Abstract—Falling snow is an important component of global precipitation in extratropical regions. This paper describes the methodology and results of physically based retrievals of snow falling over land surfaces. Because microwave brightness tem-peratures emitted by snow-covered surfaces are highly variable, precipitating snow above such surfaces is difficult to observe using window channels that occur at low frequencies ( 100 GHz). Furthermore, at frequencies 37 GHz, sensitivity to liquid hydrometeors is dominant. These problems are mitigated at high frequencies ( 100 GHz) where water vapor screens the surface emission, and sensitivity to frozen hydrometeors is signifi-cant. However, the scattering effect of snowfall in the atmosphere at those higher frequencies is also impacted by water vapor in the upper atmosphere. The theory of scattering by randomly oriented dry snow particles at high microwave frequencies appears to be better described by regarding snow as a concatenation of “equivalent ” ice spheres rather than as a sphere with the effective dielectric constant of an air–ice mixture. An equivalent sphere snow scattering model was validated against high-frequency attenuation measurements. Satellite-based high-frequency obser-vations from an Advanced Microwave Sounding Unit (AMSU-B) instrument during the March 5–6, 2001 New England blizzard were used to retrieve snowfall over land. Vertical distributions of snow, temperature, and relative humidity profiles were derived from the Mesoscale Model (MM5) cloud model. Those data were applied and modified in a radiative transfer model that derived brightness temperatures consistent with the AMSU-B observa-tions. The retrieved snowfall distribution was validated with radar reflectivity measurements obtained from a ground-based radar network. Index Terms—Electromagnetic scattering, estimation, mil-limeter-wave radiometry, remote sensing, satellite, snow. I.

This paper presents a new, purely physical approach to simulate ice-particle scattering at microwave frequencies. Temperature-dependent ice particle size distributions measured by aircraft in midlatitude frontal systems are used to represent the distribution of precipitation-sized frozen hydrometeors above the freezing level through derived radar reflectivity–snow water content (Z–M) relationships. The discrete dipole approximation is employed to calculate optical properties of selected types of idealized nonspherical ice particles (hexagonal columns, four-arm rosettes, and six-arm rosettes). Based on those assumptions, passive microwave optical properties are calculated using radar observations from Gotland Island in the Baltic Sea. These forward-simulated brightness temperatures are compared with observed data from both the Advanced Microwave Scanning Radiometer (AMSR-E) and the Advanced Microwave Sounding Unit-B (AMSU-B). Results show that the new ice scattering/microphysics model is able to generate bright-ness temperatures that are consistent with AMSR and AMSU-B observations of two light-winter-precipitation cases. The overall differences among the various ice-habit results at 89 GHz are generally not that expansive, whereas the AMSU-B 150-GHz comparisons show increased sensitivity to ice-particle shapes. 1.

[1] The single-scattering properties of ice crystals are fundamental to the radiative transfer in ice clouds, which thereby are the basis for estimating the optical and microphysical properties of ice clouds. This study computes the scattering and absorption properties of nonspherical ice crystals in ice clouds using the discrete dipole approximation method at frequencies of 89–340 GHz. Six ice crystal habits, including hexagonal column, hollow column, six-branch bullet rosette, droxtal, aggregate, and plate, ranging in maximum dimensions from 2 to 5500 mm, are considered. The single-scattering properties of ice crystals are sensitive to their habits. The sensitivity of the angular distribution of the scattering energy to ice crystal habits is also evident and increases with size of ice crystal. The mean scattering properties of ice clouds with two ice crystal habit distributions are computed by averaging the single-scattering properties over a Gamma particle size distribution. It is found that the mean scattering properties of ice clouds are strongly dependent on ice cloud effective particle size and microwave frequency. The mean scattering properties increase with increasing ice cloud effective particle size and microwave frequency. On the basis of the calculated mean optical properties, parameterizations of the mean scattering efficiency, absorption efficiency, and asymmetry factor as functions of ice cloud effective particle size are developed. Citation: Hong, G. (2007), Parameterization of scattering and absorption properties of nonspherical ice crystals at microwave frequencies, J. Geophys. Res., 112, D11208, doi:10.1029/2006JD008364. 1.

[1] The sensitivity of microwave brightness temperatures at the frequencies between 89 and 190 GHz to surface emissivities and hydrometeors in a tropical deep convective cloud system is investigated by simulations, using the Goddard Cumulus Ensemble model data of a simulated oceanic tropical squall line as input for a radiative transfer model. It is found that only the window channel at 89 GHz has an apparent dependence on the surface emissivity. The three water vapor channels around 183 GHz (i.e., 183.3 ± 1, ±3, and ±7 GHz) are completely independent, and the window channel at 150 GHz is nearly independent of the surface emissivity because of the atmospheric opacity at these frequencies. All channels are apparently influenced by deep convective clouds and their outflowing thick cirrus clouds. The channels at 89, 150, and 183.3 ± 7 GHz are strongly sensitive to variations in the liquid water content at levels above 5 km. The sensitivity of the channel at 150 GHz to liquid water is about twice that at 183.3 ± 7 GHz. All channels are generally sensitive to variations in the frozen hydrometeor content at levels above 7 km. The 183.3 ± 1 GHz channel has virtually no influence from the frozen hydrometeors at levels below 7 km. The sensitivity suggests that it should be possible to estimate the frozen hydrometeor properties in levels above 7 km in tropical deep convective clouds using the water vapor channels around 183 GHz.

