Rain drop size distributions (DSD's) are formed by precipitation processes at many levels in the atmosphere, and besides being important in their own right - the moments of the distributions are directly related to liquid water content, rainfall rate (R), and radar reflectivity factor (Z). As part of a product to refine a WSR-88D (NEXRAD) radar rainfall product for South Florida, a continuous record of one minute have been obtained from a disdrometer at a site in the Everglades. In numerous cases to improve agreement between radar rain estimates and gage values, the National Weather Service has invoked a "tropical Z-R, yet the standard NEXRAD Z-R (Z=300R1.4) was first developed from rainfall measurements near Miami.
The record of Everglades DSD's is analyzed and the resultant Z-R relationships are compared to the NWS tropical Z-R relationship. The sample is partitioned into a convective and stratiform fractions., and mean DSD's derived for rain rate intervals. The high rainfall rate sample of DSD's, even though presumably all convective, exhibit a rather wide range of behavior (shape), and a rather wide range of Z for the same rainfall rate. The radar echo structure, and history of development, is examined for this range of DSD shape categories. In addition to the areal change of DSD shapes, radar-gage disagreement is often attributed to systematic changes in the DSD's from aloft, where the radar measurement is of necessity made, to the surface, where the gage measurement is made. The distributions of radar reflectivities for the first four elevation scans is examined for any systematic changes, and by implication, changes in the DSD's during the fall of the rain to the surface.