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  • Author or Editor: Ida M. Hakkarinen x
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Robert F. Adler and Ida M. Hakkarinen

Abstract

Aircraft passive microwave observations at 18, 37, 92, and 183 GHz of light oceanic precipitation are studied in conjunction with visible and infrared observations and ground-based radar data. Microwave signatures for clear, cloudy, and precipitating conditions are defined, with results in general agreement with previous theoretical results. Emission signatures are evident at 18, 37, and 92 GHz with clouds and precipitation producing an increase in brightness temperature (T b) over that observed over the low-emissivity ocean background. Polarization differences at 18 and 37 GHz also decrease in precipitation areas to minima of 30 K at 18 GHZ and 15 K at 37 GHz. The 92-GHz T b shows a double-valued relationship, with an increase in cloudy and very lightly raining areas and a subsequent decrease for higher rain rates and deeper clouds where the ice scattering process becomes important. The 183-GHz observations display a distinct sensitivity to small amounts of ice.

Simple channel differences are shown to compare favorably to the rain field, including polarization differences at 18 and 37 GHz and frequency differences between 92 and 37 GHz and between 183 and 92 GHz.

The cases examined include both stratiform and convective structures, and the results indicate that this difference may be important in microwave T b-rain rate relationships. Some of the observed differences may be due to the presence or absence of a melting layer, observed as a radar “bright band.”

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Robert F. Adler, Robert A. Mack, N. Prasad, Ida M. Hakkarinen, and H-Y. M. Yeh

Abstract

Aircraft passive microwave observations of deep atmospheric convection at frequencies between 18 and 183 GHz are presented in conjunction with visible and infrared satellite and aircraft observations and ground-based radar observations. Deep convective cores are indicated in the microwave data by negative brightness temperature (TB) deviations from the land background (270 K) to extreme TB values below 100 K at 37, 92, and 183 GHz and below 200 K at 18 GHz. These TB minima, due to scattering by ice held aloft by the intense updrafts, are well correlated with areas of high radar reflectivity. For this land background case, TB is inversely correlated with rain rate at all frequencies due to TB-ice-rain correlations. Mean ΔT between vertically polarized and horizontally polarized radiance in precipitation areas is approximately 6 K at both 18 GHz and 37 GHz, indicating nonspherical precipitation size ice particles with a preferred horizontal orientation. Convective cores not observed in the visible and infrared data are clearly defined in the microwave observations and borders of convective rain areas are well defined using the high-frequency (90 GHz and greater) microwave observations.

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Christian Kummerow, Ida M. Hakkarinen, Harold F. Pierce, and James A. Weinman

Abstract

This study presents the first quantitative retrievals of vertical profiles of precipitation derived from multispectral passive microwave radiometry. Measurements of microwave brightness temperature (Tb) obtained by a NASA high-altitude research aircraft are related to profiles of rainfall rate through a multichannel piecewise-linear statistical regression procedure. Statistics for Tb are obtained from a set of cloud radiative models representing a wide variety of convective, stratiform, and anvil structures. The retrieval scheme itself determines which cloud model best fits the observed meteorological conditions. Retrieved rainfall rate profiles are converted to equivalent radar reflectivity for comparison with observed reflectivities from a ground-based research radar. Results for two cases studies a stratiform rain situation and an intense convective thunderstorm, show that the radiometrically derived profiles capture the major features of the observed vertical structure of hydrometeor density.

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