Abstract
Abstract. Large ice hydrometeors are usually present in intense convective clouds and may significantly affect the upwelling radiances that are measured by satellite-borne microwave radiometers – especially, at millimeter-wavelength frequencies. Thus, interpretation of these measurements (e.g., for precipitation retrieval) requires knowledge of the single scattering properties of ice particles. On the other hand, shape and internal structure of these particles (especially, the larger ones) is very complex and variable, and therefore it is necessary to resort to simplifying assumptions in order to compute their single-scattering parameters. In this study, we use the discrete dipole approximation (DDA) to compute the absorption and scattering efficiencies and the asymmetry factor of two kinds of quasi-spherical and non-homogeneous soft-ice particles in the frequency range 50–183 GHz. Particles of the first kind are modeled as quasi-spherical ice particles having randomly distributed spherical air inclusions. Particles of the second kind are modeled as random aggregates of ice spheres having random radii. In both cases, particle densities and dimensions are coherent with the snow hydrometeor category that is utilized by the University of Wisconsin – Non-hydrostatic Modeling System (UW-NMS) cloud-mesoscale model. Then, we compare our single-scattering results for randomly-oriented soft-ice hydrometeors with corresponding ones that make use of: a) effective-medium equivalent spheres, b) solid-ice equivalent spheres, and c) randomly-oriented aggregates of ice cylinders. Finally, we extend to our particles the scattering formulas that have been developed by other authors for randomly-oriented aggregates of ice cylinders.
Highlights
Several currently flown microwave radiometers provide observations in the frequency range 85–190 GHz – e.g., the Special Sensor Microwave Temperature 2 (SSM/T2) and the Special Sensor Microwave Imager Sounder (SSMIS) onboard satellites of the US Defense Meteorological Satellite Program (DMSP), the Advanced Microwave Sounding Unit B (AMSU-B) aboard NOAA-15, 16, 17, 18 operational satellites, the Humidity Sounder for Brazil (HSB) aboard NASA’s Aqua Mission, and the Microwave Humidity Sounder (HMS) onboard EUMETSAT’s MetOp operational satellite
We use the discrete dipole approximation (DDA) method to compute the single-scattering parameters of these particles in the frequency range 50–183 GHz, and compare our results for randomly-oriented particles with corresponding results for the equivalent ice spheres of the Maxwell Garnett and Grenfell and Warren (1999) approximations, as well as with the scattering formulas developed by Weinman and Kim (2007) for randomly-oriented aggregates of ice cylinders
Particle bulk density and dimensions are coherent with the snow hydrometeor category that is utilized by the University of Wisconsin – Non-hydrostatic Modeling System (UW-NMS) cloud-mesoscale model developed by Tripoli (1992), which we use for generating the cloudradiation databases (Tripoli et al, 2007) for our precipitation retrieval algorithm (Sanoet al., 2008) – i.e., snow density is fixed to 0.2 g/cm3 and the radius (r) of the circumscribing sphere varies from 0.013 cm to 0.5 cm
Summary
Several currently flown microwave radiometers provide observations in the frequency range 85–190 GHz – e.g., the Special Sensor Microwave Temperature 2 (SSM/T2) and the Special Sensor Microwave Imager Sounder (SSMIS) onboard satellites of the US Defense Meteorological Satellite Program (DMSP), the Advanced Microwave Sounding Unit B (AMSU-B) aboard NOAA-15, 16, 17, 18 operational satellites, the Humidity Sounder for Brazil (HSB) aboard NASA’s Aqua Mission, and the Microwave Humidity Sounder (HMS) onboard EUMETSAT’s MetOp operational satellite. We use the DDA method to compute the single-scattering parameters of these particles in the frequency range 50–183 GHz, and compare our results for randomly-oriented particles with corresponding results for the equivalent ice spheres of the Maxwell Garnett and Grenfell and Warren (1999) approximations, as well as with the scattering formulas developed by Weinman and Kim (2007) for randomly-oriented aggregates of ice cylinders. We extend these scattering formulas to our quasi-spherical soft-ice particles
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