scholarly journals On cloud ice induced absorption and polarisation effects in microwave limb sounding

2011 ◽  
Vol 4 (2) ◽  
pp. 1493-1531
Author(s):  
P. Eriksson ◽  
B. Rydberg
Keyword(s):  
Significant Degree ◽  
Single Scattering ◽  
Particle Sizes ◽  
Ice Clouds ◽  
Oblate Spheroids ◽  
Orthogonal Components ◽  
Ice Water Content ◽  
Combine Information ◽  
Cloud Ice ◽  
Ice Water

Abstract. Detailed simulations of microwave limb sounding in the presence of ice clouds have been performed. It is clarified that, while particle absorption normally gives no significant change of the measured radiance for down-looking measurements, this is not the case for limb sounding. The particles were treated as horizontally aligned oblate spheroids and for this assumption on particle shape, and comparable situations, no significant degree of circular polarisation is generated. Differences between the brightness temperature of the ±45° polarisation components up to 4 K were found, but this difference appears to be small as long as single scattering conditions apply. The cloud extinction is the smallest for the vertically polarised component, but it should be more beneficial to observe any of the ±45° and circularly polarised components if ice water content is also a target of the retrievals. These latter pairs of orthogonal components also make it easier to combine information measured from different positions and with different polarisations. The results indicate that single scattering can be assumed for cloud optical thicknesses below about 0.1, which is thus an important threshold with respect to the complexity and accuracy of retrievals. The representation of particle sizes during the retrieval is discussed.

scholarly journals On cloud ice induced absorption and polarisation effects in microwave limb sounding

2011 ◽  
Vol 4 (6) ◽  
pp. 1305-1318 ◽  
Author(s):  
P. Eriksson ◽  
B. Rydberg ◽  
S. A. Buehler
Keyword(s):  
Water Content ◽  
Significant Degree ◽  
Single Scattering ◽  
Three Dimensions ◽  
Mixing Ratios ◽  
General Finding ◽  
Oblate Spheroids ◽  
Orthogonal Components ◽  
Ice Water Content ◽  
Ice Water

Abstract. Microwave limb sounding in the presence of ice clouds was studied by detailed simulations, where clouds and other atmospheric variables varied in three dimensions and the full polarisation state was considered. Scattering particles were assumed to be horizontally aligned oblate spheroids with a size distribution parameterized in terms of temperature and ice water content. A general finding was that particle absorption is significant for limb sounding, which is in contrast to the down-looking case, where it is usually insignificant. Another general finding was that single scattering can be assumed for cloud optical paths below about 0.1, which is thus an important threshold with respect to the complexity and accuracy of retrieval algorithms. The representation of particle sizes during the retrieval is also discussed. Concerning polarisation, specific findings were as follows: Firstly, no significant degree of circular polarisation was found for the considered particle type. Secondly, for the ±45° polarisation components, differences of up to 4 K in brightness temperature were found, but differences were much smaller when single scattering conditions applied. Thirdly, the vertically polarised component has the smallest cloud extinction. An important goal of the study was to derive recommendations for future limb sounding instruments, particularly concerning their polarisation setup. If ice water content is among the retrieval targets (and not just trace gas mixing ratios), then the simulations show that it should be best to observe any of the ±45° and circularly polarised components. These pairs of orthogonal components also make it easier to combine information measured from different positions and with different polarisations.

scholarly journals UARS/MLS Cloud Ice Measurements: Implications for H2O Transport near the Tropopause

2005 ◽  
Vol 62 (2) ◽  
pp. 518-530 ◽  
Author(s):  
D. L. Wu ◽  
W. G. Read ◽  
A. E. Dessler ◽  
S. C. Sherwood ◽  
J. H. Jiang
Keyword(s):  
Water Content ◽  
Total Water ◽  
Ice Clouds ◽  
Clear Sky ◽  
Ice Water Content ◽  
Satellite Microwave ◽  
Cold Point ◽  
Cloud Ice ◽  
Ice Water

Abstract A technique for detecting large hydrometeors at high altitudes is described here and applied to the Upper Atmosphere Research Satellite/Microwave Limb Sounder (UARS/MLS) 203-GHz radiance measurements at tangent pressures between 200 and 46 hPa. At these tangent pressures the radiances remain optically thin and cloudy-sky radiances are brighter than normal clear-sky cases. Unlike infrared/visible cloud observations, the 203-GHz radiances can penetrate most ice clouds and are sensitive to ice crystals of convective origin. Rough ice water content (IWC) retrievals are made near the tropopause using estimated size distributions from in situ convective studies. The seasonal mean IWC observed at 100 hPa reaches vapor-equivalent 20 ppmv or more over convective centers, dominating the total water content. Convectively lofted ice, therefore, appears to be hydrologically significant at the tropical cold point. IWC is well correlated spatially with relative humidity with respect to ice (RHi) at 100 hPa during both the dry (January–March) and moist (July–September) periods.

scholarly journals 3-D polarised simulations of space-borne passive mm/sub-mm midlatitude cirrus observations: a case study

