scholarly journals Why we need radar, lidar, and solar radiance observations to constrain ice cloud microphysics

2021 ◽  
Vol 14 (7) ◽  
pp. 5029-5047
Author(s):  
Florian Ewald ◽  
Silke Groß ◽  
Martin Wirth ◽  
Julien Delanoë ◽  
Stuart Fox ◽  
...  
Keyword(s):  
Water Content ◽  
Cloud Microphysics ◽  
Accurate Estimation ◽  
Crystal Shape ◽  
Radiative Effect ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Ice Water Content ◽  
Ice Water

Abstract. Ice clouds and their effect on earth's radiation budget are one of the largest sources of uncertainty in climate change predictions. The uncertainty in predicting ice cloud feedbacks in a warming climate arises due to uncertainties in measuring and explaining their current optical and microphysical properties as well as from insufficient knowledge about their spatial and temporal distribution. This knowledge can be significantly improved by active remote sensing, which can help to explore the vertical profile of ice cloud microphysics, such as ice particle size and ice water content. This study focuses on the well-established variational approach VarCloud to retrieve ice cloud microphysics from radar–lidar measurements. While active backscatter retrieval techniques surpass the information content of most passive, vertically integrated retrieval techniques, their accuracy is limited by essential assumptions about the ice crystal shape. Since most radar–lidar retrieval algorithms rely heavily on universal mass–size relationships to parameterize the prevalent ice particle shape, biases in ice water content and ice water path can be expected in individual cloud regimes. In turn, these biases can lead to an erroneous estimation of the radiative effect of ice clouds. In many cases, these biases could be spotted and corrected by the simultaneous exploitation of measured solar radiances. The agreement with measured solar radiances is a logical prerequisite for an accurate estimation of the radiative effect of ice clouds. To this end, this study exploits simultaneous radar, lidar, and passive measurements made on board the German High Altitude and Long Range Research Aircraft. By using the ice clouds derived with VarCloud as an input to radiative transfer calculations, simulated solar radiances are compared to measured solar radiances made above the actual clouds. This radiative closure study is done using different ice crystal models to improve the knowledge of the prevalent ice crystal shape. While in one case aggregates were capable of reconciling radar, lidar, and solar radiance measurements, this study also analyses a more problematic case for which no radiative closure could be achieved. In this case, collocated in situ measurements indicate that the lack of closure may be linked to unexpectedly high values of the ice crystal number density.

scholarly journals Why we need radar, lidar, and solar radiance observations to constrain ice cloud microphysics

2021 ◽  
Author(s):  
Florian Ewald ◽  
Silke Groß ◽  
Martin Wirth ◽  
Julien Delanoë ◽  
Stuart Fox ◽  
...  
Keyword(s):  
Water Content ◽  
Cloud Microphysics ◽  
Accurate Estimation ◽  
Crystal Shape ◽  
Radiative Effect ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Ice Water Content ◽  
Ice Water

Abstract. Ice clouds and their effect on Earth's radiation budget are one of the largest sources of uncertainty in climate change predictions. The uncertainty in predicting ice cloud feedbacks in a warming climate arises due to uncertainties in measuring and explaining their current optical and microphysical properties as well as from insufficient knowledge about their spatial and temporal distribution. This knowledge can be significantly improved by active remote sensing, which can help to explore the vertical profile of ice cloud microphysics, such as ice particle size and ice water content. This study focuses on the well-established variational approach VarCloud to retrieve ice cloud microphysics from radar-lidar measurements. While active backscatter retrieval techniques surpass the information content of most passive, vertically integrated retrieval techniques, their accuracy is limited by essential assumptions about the ice crystal shape. Since most radar-lidar retrieval algorithms rely heavily on universal mass-size relationships to parameterize the prevalent ice particle shape, biases in ice water content and ice water path can be expected in individual cloud regimes. In turn, these biases can lead to an erroneous estimation of the radiative effect of ice clouds. In many cases, these biases could be spotted and corrected by the simultaneous exploitation of measured solar radiances. The agreement with measured solar radiances is a logical prerequisite for an accurate estimation of the radiative effect of ice clouds. To this end, this study exploits simultaneous radar, lidar, and passive measurements made on board the German High Altitude and Long Range Research Aircraft. By using the ice clouds derived with VarCloud as an input to radiative transfer calculations, simulated solar radiances are compared to measured solar radiances made above the actual clouds. This radiative closure study is done using different ice crystal models to improve the knowledge of the prevalent ice crystal shape. While in one case aggregates were capable of reconciling radar, lidar, and solar radiance measurements, this study also analyses a more problematic case for which no radiative closure could be achieved. In this case, simultaneously acquired in-situ measurements could narrow this inability to an unexpected high ice crystal number concentration.

