Microwave radiances from precipitating clouds containing aspherical ice, combined phase, and liquid hydrometeors

Abstract

Microwave radiances have been computed as a function of rainfall rates from precipitating clouds containing ice, combined phase, and water hydrometeors. The ice at the top of the precipitating cloud depresses the brightness temperatures by reflecting radiances that emerge from the liquid hydrometeors at lower altitudes. Because the density of ice hydrometeors is related to the rainfall rate at the surface, the brightness temperatures are sensitive to large rainfall rates. The solution of the transfer equation considers the vertically inhomogeneous structure of the precipitation as well as the polarized emissivity of the underlying surface. The altitudes from which radiances derive their energy are presented for several rainfall profiles and frequencies. It is shown that the lower‐frequency radiances are sensitive to liquid precipitation at low altitudes while the higher‐frequency radiances are more sensitive to the ice hydrometeors at the cloud tops. The extinction coefficients of aspherical hydrometeors are presented as a function of rainfall rates. Measurements at 37.0‐GHz microwave radiances from Nimbus 7 suggest that the vertically polarized radiances are 12±2°K warmer than the horizontally polarized radiances at high rainfall rates. This difference diminishes at lower frequencies. The present model reveals that such effects can be traced to aspherical ice hydrometeors in the upper regions of precipitating clouds.

Precipitation characteristics over land from the NOAA‐15 AMSU sensor

“…The rain retrieval over land is inherently more difficult than over ocean since the suspended liquid associated with clouds/rain and the land surface are both strong emitters (as opposed to a water surface which is a weak emitter). Thus, the land retrieval is based on the scattering signal of millimeter sized ice hydrometeors in precipitating atmospheres [Wu and Weinman, 1984]. This retrieval method becomes more difficult due to the indirect relationship between volume ice scattering and surface rain rate, and the non-uniqueness of the rain signature from other radiometrically similar surfaces (i.e., snow cover and deserts) [Grody, 1991].…”

A TRMM Microwave Radiometer Rain Rate Estimation Method with Convective and Stratiform Discrimination

“…We emphasize the 85 GHz TMI data in this study because, of all the channels of this radiometer, the 85 GHz channel has the finest spatial resolution and the highest extinction to ice and liquid hydrometeors. In particular, the scattering of microwave radiation, which according to radiative transfer theory results in a depression in the 85 GHz data, is strongly related to cloud ice content (Wu and Weinman 1984). The surface rain rate map deduced from the PR data for the same time period (within two minutes) is shown in Fig. lb.…”

Distribution of Convective Intensities in West Africa Using Reflectivity and Ice Scattering Characteristics from TRMM Precipitation Features

“…For many observational purposes, it is appropriate to think of 85-GHz as simply an ice scattering channel (e.g., [5] [14]), in which precipitation sized ice reduces the observed brightness temperature by scattering the upwelling radiation [7] [8] [9] [10].…”

“…This attenuation is related to the surface rain rate via assumptions about the partitioning of cloud and rain water, and the vertical profile of rain water. The scattering signal is observed when the brightness temperature is depressed [7] [8] [9] [10] by scattering due to optical depths of precipitation-sized ice particles above the freezing level within the instrument footprint (5 -7 km for TMI, with 14 km between successive scans), which is also related to clouds and precipitation. The magnitude of this ice scattering signature depends on the optical depth, which in turn depends on factors such as the wavelength, the vertical distribution of hydrometeors, and the phase, density, size, and concentration of these hydrometeors.…”