2006 ◽  
Vol 6 (6) ◽  
pp. 12701-12728 ◽  
Author(s):  
C. P. Davis ◽  
K. F. Evans ◽  
S. A. Buehler ◽  
D. L. Wu ◽  
H. C. Pumphrey
Keyword(s):  
Water Cycle ◽  
Spherical Geometry ◽  
Radar Data ◽  
Radiation Balance ◽  
Ice Clouds ◽  
Ice Water Content ◽  
Actual Field ◽  
Remote Sensing Techniques ◽  
Cloud Ice ◽  
Ice Water

Abstract. Global observations of ice clouds are needed to improve our understanding of their impact on earth's radiation balance and the water-cycle. Passive mm/sub-mm has some advantages compared to other space-borne cloud-ice remote sensing techniques. This paper presents detailed simulated observations for three such instruments, AMSU-B, CIWSIR, and EOS-MLS. The Monte-Carlo radiative transfer code, ARTS-MC, makes proper account of polarisation and uses 3-D spherical geometry. The actual field of view characteristics for each instrument are also accounted for. A 3-D midlatitude cirrus scenario is used, which is derived from Chilbolton cloud radar data and a stochastic method for generating 3-D ice water content fields. Although the main purpose of the work was to demonstrate the capability of accurately simulating observations of this type, the results suggest that cloud inhomogeneity will affect CIWSIR, and EOSMLS low tangent height observations via the beamfilling effect. Also, the results confirm that preferentially oriented ice crystals will produce significant polarisation effects.

scholarly journals Toward Understanding the Properties of High Ice Clouds at the Naqu Site on the Tibetan Plateau Using Ground-Based Active Remote Sensing Measurements Obtained during a Short Period in July 2014

2016 ◽  
Vol 55 (11) ◽  
pp. 2493-2507 ◽  
Author(s):  
Chuanfeng Zhao ◽  
Liping Liu ◽  
Qianqian Wang ◽  
Yanmei Qiu ◽  
Wei Wang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
The Tibetan Plateau ◽  
Regression Equations ◽  
Ice Clouds ◽  
Cloud Radar ◽  
Microphysical Properties ◽  
Short Period ◽  
Ice Water Content ◽  
Cloud Ice ◽  
Ice Water

AbstractThis study describes the microphysical properties of high ice clouds (with bases above 5 km) using ground-based millimeter cloud radar cirrus-mode observations over the Naqu site of the Tibetan Plateau (TP) during a short period from 6 to 31 July 2014. Empirical regression equations are applied for the cloud retrievals in which the parameters are given on the basis of a review of existing literature. The results show a unimodal distribution for the cloud ice effective radius re and ice water content with maximum frequencies around 36 μm and 0.001 g m−3, respectively. Analysis shows that clouds with high ice re are more likely to occur at times from late afternoon until nighttime. The clouds with large (small) re mainly occur at low (high) heights and are likely orographic cumulus or stratocumulus (thin cirrus). Further analysis indicates that ice re decreases with increasing height and shows strong positive relationships between ice re (μm) and depth h (m), with a regression equation of re = 35.45 + 0.0023h + (1.7 × 10−7)h2. A good relationship between ice re and temperature T (°C) is found, re = 44.65 + 0.1438T, which could serve as a baseline for retrieval of characteristic ice re properties over the TP.

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 A general database of hydrometeor single scattering properties at microwave and sub-millimetre wavelengths

2018 ◽  
Author(s):  
Patrick Eriksson ◽  
Robin Ekelund ◽  
Jana Mendrok ◽  
Manfred Brath ◽  
Oliver Lemke ◽  
...  
Keyword(s):  
Electromagnetic Waves ◽  
Single Scattering ◽  
Particle Orientation ◽  
Maximum Diameter ◽  
Particle Sizes ◽  
Orientation Data ◽  
Different Types ◽  
Rain Drops ◽  
Cloud Ice ◽  
Random Particle

Abstract. A main limitation today in simulations and inversions of microwave observations of ice hydrometeors (cloud ice, snow, hail ...) is the lack of data describing the interaction between electromagnetic waves and the particles. To improve the situation, the development of a comprehensive dataset of such "scattering properties" has been started. The database aims at giving a broad coverage in both frequency (1 to 886 GHz) and temperature (190 to 270 K), to support both passive and active current and planned measurements, and to provide data corresponding to the full Stokes vector. This first version of the database is restricted to totally random particle orientation. Data for 34 particle sets, i.e. habits, have been generated. About 17 of the habits can be classified as single crystals, three habits can be seen as heavily rimed particles, and remaining habits are aggregates of different types, representing e.g. snow and hail. The particle sizes considered vary between the habits, but a maximum diameter of 10 and 20 mm are typical values for the largest single crystal and aggregate particles, respectively, and the number of sizes per habit is at least 30. Particles containing liquid water are also inside the scope of the database, but this phase of water is so far only represented by a liquid sphere habit. The database is built upon the netCDF4 file format. Interfaces to browse, extract and convert data for selected radiative transfer models are provided in Matlab and Python. The database and associated tools are publically available from Zenedo (https://doi.org/10.5281/zenodo.1175572 and https://doi.org/10.5281/zenodo.1175588, respectively). Planned extensions include non-spherical rain drops, melting particles and a second orientation case that can be denoted as azimuthally random.

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.

Sign in / Sign up

Export Citation Format

Share Document