THE EFFECT OF RAIN ON AIR-WATER GAS-EXCHANGE

The relationship between gas transfer velocity and rain rate was inves tigated at NASA's Rain-Sea Interaction Facility (RSIF) using several S F6 evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with 18 diff erent rain rates (7 to 110 mm h(-1)) and 1 of 2 dropsizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-w ater gas exchange by rainfall. The gas transfer velocities derived fro m our experiment were related to the kinetic energy flux calculated fr om the rain rate and dropsize. The relationship obtained for mono-drop size rain at the RSIF was extrapolated to natural rain using the kinet ic energy flux of natural rain calculated from the Marshall-Palmer rai ndrop size distribution. Results of laboratory experiments at RSIF wer e compared to field observations made during a tropical rainstorm in M iami, Florida and show good agreement between laboratory and held data .