MICROWAVE AND INFRARED SIMULATIONS OF AN INTENSE CONVECTIVE SYSTEM AND COMPARISON WITH AIRCRAFT OBSERVATIONS

A three-dimensional cloud model, radiative transfer model-based simula tion system is tested and validated against the aircraft-based radianc e observations of an intense convective system in southeastern Virgini a on 29 June 1986 during the Cooperative Huntsville Meteorological Exp eriment. NASA's ER-2, a high-altitude research aircraft with a complem ent of radiometers operating at 11-mu m infrared channel and 18-, 37-, 92-, and 183-GHz microwave channels provided data for this study. The cloud model successfully simulated the cloud system with regard to ai rcraft- and radar-observed cloud-top heights and diameters and with re gard to radar-observed reflectivity structure. For the simulation time found to correspond best with the aircraft- and radar-observed struct ure, brightness temperatures T-b are simulated and compared with obser vations for all the microwave frequencies along with the 11-mu m infra red channel. Radiance calculations at the various frequencies correspo nd well with the aircraft observations in the areas of deep convection . The clustering of 37-174-GHz T-b observations and the isolation of t he 18-GHz values over the convective cores are well simulated by the m odel. The radiative transfer model, in general, is able to simulate th e observations reasonably well from 18 GHz through 174 GHz within all convective areas of the cloud system. When the aircraft-observed 18- a nd 37-GHz, and 90- and 174-GHz T-b's are plotted against each other, t he relationships have a gradual difference in the slope due to the dif ferences in the ice particle size in the convective and more stratifor m areas of the cloud. The model is able to capture these differences o bserved by the aircraft. Brightness temperature-rain rate relationship s compare reasonably well with the aircraft observations in terms of t he slope of the relationship. The model calculations are also extended to select high-frequency channels al 220, 340, and 400 GHz to simulat e the Millimeter-wave Imaging Radiometer aircraft instrument to be flo wn in the near future. All three of these frequencies are able to disc riminate the convective and anvil portions of the system, providing us eful information similar to that from the frequencies below 183 GHz bu t with potentially enhanced spatial resolution from a satellite platfo rm. In thin clouds, the dominant effect of water vapor is seen at 174, 340, and 400 GHz. In thick cloudy areas, the scattering effect is dom inant at 90 and 220 GHz, while the overlying water vapor can attenuate at 174, 340, and 400 GHz. All frequencies (90-400 GHz) show strong si gnatures in the core.