BAO’s 300-m tower equipped at 6 levels (50, 100, 150, 200, 250, and 300 m) with 12 sonic anemometers and 6 temperature and relative humidity sensors; and approximately 60 radiosonde launches. In this study we first employ these reference measurements to validate temperature profiles retrieved by two co-located microwave radiometers, as well as virtual temperature measured by co-located wind profiling radars equipped with radio acoustic sounding systems. Results indicate a mean absolute error in the temperature retrieved by the microwave radiometers below 1.5 °C in the lowest 5 km of the atmosphere, and a mean absolute error in the virtual temperature measured by the radio acoustic sounding systems below 0.8 °C in the layer of the atmosphere covered by these measurements (up to approximately 1.6–2 km). We also investigated the benefit of the vertical velocity applied to the speed of sound before computing the virtual temperature by the radio acoustic sounding systems. We find that using this correction frequently increases the RASS error, and that it should not be routinely applied to all data. Water vapor density profiles measured by the MWRs were also compared with similar measurements from the soundings, showing the capability of MWRs to follow the vertical profile measured by the sounding, and finding a mean absolute error below 0.5 g m−3 in the lowest 5 km of the atmosphere. However, the relative humidity profiles measured by the microwave radiometer lack the high-resolution details available from radiosonde profiles. An encouraging and significant finding of this study was that the coefficient of determination between the lapse rate measured by the microwave radiometer and the tower measurements over the tower levels between 50 and 300 m ranged from 0.76 to 0.91, proving that these remote-sensing instruments can provide accurate information on atmospheric stability conditions in the lower boundary layer.

scholarly journals Studying turbulence by remote sensing systems during slope-2016 campaign

2018 ◽  
Vol 176 ◽  
pp. 06010
Author(s):  
Gregori de A. Moreira ◽  
Juan L. Guerrero-Rascado ◽  
Jose A. Benavent-Oltra ◽  
Pablo Ortiz-Amezcua ◽  
Roberto Róman ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Microwave Radiometer ◽  
Passive Microwave ◽  
Doppler Lidar ◽  
Sensing Systems ◽  
Remote Sensing Systems ◽  
Lowermost Part

The Planetary Boundary Layer (PBL) is the lowermost part of the troposphere. In this work, we analysed some high order moments and PBL height detected continuously by three remote sensing systems: an elastic lidar, a Doppler lidar and a passive Microwave Radiometer, during the SLOPE-2016 campaign, which was held in Granada from May to August 2016. This study confirms the feasibility of these systems for the characterization of the PBL, helping us to justify and understand its behaviour along the day.

scholarly journals Assimilation of Surface-Based Boundary Layer Profiler Observations during a Cool-Season Weather Event Using an Observing System Simulation Experiment. Part I: Analysis Impact

2011 ◽  
Vol 139 (8) ◽  
pp. 2309-2326 ◽  
Author(s):  
Jason A. Otkin ◽  
Daniel C. Hartung ◽  
David D. Turner ◽  
Ralph A. Petersen ◽  
Wayne F. Feltz ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Simulation Experiment ◽  
System Simulation ◽  
Microwave Radiometer ◽  
Lower Troposphere ◽  
Moisture Profile ◽  
Wind Profiles ◽  
Observing System Simulation Experiment ◽  
The Impact

AbstractIn this study, an Observing System Simulation Experiment was used to examine how the assimilation of temperature, water vapor, and wind profiles from a potential array of ground-based remote sensing boundary layer profiling instruments impacts the accuracy of atmospheric analyses when using an ensemble Kalman filter data assimilation system. Remote sensing systems evaluated during this study include the Doppler wind lidar (DWL), Raman lidar (RAM), microwave radiometer (MWR), and the Atmospheric Emitted Radiance Interferometer (AERI). The case study tracked the evolution of several extratropical weather systems that occurred across the contiguous United States during 7–8 January 2008. Overall, the results demonstrate that using networks of high-quality temperature, wind, and moisture profile observations of the lower troposphere has the potential to improve the accuracy of wintertime atmospheric analyses over land. The impact of each profiling system was greatest in the lower and middle troposphere on the variables observed or retrieved by that instrument; however, some minor improvements also occurred in the unobserved variables and in the upper troposphere, particularly when RAM observations were assimilated. The best analysis overall was achieved when DWL wind profiles and temperature and moisture observations from the RAM, AERI, or MWR were assimilated simultaneously, which illustrates that both mass and momentum observations are necessary to improve the analysis accuracy.

