STRUCTURE OF FLORIDA THUNDERSTORMS USING HIGH-ALTITUDE AIRCRAFT RADIOMETER AND RADAR OBSERVATIONS

This paper presents an analysis of a unique radar and radiometer datas et from the National Aeronautics and Space Administration (NASA) ER-2 high-altitude aircraft overflying Florida thunderstorms on 5 October 1 993 during the Convection and Moisture Experiment (CAMEX). The observa tions represent the first ER-2 Doppler radar (EDOP) measurements and p erhaps the most comprehensive multispectral precipitation measurements collected from a single aircraft. The objectives of this paper are to 1) examine the relation of the vertical radar reflectivity structure to the radiometric responses over a wide range of remote sensing frequ encies, 2) examine the limitations of rain estimation schemes over lan d and ocean backgrounds based on the observed vertical reflectivity st ructures and brightness temperatures, and 3) assess the usefulness of scattering-based microwave frequencies (86 GHz and above) to provide i nformation on vertical structure in the ice region. Analysis focused o n two types of convection: a small group of thunderstorms over the Flo rida Straits and sea-breeze-initiated convection along the Florida Atl antic coast. Various radiometric datasets are synthesized including vi sible, infrared (IR), and microwave (10-220 GHz). The rain cores obser ved over an ocean background by EDOP, compared quite well with elevate d brightness temperatures from the Advanced Microwave Precipitation Ra diometer (AMPR) 10.7-GHz channel. However, at higher microwave frequen cies, which are ice-scattering based, storm evolution and vertical win d shear were found to be important in interpretation of the radiometri c observations. As found in previous studies, the ice-scattering regio n was displaced significantly downshear of the convective and surface rainfall regions due to upper-level wind advection. The ice region abo ve the rain layer was more opaque in the IR, although the 150- and 220 -GHz brightness temperatures T-b approached the IR measurements and bo th corresponded well with the radar-detected ice regions. It was found that ice layer reflectivities and thicknesses were approximately 15 d BZ and a few kilometers, respectively, for detectable ice scattering t o be present at these higher microwave frequencies. The EDOP-derived r ainfall rates and the simultaneous microwave T-b's were compared with single-frequency forward radiative transfer calculations using a famil y of vertical cloud and precipitation water profiles derived from a th ree-dimensional cloud model. Over water backgrounds, the lower-frequen cy emission-based theoretical curves agreed in a rough sense with the observed radar rainfall rate-T-b data points, in view of the uncertain ties in the measurements and the scatter of the cloud model profiles. The characteristics of the ice regions of the thunderstorms were exami ned using brightness temperature differences Delta T-b such as T-b (37 GHZ) - T-b (220 GHz). The Delta T-b's (150-220, 89-220, and 37-86 GHz ) suggested a possible classification of the clouds and precipitation according to convective cores, elevated ice layers, and rain without s ignificant ice above the melting layer. Although some qualitative clas sification of the ice is possible, the quantitative connection with ic e path was difficult to obtain from the present observations.