On the Accuracy of a Precipitation Coverage Index Computed from Radar Reports

Abstract

The Radar Index (RI) is presented as a statistic used to study convective activity in the summer monsoon over southeast Asia. The RI is defused simply as the percent coverage of echo within 50 n mi of the radar. A computer technique is described which accepts coded radar reports (RAREPS) as input, calculates the RI, and plots the original RAREP. Hourly values of the RI have been calculated for four summers in southeast Asia. This approach to radar data has a number of limitations. The technique is critically examined by comparing values of the RI computed from RAREPS with those found directly from PPI scope photography and also with hourly rainfall data. The RI estimates the probability of rain better than the total rainfall. The major drawback of this technique is inaccurate RAREPS. The major advantages are application to areas with limited rainfall data and the speed with which months of data can be processed on a computer.