scholarly journals Hemispheric contrasts in ice formation in stratiform mixed-phase clouds: disentangling the role of aerosol and dynamics with ground-based remote sensing

2021 ◽  
Vol 21 (23) ◽  
pp. 17969-17994
Author(s):  
Martin Radenz ◽  
Johannes Bühl ◽  
Patric Seifert ◽  
Holger Baars ◽  
Ronny Engelmann ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Gravity Wave ◽  
Detection Threshold ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
Ice Formation ◽  
Absolute Difference ◽  
Optical Parameters ◽  
Mixed Phase Clouds

Abstract. Multi-year ground-based remote-sensing datasets were acquired with the Leipzig Aerosol and Cloud Remote Observations System (LACROS) at three sites. A highly polluted central European site (Leipzig, Germany), a polluted and strongly dust-influenced eastern Mediterranean site (Limassol, Cyprus), and a clean marine site in the southern midlatitudes (Punta Arenas, Chile) are used to contrast ice formation in shallow stratiform liquid clouds. These unique, long-term datasets in key regions of aerosol–cloud interaction provide a deeper insight into cloud microphysics. The influence of temperature, aerosol load, boundary layer coupling, and gravity wave motion on ice formation is investigated. With respect to previous studies of regional contrasts in the properties of mixed-phase clouds, our study contributes the following new aspects: (1) sampling aerosol optical parameters as a function of temperature, the average backscatter coefficient at supercooled conditions is within a factor of 3 at all three sites. (2) Ice formation was found to be more frequent for cloud layers with cloud top temperatures above -15∘C than indicated by prior lidar-only studies at all sites. A virtual lidar detection threshold of ice water content (IWC) needs to be considered in order to bring radar–lidar-based studies in agreement with lidar-only studies. (3) At similar temperatures, cloud layers which are coupled to the aerosol-laden boundary layer show more intense ice formation than decoupled clouds. (4) Liquid layers formed by gravity waves were found to bias the phase occurrence statistics below -15∘C. By applying a novel gravity wave detection approach using vertical velocity observations within the liquid-dominated cloud top, wave clouds can be classified and excluded from the statistics. After considering boundary layer and gravity wave influences, Punta Arenas shows lower fractions of ice-containing clouds by 0.1 to 0.4 absolute difference at temperatures between −24 and -8∘C. These differences are potentially caused by the contrast in the ice-nucleating particle (INP) reservoir between the different sites.

scholarly journals The COTUR project: Remote sensing of offshore turbulence for wind energy application

2021 ◽  
Author(s):  
Etienne Cheynet ◽  
Martin Flügge ◽  
Joachim Reuder ◽  
Jasna B. Jakobsen ◽  
Yngve Heggelund ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Surface Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbines ◽  
Microwave Radiometer ◽  
Wind Load ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Sensing Technology

Abstract. The paper presents the measurement strategy and dataset collected during the COTUR (COherence of TURbulence with lidars) campaign. This field experiment took place from February 2019 to April 2020 on the southwestern coast of Norway. The coherence quantifies the spatial correlation of eddies and is little known in the marine atmospheric boundary layer. The study was motivated by the need to better characterize the lateral coherence, which partly governs the dynamic wind load on multi-megawatt offshore wind turbines. During the COTUR campaign, the coherence was studied using land-based remote sensing technology. The instrument setup consisted of three long-range scanning Doppler wind lidars, one Doppler wind lidar profiler and one passive microwave radiometer. Both the WindScanner software and Lidar Planner software were used jointly to simultaneously orient the three scanner heads into the mean wind direction, which was provided by the lidar wind profiler. The radiometer instrument complemented these measurements by providing temperature and humidity profiles in the atmospheric boundary layer. The preliminary results show an undocumented variation of the lateral coherence with the distance from the coast. The scanning beams were pointed slightly upwards to record turbulence characteristics both within and above the surface layer, providing further insight on the applicability of surface-layer scaling to model the turbulent wind load on offshore wind turbines.