Evaluation of Collocated Measurements of Radar Reflectivity and Particle Sizes in Ice Clouds

2011 ◽  
Vol 50 (10) ◽  
pp. 2104-2119 ◽  
Author(s):  
Binod Pokharel ◽  
Gabor Vali
Keyword(s):  
Water Content ◽  
Particle Density ◽  
Radar Data ◽  
Precipitation Rate ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Sampling Locations ◽  
Ice Water Content ◽  
Particle Imaging ◽  
Ice Water

AbstractMeasured 94-GHz reflectivity in midlevel, stratiform ice clouds was compared with reflectivity calculated from size distributions determined with a particle imaging probe. The radar and the particle probe were carried on the same aircraft, the Wyoming King Air, ensuring close spatial correspondence between the two measurements. Good overall agreement was found within the range from −18 to +16 dBZ, but there is an important degree of scatter in the results. Two different assumptions about particle density led to calculated values that bracket the observations. The agreement found for reflectivity supports the use of the data for establishing relationships between the measured reflectivity and ice water content and between precipitation rate and reflectivity. The resulting equation for ice water content (IWC vs Z) agrees with the results of Liu and Illingworth within a factor of 2 over the range of overlap between the two datasets. The equation here reported for precipitation rate (PR vs Z) has a shallower slope in the power-law relationship than that reported by Matrosov as a consequence of sampling particles of greater densities. Because the radar and the particle probe were collocated on the same platform, errors arising from differences in sampling locations and volumes were minimized. Therefore it is concluded that the roughly factor-of-10 spread in IWC and in PR for given Z is, primarily, a result of variations in ice crystal shape and density. Retrievals of IWC and PR from cloud radar data can be expected to have that level of uncertainty.

scholarly journals Evidence for ice particles in the tropical stratosphere from in-situ measurements

2008 ◽  
Vol 8 (6) ◽  
pp. 19313-19355 ◽  
Author(s):  
M. de Reus ◽  
S. Borrmann ◽  
A. J. Heymsfield ◽  
R. Weigel ◽  
C. Schiller ◽  
...  
Keyword(s):  
Water Content ◽  
Size Distribution ◽  
Crystal Size ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Ice Water Content ◽  
Tropical Troposphere ◽  
Ice Crystal Size ◽  
Ice Water

Abstract. In-situ ice crystal size distribution measurements are presented within the tropical troposphere and lower stratosphere. The measurements were performed using a combination of a Forward Scattering Spectrometer Probe (FSSP-100) and a Cloud Imaging Probe (CIP) which were installed on the Russian high altitude research aircraft M55 "Geophysica" during the SCOUT-O3 campaign in Darwin, Australia. The objective of the campaign was to characterise the outflow of the Hector convective system, which appears on an almost daily basis during the pre-monsoon season over the Tiwi Islands, north of Darwin. In total 90 encounters with ice clouds, between 10 and 19 km altitude were selected from the dataset and were analysed. Six of these encounters were observed in the lower stratosphere, up to 1.4 km above the local tropopause, and were a result of overshooting convection. The ice crystals observed in the stratosphere comprise sizes up to 400 μm maximum dimension, include an ice water content of 0.1×10−3–1.7×10−3 g m−3 and were observed at ambient relative humidities (with respect to ice) between 75 and 157%. Three modal lognormal size distributions were fitted to the average size distributions for different potential temperature intervals, showing that the shape of the size distribution of the stratospheric ice clouds are similar to those observed in the upper troposphere. In the tropical troposphere the effective radius of the ice cloud particles decreases from 100 μm at about 10 km altitude, to 3 μm at the tropopause, while the ice water content decreases from 0.04 to 10−5 g m−3. No clear trend in the number concentration was observed with altitude, due to the thin and inhomogeneous characteristics of the observed cirrus clouds. The ice water content calculated from the observed ice crystal size distribution is compared to the ice water content derived from two hygrometer instruments. This independent measurement of the ice water content agrees within the combined uncertainty of the instruments for ice water contents exceeding 2×10−4 g m−3. Stratospheric residence times, calculated based on gravitational settling only, show that the ice crystals observed in the stratosphere over the Hector storm system have a high potential for humidifying the stratosphere. Utilizing total aerosol number concentration measurements from a four channel condensation particle counter, it can be shown that the fraction of activated ice particles with respect to the number of available aerosol particles ranges from 1:300 to 1:30 000 for tropical upper tropospheric ice clouds with ambient temperatures below −75°C.

