A Microphysics-Scheme-Consistent Snow Optical Parameterization for the Community Radiative Transfer Model

Abstract

The satellite observational data assimilation community requires consistent hydrometer descriptions—including mass-size relation and particle size distribution—to be used in both the forecast model and observation operator. We develop a microphysics scheme-consistent snow and graupel single-scattering property database to meet this requirement. In this database, snowflakes are modeled as a mixture of small column and large aggregated ice particles, the mixing ratios of which may be adjusted to satisfy a given mass-size relation. Snow single-scattering properties are computed for four different mass-size relations. Subsequently, the snow description in the Thompson microphysics scheme is used as an example to demonstrate how microphysics scheme-consistent snow bulk optical properties are derived. The Thompson scheme-consistent snow bulk optical properties are added to the Community Radiative Transfer Model (CRTM) version 2.4.0. With CloudSat Cloud Profiling Radar (CPR) snow and liquid precipitation retrievals as the inputs, CRTM simulations are performed over global oceans and compared with four collocated Global Precipitation Measurement (GPM) Microwave Imager (GMI) high-frequency channel observations. The CRTM simulated brightness temperatures show agreement with the GMI observed brightness temperatures in cases of light-to-moderate precipitation over extratropical and polar ice-free oceans, with root mean square errors (RMSEs) of 4.3, 13.0, 1.8, and 3.3 K in the 166 GHz (vertical polarization), 166 GHz (horizontal polarization), 183±3 GHz (vertical polarization), and 183±7 GHz (vertical polarization) channels, respectively. The result demonstrates the potential of using the newly developed microphysics scheme-consistent snow optical parameterization in data assimilation applications.

Improved Temperature‐Dependent Ice Refractive Index Compilation in the Far‐Infrared Spectrum

“…The second sensitivity study described in Section 2 compares the bulk optical properties computed using the IY11 and the new ice refractive index compilation at 3 wavelengths, where the largest differences in the real or imaginary refractive index components are found, to illustrate possible effects of the new refractive index 1can be used to calculate β ext,m , ω, and g as in previous studies (e.g., Baum et al, 2005;Ren et al, 2023). In this study, we calculate β ext,m , ω, and g for 51 r eff values from 5 to 130 μm with an increment of 2.5 μm.…”

“…For given r eff values of interest, associated Λ values satisfying Equations and can be found. With the Λ values, N ( D max ) in Equation can be used to calculate β ext,m , ω, and g as in previous studies (e.g., Baum et al., 2005; Ren et al., 2023). In this study, we calculate β ext,m , ω, and g for 51 r eff values from 5 to 130 μm with an increment of 2.5 μm.…”

“…Using the compilation involved in WB08 and six other data sets (Table S1 in Supporting Information ), Iwabuchi and Yang (2011) (hereinafter referred to as IY11) developed a temperature‐dependent data set of ice refractive index, which also spans 0.0443–10 6 μm at 12 temperatures from 160 to 270 K in 10 K increments. This data set has been used to model frozen hydrometeor optical properties in the microwave (MW) region (Ding et al., 2017; Ren et al., 2023), where the temperature‐dependence of ice optical constants is most significant. However, IY11 indicated that more reliable measurements were needed in the spectral region between 70 and 300 μm.…”