An evaluation of kilometre scale ICON simulations of mixed-phase stratocumulus over the Southern Ocean during CAPRICORN

2021 ◽  
Author(s):  
Veeramanikandan Ramadoss ◽  
Kevin Pfannkuch ◽  
Alain Protat ◽  
Yi Huang ◽  
Steven Siems ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Southern Ocean ◽  
Climate Models ◽  
Weather Prediction ◽  
Precipitation Amount ◽  
Mixed Phase ◽  
Atmospheric Composition ◽  
Wave Radiation ◽  
Shallow Convection

<p>Stratocumulus (Sc) clouds cover between 25% to 40% of the mid-latitude oceans, where they substantially cool the ocean surface. Many climate models poorly represent these marine boundary layer clouds in the lee of cold fronts in the Southern Ocean (SO), which yields a substantial underestimation of the reflection of short wave radiation. This results in a positive mean bias of 2K in the SO. The representation of stratocumulus clouds, cloud variability, precipitation statistics, and boundary layer dynamics within the ICON-NWP (Icosahedral Nonhydrostatic – Numerical Weather Prediction) model at the km-scale is evaluated in this study over the SO.</p><p>Real case simulations forced by ERA5 are performed with a two-way nesting strategy down to a resolution of 1.2 km. The model is evaluated using the soundings, remote sensing and in-situ observations obtained during the CAPRICORN (Clouds, Aerosols, Precipitation, Radiation, and Atmospheric Composition over the Southern Ocean) field campaign that took place during March and April 2016. During two days (26<sup>th</sup> to 27<sup>th</sup> of March 2016), open-cell stratocumuli were continuously observed by the shipborne radars and lidars between 47<sup>o</sup>S 144<sup>o</sup>E and 45<sup>o</sup>S 146<sup>o</sup>E (South of Tasmania). Our simulations are evaluated against the remote sensing retrievals using the forward simulated radar signatures from PAMTRA (Passive and Active Microwave TRAnsfer).</p><p>The initial results show that the observed variability of various cloud fields is best captured in simulations where only shallow convection is parameterised at this scale. Furthermore, ICON-NWP captures the observed intermittency of precipitation, yet the precipitation amount is overestimated. We further analyse the sensitivity of the cloud and precipitation statistics with respect to primary and secondary ice-phase processes (such as Hallett–Mossop and collisional breakup) in ICON-NWP. Both processes have previously been shown to improve ice properties of simulated shallow mixed-phase clouds over the Southern Ocean in other models. </p>

scholarly journals Assimilation of Surface-Based Boundary Layer Profiler Observations during a Cool-Season Weather Event Using an Observing System Simulation Experiment. Part II: Forecast Assessment

2011 ◽  
Vol 139 (8) ◽  
pp. 2327-2346 ◽  
Author(s):  
Daniel C. Hartung ◽  
Jason A. Otkin ◽  
Ralph A. Petersen ◽  
David D. Turner ◽  
Wayne F. Feltz
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Microwave Radiometer ◽  
Moisture Flux ◽  
Ensemble Forecasts ◽  
Thermodynamic Structure ◽  
Critical Success ◽  
Object Based ◽  
Remote Sensing Systems ◽  
Wind Profiles

AbstractIn this study, atmospheric analyses obtained through assimilation of temperature, water vapor, and wind profiles from a potential network of ground-based remote sensing boundary layer profiling instruments were used to generate short-range ensemble forecasts for each assimilation experiment performed in Part I. Remote sensing systems evaluated during this study include the Doppler wind lidar (DWL), Raman lidar (RAM), microwave radiometer (MWR), and the Atmospheric Emitted Radiance Interferometer (AERI). Overall, the results show that the most accurate forecasts were achieved when mass (temperature and humidity profiles from the RAM, MWR, and/or AERI) and momentum (wind profiles from the DWL) observations were assimilated simultaneously, which is consistent with the main conclusion from Part I. For instance, the improved wind and moisture analyses obtained through assimilation of these observations contributed to more accurate forecasts of moisture flux convergence and the intensity and location of accumulated precipitation (ACPC) due to improved dynamical forcing and mesoscale boundary layer thermodynamic structure. An object-based verification tool was also used to assess the skill of the ACPC forecasts. Overall, total interest values for ACPC matched objects, along with traditional forecast skill statistics like the equitable threat score and critical success index, were most improved in the multisensor assimilation cases.

