A comparison of optical rain gauge and radar data from TOGA/COARE

A comparison between rain gauge data and radar data from the Tropical Oceans Global Atmosphere/Coupled Ocean Atmosphere Response Experiment (TOGA/COARE) was studied. The rain gauge data from an echo that passed over the Xiangyanghong #5 on December 24, 1992 was compared to what the MIT radar saw at this location from the R/V Vickers, 103.4 km to the east. The precipitation measured by the rain gauge peaked at 108 mm/hr 92 seconds into the period before tapering off 11 1/2 minutes later. This sharp gradient was evident in a PPI plot of the radar reflectivities and the percentage area-rainfall for the radar data statistics. The percentage area curve was converted to rain rates using a GATE Z-R and compared to a percentage time curve of rain rates according to the rain gauge. A four minute running average applied to the rain gauge rates improved the comparison of peak rates between the rain gauge and radar. Differences in peaks between rain rates observed by the rain gauge and reflectivities observed by the radar could be due to variations in rainfall rates within a single radar data bin. For example, two measurements of reflectivity such as 37 and 47 dBZ within the same bin would result in a 44 dBZ average. This range in rates from 12 mm/hr to 74 mm/hr is observed in 30 seconds by the rain gauges within the first two minutes of the radar echo passage.