Observations of Storm Signatures by the Recently Modified Conical Scanning Millimeter-Wave Imaging Radiometer

摘要

The Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) is an airborne total-power radiometer that, after the recent modification, measures radiation at the nine frequencies of 50.3, 52.8, 89 (dual-polarized), 165 (dual-polarized), 183.3 $pm$ 1, 183.3 $pm$ 3, and 183.3 $pm$ 7 GHz. During the Mid-latitude Continental Convective Clouds Experiment of April 22–June 1, 2011, it is programmed to acquire radiometric measurements in both conical and cross-track scans nearly simultaneously. Its new capability of measuring scattering signatures from storm-associated hydrometeors in dual polarization at both 89 and 165 GHz is illustrated and reported in this paper. We find that, from all seven flights over stratiform rain and convective storms, the polarization index ($PI$), is small but definitively positive at both frequencies, and generally $PI(89 hbox{GHz}) leq PI(165 hbox{GHz})$. When brightness temperatures $T_{bp}$s are $geq$ 240 K, there is a significant correlation between $PI$ and the brightness difference between the two frequencies ($dT_{bp} = T_{bp}(89) - T_{bp}(165)$ , where $p$ is either vertical V or horizontal H polarization); linear regression between these two parameters gives positive slopes for all seven events, with 165-GHz slopes generally larger the 89-GHz ones. Observations fr- m five special sensor microwave imager/sounder passes in near concurrence with the CoSMIR measurements are examined for the relation between $PI(91.665 hbox{GHz})$ and $dT_{bh}$(91.665 GHz–150 GHz). The regression slopes are again found to be positive, and their magnitudes show some correspondence to those of CoSMIR. The significance of these findings to improvement in the parameter retrievals of hydrometeors is briefly discussed.