Atmospheric boundary layer parameters retrieval from Stepped Frequency Microwave Radiometer measurements in tropical cyclones

2020 ◽  
Author(s):  
Nikita Rusakov ◽  
Evgeny Poplavsky ◽  
Olga Ermakova ◽  
Yuliya Troitskaya ◽  
Daniil Sergeev ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Microwave Radiometer ◽  
Remote Sensing Data ◽  
Field Measurements ◽  
Radar Signal ◽  
Time And Space ◽  
Sensing Data ◽  
Radar Images

<p>Active microwave sensing using satellite instruments has great advantages, since in this range the absorption by clouds and atmospheric gases is noticeably reduced, it allows for round-the-clock and all-weather monitoring of the ocean. One of the main problems is concerned with obtaining the dependency between the RCS of radar signal scattered by the wavy water surface and the parameters of the atmospheric boundary layer in hurricane conditions. To obtain this dependence, we used field measurements of wind speed in a hurricane from falling NOAA GPS-sondes and SAR images from the Sentinel-1 satellite. However, there is the problem of correct collocation of remote sensing data with field measurements of the atmospheric boundary layer parameters, since they are separated in time and space. In this regard, the amount of data suitable for analysis is very limited, which forces us to look for new data sources for processing. A six-channel SFMR radiometer is also installed on board of NOAA research aircraft that measures the emissivity of the ocean surface beneath the aircraft. Thus, it becomes possible to relate the radiometric measurements of SFMR with the parameters of the atmospheric boundary layer in a tropical cyclone obtained from wind velocity profiles, since they are carried out as close as possible in time and space. Using this relation, the SFMR data and the hurricane radar images were analyzed together and an alternative method was found for constructing the dependence of the RCS on the parameters of the boundary layer.</p><p>This work was supported by the RFBR projects No. 19-05-00249, 19-05-00366, 18-35-20068 (remote sensing data analysis) and RSF No. 19-17-00209 (GPS-sondes data assimilation and processing).</p><p> </p>

An evaluation of kilometre scale ICON simulations of mixed-phase stratocumulus over the Southern Ocean during CAPRICORN

2021 ◽  
Author(s):  
Veeramanikandan Ramadoss ◽  
Kevin Pfannkuch ◽  
Alain Protat ◽  
Yi Huang ◽  
Steven Siems ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Southern Ocean ◽  
Climate Models ◽  
Weather Prediction ◽  
Precipitation Amount ◽  
Mixed Phase ◽  
Atmospheric Composition ◽  
Wave Radiation ◽  
Shallow Convection

<p>Stratocumulus (Sc) clouds cover between 25% to 40% of the mid-latitude oceans, where they substantially cool the ocean surface. Many climate models poorly represent these marine boundary layer clouds in the lee of cold fronts in the Southern Ocean (SO), which yields a substantial underestimation of the reflection of short-wave radiation. This results in a positive mean bias of 2 K in the SO. The representation of stratocumulus clouds, cloud variability, precipitation statistics, and boundary layer dynamics within the ICON-NWP (Icosahedral Nonhydrostatic – Numerical Weather Prediction) model at the km-scale is evaluated in this study over the SO.</p> <p><br />Real case simulations forced by ERA5 are performed with a two-way nesting strategy down to a resolution of 1.2 km. The model is evaluated using the soundings, remote sensing and in-situ observations obtained during the CAPRICORN (Clouds, Aerosols, Precipitation, Radiation, and Atmospheric Composition over the Southern Ocean) field campaign that took place during March and April 2016. During two days (26 and 27 March 2016), open-cell stratocumuli were continuously observed by the shipborne radars and lidars between 47<sup>o</sup>S 144<sup>o</sup>E and 45<sup>o</sup>S 146<sup>o</sup>E (South of Tasmania). Our simulations are evaluated against the remote sensing retrievals using the forward simulated radar signatures from PAMTRA (Passive and Active Microwave TRAnsfer).</p> <p><br />The initial results show that the observed variability of various cloud fields is best captured in simulations where only shallow convection is parameterised at this scale. Furthermore, ICON-NWP captures the observed intermittency of precipitation, yet the precipitation amount is overestimated. We further analyse the sensitivity of the cloud and precipitation statistics with respect to primary and secondary ice-phase processes (such as Hallett–Mossop and collisional breakup) in ICON-NWP. Both processes have previously been shown to improve ice properties of simulated shallow mixed-phase clouds over the Southern Ocean in other models.</p>

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