Comparison of using distribution‐specific versus effective radius methods for hydrometeor single‐scattering properties for all‐sky microwave satellite radiance simulations with different microphysics parameterization schemes

Abstract

The Community Radiative Transfer Model (CRTM) presently uses one look‐up table (LUT) of cloud and precipitation single‐scattering properties at microwave frequencies, with which any particle size distribution may interface via effective radius. This may produce scattering properties insufficiently representative of the model output if the microphysics parameterization scheme particle size distribution mismatches that assumed in constructing the LUT, such as one being exponential and the other monodisperse, or assuming different particle bulk densities. The CRTM also assigns a 5 μm effective radius to all nonprecipitating clouds, an additional inconsistency. Brightness temperatures are calculated from 3 h convection‐permitting simulations of Hurricane Karl (2010) by the Weather Research and Forecasting model; each simulation uses one of three different microphysics schemes. For each microphysics scheme, a consistent cloud scattering LUT is constructed; the use of these LUTs produces differences in brightness temperature fields that would be better for analyzing and constraining microphysics schemes than using the CRTM LUT as‐released. Other LUTs are constructed which contain one of the known microphysics inconsistencies with the CRTM LUT as‐released, such as the bulk density of graupel, but are otherwise microphysics‐consistent; differences in brightness temperature to using an entirely microphysics‐consistent LUT further indicate the significance of that inconsistency. The CRTM LUT as‐released produces higher brightness temperature than using microphysics‐consistent LUTs. None of the LUTs can produce brightness temperatures that can match well to observations at all frequencies, which is likely due in part to the use of spherical particle scattering.

Representing Precipitation Ice Species With Both Spherical and Nonspherical Particles for Radiative Transfer Modeling of Microphysics‐Consistent Cloud Microwave Scattering Properties

“…The WRF model was run to produce high‐resolution forecasts of Hurricane Karl (2010) during rapid intensification in the Bay of Campeche from 22 UTC 16 September to 15 UTC 17 September. Following Sieron et al (), the WRF simulations were initialized with an ensemble Kalman filter analysis assimilating airborne Doppler radar radial velocity observations as presented in Melhauser et al () with the methodologies developed in Zhang and Weng () and Weng and Zhang (). The WSM6 (Dudhia et al, ) microphysics scheme was used; the scheme has liquid cloud, rain, ice cloud, snow, and graupel hydrometeor species.…”

“…The WSM6 (Dudhia et al, ) microphysics scheme was used; the scheme has liquid cloud, rain, ice cloud, snow, and graupel hydrometeor species. Further description of the initial conditions and WRF configurations are provided in Sieron et al ().…”

“…Then brightness temperatures were simulated after replacing the soft sphere scattering properties for either one or two of the precipitation ice species with those from nonspherical particles (as described in the following paragraphs). The 3 km grid spaced simulated brightness temperatures were convolved to the locations observed by the Defense Meteorological Satellite Program (DMSP) F‐16 SSMIS overpass at 0113 UTC 17 September using a simple symmetric Gaussian weighting function (Bennartz, ; see Sieron et al, ). The average effective field of view for SSMIS on a DMSP satellite varies from about 57.7 km at 19.35 GHz to 14.4 km at 183.31 GHz.…”

“…Significant challenges in assimilating precipitation‐affected brightness temperatures have involved the use of a radiative transfer model as the observation operator, particularly the effects of ice scattering (e.g., Kulie et al, ). In Sieron et al (), microwave scattering lookup tables for clouds and precipitation for the Community Radiative Transfer Model (CRTM; Han et al, ) were constructed to ensure that simulations are consistent with the respective particle properties (i.e., homogenous spheres) and size distributions specified by the WRF 6‐Species Single‐Moment (WSM6; Dudhia et al, ), Goddard (Lang et al, ), and Morrison (Morrison et al, ) microphysics schemes in the Weather Research and Forecasting (WRF) model (Skamarock et al, ). For the particle sizes, , of the precipitation species (rain, snow, and graupel, which are responsible for most of the departures from clear‐sky brightness temperatures), all three schemes use a gamma distribution, with and with the shape parameter , otherwise known as an exponential distribution.…”

“…Differences in cloud scattering properties between the new CRTM‐DS and existing CRTM‐RE lookup tables—perhaps due to inconsistencies in the particle size distribution between the microphysics and the CRTM‐RE lookup table—result in much lower simulated brightness temperatures from the former (Sieron et al, ). But both approaches produced inconsistent brightness temperatures across several frequencies as compared with observations.…”