scholarly journals Evidence for ice particles in the tropical stratosphere from in-situ measurements

2009 ◽  
Vol 9 (18) ◽  
pp. 6775-6792 ◽  
Author(s):  
M. de Reus ◽  
S. Borrmann ◽  
A. Bansemer ◽  
A. J. Heymsfield ◽  
R. Weigel ◽  
...  
Keyword(s):  
Water Content ◽  
Size Distribution ◽  
Crystal Size ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Ice Water Content ◽  
Tropical Troposphere ◽  
Ice Crystal Size ◽  
Ice Water

Abstract. In-situ ice crystal size distribution measurements are presented within the tropical troposphere and lower stratosphere. The measurements were performed using a combination of a Forward Scattering Spectrometer Probe (FSSP-100) and a Cloud Imaging Probe (CIP), which were installed on the Russian high altitude research aircraft M55 "Geophysica" during the SCOUT-O3 campaign in Darwin, Australia. One of the objectives of the campaign was to characterise the Hector convective system, which appears on an almost daily basis during the pre-monsoon season over the Tiwi Islands, north of Darwin. In total 90 encounters with ice clouds, between 10 and 19 km altitude were selected from the dataset and were analysed. Six of these encounters were observed in the lower stratosphere, up to 1.4 km above the local tropopause. Concurrent lidar measurements on board "Geophysica" indicate that these ice clouds were a result of overshooting convection. Large ice crystals, with a maximum dimension up to 400 μm, were observed in the stratosphere. The stratospheric ice clouds included an ice water content ranging from 7.7×10−5 to 8.5×10−4 g m−3 and were observed at ambient relative humidities (with respect to ice) between 75 and 157%. Three modal lognormal size distributions were fitted to the average size distributions for different potential temperature intervals, showing that the shape of the size distribution of the stratospheric ice clouds are similar to those observed in the upper troposphere. In the tropical troposphere the effective radius of the ice cloud particles decreases from 100 μm at about 10 km altitude, to 3 μm at the tropopause, while the ice water content decreases from 0.04 to 10−5 g m−3. No clear trend in the number concentration was observed with altitude, due to the thin and inhomogeneous characteristics of the observed cirrus clouds. The ice water content calculated from the observed ice crystal size distribution is compared to the ice water content derived from two hygrometer instruments. This independent measurement of the ice water content agrees within the combined uncertainty of the instruments for ice water contents exceeding 3×10−4g m−3. Stratospheric residence times, calculated based on gravitational settling, and evaporation rates show that the ice crystals observed in the stratosphere over the Hector storm system had a high potential of humidifying the stratosphere locally. Utilizing total aerosol number concentration measurements from a four channel condensation particle counter during two separate campaigns, it can be shown that the fraction of ice particles to the number of aerosol particles remaining ranges from 1:300 to 1:30 000 for tropical upper tropospheric ice clouds with ambient temperatures below −75°C.

scholarly journals Variability of Microphysical Parameters in High-Altitude Ice Clouds: Results of the Remote Sensing Method

1997 ◽  
Vol 36 (6) ◽  
pp. 633-648 ◽  
Author(s):  
Sergey Y. Matrosov
Keyword(s):  
Remote Sensing ◽  
Water Content ◽  
Cloud Microphysics ◽  
Cloud Base ◽  
Particle Sizes ◽  
Ice Clouds ◽  
Cloud Parameters ◽  
Microphysical Parameters ◽  
Ice Water Content ◽  
Ice Water

