Tropical Convection and Precipitation

Strategic Element: Healthy Ecosystems

Principal Investigator: Frank D. Marks

Objective: Basic physical understanding, quantitative estimation and forecasts of tropical precipitation. Observational studies with radar aircraft and surface instruments.

Narrative: The goal of this project is estimation of the direct freshwater flux from rainfall into Florida Bay, and the indirect flux from rain north of the Bay. The small spatial scale of convective rainfall, combined with wide separation of rain gages, make the new WSR-88D Doppler weather radars an essential tool for this undertaking. The chief advantage of radar is large area coverage with high spatial and temporal resolution. Nonetheless, measurement of surface rainfall rates with radar is not without problems.

To fully exploit the new radars' hydrological potential, their rainfall estimation algorithms---which were developed for mid-latitude regimes---must first be tuned for the tropical conditions. While the WSR-88D provides the best high resolution estimate of the fresh water contribution from direct rainfall, routine comparisons with surface rain gages are an essential check on the overall radar performance. The recently developed probability matching method derives the relationship between observed radar reflectivities and rainfall rates concurrently measured from drop size distributions. This method constrains the reflectivity--rainfall function so that the probability density functions of the radar data and the drop size distributions match. It allows actual radar data to be compared with simultaneous rainfall data, even at large ranges. Proper archival of the digitally recorded data record is required for this new tool to be useful to Florida Bay researchers.

Duration: 1996 through the present.

Reference:

Marks, F. D., 1990: Radar observations of tropical weather systems, Radar in Meteorology, D. Atlas, ed, American Meteorological Society, Boston, 401--425.

Investigations:

RECONSTRUCTION OF SURFACE WIND FIELDS FOR TROPICAL CYCLONES AFFECTING FLORIDA BAY

DROP DISTORTIONS NEAR LARGE AIRCRAFT AS OBSERVED BY 2-D PARTICLE IMAGE PROBES

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