The Global Precipitation Mission (GPM) is a joint mission between the National Aeronautics and Space Agency (NASA) and the Japanese Aerospace Exploration Agency (JAXA). It builds upon the heritage of the Tropical Rainfall Measuring Mission (TRMM) with an advanced core spacecraft augmented by a constellation satellite and other satellites of opportunity (i.e, other international satellite systems with precipitation-sensing instrument payloads). With changes to satellite missions and sensor capabilities, it is unlikely that the GPM constellation configuration will be known until close to deployment, and will change during the lifetime of GPM. It is instructive to note how the retention or loss of a particular satellite platform and/or sensor type will affect the performance of the GPM precipitation products and other applications that utilize GPM products. In this study, we use the existing (2008) constellation of various active radar and passive microwave-based platforms to examine the impact of several proxy GPM satellite constellation configurations. The emphasis is on how high resolution precipitation products (HRPP) are affected by such factors as sensor type (conical or across-track scanning) and nodal crossing time, using a collection of GPM proxy datasets gathered over the continental United States. The validation is presented two ways. The first is by traditional validation using an existing surface gauge network analysis (Chen et. al, 2008). The second is more indirect, through examination of how the soil moisture state of the Noah land surface model (LSM) is impacted when the LSM is forced with the various precipitation datasets, each corresponding to a different proxy GPM constellation configuration.

Clouds exert a profound influence on both the water balance of the atmosphere and the earth’s radiation budget (Stephens 2005; Stephens and Kummerow 2007). Among the global distribution, 30 % of them are ice clouds (Riedi et al. 2000). It is important to improve our knowledge of the ice cloud properties in order to determine their influence to the global ecosystem. For ice clouds with millimeter-size ice particles, which are generally found in anvil cirrus and deep convections, microwave and millimeter wave length satellite measurements are suitable for the ice cloud microphysical property retrieval because of its strong ability to penetrate deeper into dense ice clouds. For these types of ice clouds, brightness temperatures at the top of the atmosphere are analytically derived as a function of vertically integrated ice water content (i.e. ice water path), effective particle diameter, and bulk volume density. In general, three brightness temperature measurements are needed to retrieve the three ice cloud microphysical parameters. A two-stream radiative transfer theory was applied to data from the Advanced Microwave Sounding Unit (AMSU) and the Moisture Humidity Sensor (MHS) in order to generate global ice water paths

doi:10.5194/amt-8-1055-2015 © Author(s) 2015. CC Attribution 3.0 License. A layer-averaged relative humidity profile retrieval for microwave observations: design and results for the Megha-Tropiques payload

In order to better understand the characteristics of frozen cloud particles in hurricane systems, computed brightness temperatures were compared with radiometric observations of Hurricane Erin (2001) from the NASA ER-2 aircraft. The focus was oil the frozen particle microphysics and the high frequencies (2 85 GHz) that are particularly sensitive to frozen particles. Frozen particles in hurricanes are an indicator of increasing hurricane intensity. In fact "hot towers " associated with increasing hurricane intensity are composed of frozen ice cloud particles. (They are called hot towers because their column of air is warmer than the surrounding air temperature, but above about 5-7 krn to the tops of the towers at 15- 19 krn, the cloud particles are frozen.) This work showed that indeed, one can model information about cloud ice particle characteristics and indicated that mon-spherical ice shapes, instead of spherical particles, provided the best match to the observations. Overall, this work shows that while non-spherical particles show promise, selecting and modeling a proper ice particle parameterization can be difficult and additional in situ measurements are needed to define and validate appropriate parameterizations. This work is important for developing Global Precipitation

[1] In order to better understand the characteristics and physical-to-radiative relationships of frozen hydrometeors in hurricane systems, computed brightness temperatures (TB) from 10.7 to 183 ± 10 GHz were compared with radiometric observations of Hurricane Erin (2001) from the NASA ER-2 aircraft. The focus was on the high frequencies (85 GHz) that are particularly sensitive to frozen hydrometeors. In order to initialize the cloud profiles used in the radiative transfer calculations, data from airborne radars, dropsondes, and cloud models were used. Three different ice habit and size parameterizations were used with these cloud profiles to obtain the particle radiative signatures including (1) spherical particles with size distributions derived from in situ observations, (2) spherical ‘‘fluffy’ ’ snow and graupel particles with modified Marshall-Palmer size distributions, and (3) a non-spherical bullet rosette habit where the radiation attributes (scattering, absorption, and asymmetry properties) were computed using the Discrete Dipole Approximation. In addition, three different reflectivity to ice water content (Z-IWC) relationships were used with the three habit and size parameterizations to provide a measure of the sensitivity of the Z-IWC relationship. This work showed that both the

The potential of the Advanced Microwave Sounding Unit (AMSU) observations for the depiction and tracking of intense high-latitude mesoscale maritime weather systems, called polar lows, is explored. Since a variety of mechanisms are important for their development and maintenance, this investigation is based on three polar low cases of different types. The AMSU-B channels at 183 GHz are able to locate convective polar lows (PL) even in their incipient stage, at a time when there is considerable uncertainty as to the nature of the cloud structures seen in the visible or infrared imagery. This detection is based on temperature depression due to scattering by hydrometeors, as confirmed by comparison with radar data. These same channels will, however, fail to unambiguously detect weakly convective and mainly baroclinic PL. The AMSU-A channels help documenting the large-scale environment in which PL develop. Channel 5 clearly shows the cold air outbreaks associated with these developments, whereas the difference between channels 7 and 5 can be used to detect and locate positive upper-level potential vorticity anomalies. Because of the high temporal availability of AMSU observations and despite some limitations pointed out in this study, these results are relevant for PL forecasting and monitoring. 1.