Abstract The remote sensing method for retrieving vertical profiles of microphysical parameters in ice clouds from ground-based measurements taken by the Doppler radar and IR radiometer was applied to several cloud cases observed during different field experiments including FIRE-II, ASTEX, and the Arizona Program. The measurements were performed with the NOAA Environmental Technology Laboratory instrumentation. The observed ice clouds were mostly cirrus clouds located in the upper troposphere above 5.6 km. Their geometrical thicknesses varied from a few hundred meters to 3 km. Characteristic cloud particle sizes expressed in median mass diameters of equal-volume spheres varied from about 25 μm to more than 400 μm. Typically, characteristic particle sizes were increasing toward the cloud base, with the exception of the lowest range gates where particles were quickly sublimating. Highest particle concentrations were usually observed near the cloud tops. The vertical variability of particle sizes inside an individual cloud could reach one order of magnitude. The standard deviation of the mean profile for a typical cloud is usually factor of 2 or 3 smaller than mean values of particle characteristic size. Typical values of retrieved cloud ice water content varied from 1 to 100 mg m−3; however, individual variations were as high as four orders of magnitude. There was no consistent pattern in the vertical distribution of ice water content except for the rapid decrease in the vicinity of the cloud base. The relationships between retrieved cloud parameters and measured radar reflectivities were considered. The uncertainty of estimating cloud parameters from the power-law regressions is discussed. The parameters of these regressions varied from cloud to cloud and were comparable to the parameters in corresponding regressions obtained from direct particle sampling in other experiments. Relationships between cloud microphysical parameters and reflectivity can vary even for the same observational case. The variability diminishes if stronger reflectivities are considered. A procedure of “tuning” cloud microphysics–reflectivity regressions for individual profiles is suggested. Such a procedure can simplify the radar–radiometer method and make it applicable for a broader range of clouds.

scholarly journals Evolution of DARDAR-CLOUD ice cloud cloud retrieval: new parameters and impacts on the retrieved microphysical properties

2018 ◽  
Author(s):  
Quitterie Cazenave ◽  
Marie Ceccaldi ◽  
Julien Delanoë ◽  
Jacques Pelon ◽  
Silke Groß ◽  
...  
Keyword(s):  
Water Content ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Microphysical Properties ◽  
Lidar Measurements ◽  
Ice Water Content ◽  
Microphysical Processes ◽  
Pm 10 ◽  
Cloud Ice ◽  
Ice Water

Abstract. In this paper we present the latest refinements brought to the DARDAR-CLOUD product, which contains ice cloud microphysical properties retrieved from the cloud radar and lidar measurements from the A-Train mission. Based on a large dataset of in-situ ice cloud measurements collected during several campaigns performed between 2000 and 2007 in different regions of the globe, the parameterizations used in the microphysical model of the algorithm were assessed and refined to 5 better fit the measurements, keeping the same formalism as proposed in DARDAR basis papers. It is shown that these changes can affect the ice water content retrievals by up to 50 %, with, globally, a reduction of the ice water content and ice water path. In parallel, the retrieved effective radii increase between 5 % and 40 %. The largest differences are found for the warmest temperatures (between −20 °C and 0 °C) in regions where the cloud microphysical processes are more complex and where the retrieval is almost exclusively based on radar-only measurements. In regions where lidar measurements are available, the lidar 10 ratio retrieved for ice clouds is shown to be well constrained by lidar-radar combination or molecular signal detected below thin semi-transparent cirrus. Using this information, the parameterization of the lidar ratio was refined and the new retrieval equals on average 35 sr ± 10 sr in the temperature range between −60 °C and −20 °C.

scholarly journals Dust aerosol impact on North Africa climate: a GCM investigation of aerosol-cloud-radiation interactions using A-Train satellite data

2011 ◽  
Vol 11 (11) ◽  
pp. 31401-31432
Author(s):  
Y. Gu ◽  
K. N. Liou ◽  
J. H. Jiang ◽  
H. Su ◽  
X. Liu
Keyword(s):  
Direct Effect ◽  
North Africa ◽  
Indirect Effect ◽  
Ice Crystal ◽  
Ir Radiation ◽  
Ice Clouds ◽  
Cloud Forcing ◽  
Dust Aerosols ◽  
Ice Water Content ◽  
Ice Water

