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  • Author or Editor: Kenneth D. Leppert II x
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Kenneth D. Leppert II and Daniel J. Cecil

Abstract

Passive microwave brightness temperatures (BTs) collected above severe thunderstorms using the Advanced Microwave Precipitation Radiometer and Conical Scanning Millimeter-Wave Imaging Radiometer during the Midlatitude Continental Convective Clouds Experiment are compared with a hydrometeor identification applied to dual-polarimetric Weather Surveillance Radar-1988 Doppler radar data collected at Vance Air Force Base, Oklahoma (KVNX). The goal of this work is to determine the signatures of various hydrometeor species in terms of BTs measured at frequencies used by the Global Precipitation Measurement mission Microwave Imager. Results indicate that hail is associated with an ice-scattering signature at all frequencies examined, including 10.7 GHz. However, it appears that frequencies ≤ 37.1 GHz are most useful for identifying hail. Low-level (below 2.5 km) hail becomes probable for a BT below 240 K at 19.4 GHz, 170 K at 37.1 GHz, 90 K at 85.5 GHz, 80 K at 89.0 GHz, 100 K at 165.5 GHz, and 100 K at 183.3 ± 7 GHz. Graupel may be distinguished from hail and profiles without any hydrometeor species by its strong scattering signature at higher frequencies (e.g., 165.5 GHz) and its relative lack of scattering at frequencies ≤ 19.4 GHz. There is a clearer distinction between profiles that contain liquid precipitation and profiles without any hydrometeors when the liquid is associated above with hail and/or graupel (i.e., a hydrometeor category with a strong scattering signature) than when the liquid is associated with smaller ice. Near-surface precipitation is much more likely for a 19.4-GHz BT < 250 K, 37.1-GHz BT < 240 K, 89.0-GHz BT < 220 K, and 165.5-GHz BT < 140 K.

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Kenneth D. Leppert II and Daniel J. Cecil

Abstract

Global Precipitation Measurement (GPM) Microwave Imager (GMI) brightness temperatures (BTs) were simulated over a case of severe convection in Texas using ground-based S-band radar and the Atmospheric Radiative Transfer Simulator. The median particle diameter D o of a normalized gamma distribution was varied for different hydrometeor types under the constraint of fixed radar reflectivity to better understand how simulated GMI BTs respond to changing particle size distribution parameters. In addition, simulations were conducted to assess how low BTs may be expected to reach from realistic (although extreme) particle sizes or concentrations. Results indicate that increasing D o for cloud ice, graupel, and/or hail leads to warmer BTs (i.e., weaker scattering signature) at various frequencies. Channels at 166.0 and 183.31 ± 7 GHz are most sensitive to changing D o of cloud ice, channels at ≥89.0 GHz are most sensitive to changing D o of graupel, and at 18.7 and 36.5 GHz they show the greatest sensitivity to hail D o. Simulations contrasting BTs above high concentrations of small (0.5-cm diameter) and low concentrations of large (20-cm diameter) hailstones distributed evenly across a satellite pixel showed much greater scattering using the higher concentration of smaller hailstones with BTs as low as ~110, ~33, ~22, ~46, ~100, and ~106 K at 10.65, 18.7, 36.5, 89.0, 166.0, and 183.31 ± 7 GHz, respectively. These results suggest that number concentration is more important for scattering than particle size given a constant S-band radar reflectivity.

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