Observations and modelling of radiometric signatures of storms in the frequency range of 90-220 GHz

Abstract

During the past three years, a number of observations have been made with an airborne millimeter-wave imaging radiometer (MIR) over the storms in the western Pacific Ocean and in the coastal region of the eastern United States. MIR measured radiometric signatures of these storms at six frequencies of 89, 150, 183.3/spl plusmn/1, 183.3/spl plusmn/3, 183.3/spl plusmn/7, and 220 GHz. Analyses of these measurements show that brightness temperatures (T/sub b/) at all frequencies are strongly depressed. In some cases the T/sub b/ depression displays a strong frequency dependence of scattering by hydrometeors. In other cases there is a leveling off of scattering at high frequencies, i.e., Tb values at 150 and 220 GHz are quite comparable. A few high-towering scattering cells are found to display unique signatures at the three water vapor channels near 183.3 GHz which in turn could be used to identify these cells. A series of calculations with a backward Monte Carlo technique, using profiles of hydrometeors generated by a cloud model, are performed to simulate some of these observed features. Results from these calculations are compared with observations and their implications on the storm structures are discussed.