Abstract. The climatic effects of dust aerosols in North Africa have been investigated using the atmospheric general circulation model (AGCM) developed at the University of California, Los Angeles (UCLA). The model includes an efficient and physically based radiation parameterization scheme developed specifically for application to clouds and aerosols. Parameterization of the effective ice particle size in association with the aerosol first indirect effect based on ice cloud and aerosol data retrieved from A-Train satellite observations have been employed in climate model simulations. Offline simulations reveal that the direct solar, IR, and net forcings by dust aerosols at the top of the atmosphere (TOA) generally increase with increasing aerosol optical depth (AOD). When the dust semi-direct effect is included with the presence of ice clouds, positive IR radiative forcing is enhanced since ice clouds trap substantial IR radiation, while the positive solar forcing with dust aerosols alone has been changed to negative values due to the strong reflection of solar radiation by clouds, indicating that cloud forcing associated with aerosol semi-direct effect could exceed direct aerosol forcing. With the aerosol first indirect effect, the net cloud forcing is generally reduced for an ice water path (IWP) larger than 20 g m−2. The magnitude of the reduction increases with IWP. AGCM simulations show that the reduced ice crystal mean effective size due to the aerosol first indirect effect results in less OLR and net solar flux at the top of the atmosphere over the cloudy area of the North Africa region because ice clouds with smaller size trap more IR radiation and reflect more solar radiation. The precipitation in the same area, however, increases due to the aerosol indirect effect on ice clouds, corresponding to the enhanced convection as indicated by reduced OLR. The increased precipitation appears to be associated with enhanced ice water content in this region. The 200 mb radiative heating rate shows more cooling with the aerosol first indirect effect since greater cooling is produced at the cloud top with smaller ice crystal size. The 500 mb omega indicates stronger upward motion, which, together with the increased cooling effect, results in the increased ice water content. Adding the aerosol direct effect into the model simulation reduces the precipitation in the normal rainfall band over North Africa, where precipitation is shifted to the south and the northeast produced by the absorption of sunlight and the subsequent heating of the air column by dust particles. As a result, rainfall is drawn further inland to the northeast. This study represents the first attempt to quantify the climate impact of the aerosol indirect effect using a GCM in connection with A-train satellite data. The parameterization for the aerosol first indirect effect developed in this study can be readily employed for application to other GCMs.

Snow Size Distribution Parameterization for Midlatitude and Tropical Ice Clouds

2007 ◽  
Vol 64 (12) ◽  
pp. 4346-4365 ◽  
Author(s):  
Paul R. Field ◽  
Andrew J. Heymsfield ◽  
Aaron Bansemer
Keyword(s):  
Water Content ◽  
Size Distribution ◽  
Tropical Rainfall Measuring Mission ◽  
Time Averaging ◽  
Size Distributions ◽  
Regional Study ◽  
Ice Clouds ◽  
Microphysical Process ◽  
Ice Water Content ◽  
Ice Water

Abstract Many microphysical process rates involving snow are proportional to moments of the snow particle size distribution (PSD), and in this study a moment estimation parameterization applicable to both midlatitude and tropical ice clouds is proposed. To this end aircraft snow PSD data were analyzed from tropical anvils [Tropical Rainfall Measuring Mission/Kwajelein Experiment (TRMM/KWAJEX), Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE)] and midlatitude stratiform cloud [First International Satellite Cloud Climatology Project Research Experiment (FIRE), Atmospheric Radiation Measurement Program (ARM)]. For half of the dataset, moments of the PSDs are computed and a parameterization is generated for estimating other PSD moments when the second moment (proportional to the ice water content when particle mass is proportional to size squared) and temperature are known. Subsequently the parameterization was tested with the other half of the dataset to facilitate an independent comparison. The parameterization for estimating moments can be applied to midlatitude or tropical clouds without requiring prior knowledge of the regime of interest. Rescaling of the tropical and midlatitude size distributions is presented along with fits to allow the user to recreate realistic PSDs given estimates of ice water content and temperature. The effects of using different time averaging were investigated and were found not to be adverse. Finally, the merits of a single-moment snow microphysics versus multimoment representations are discussed, and speculation on the physical differences between the rescaled size distributions from the Tropics and midlatitudes is presented.

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