A statistical study of Melbourne radar rain echoes

This paper analyses a large number of radar rain echoes observed from Aspendale, near Melbourne, over more than four years; 6109 echoes were logged and tracked for half an hour or longer. These have been studied in their synoptic setting, and statistically analysed with the help of Bureau of Meteorology routine surface and aerological observations and analysed charts. Frequency distributions are given relating to echo lines and individual echoes in them; velocity, echo-related rainfall; vertical temperature and humidity profiles; cloud base and top; stability index; and upper winds, both absolute and relative to echoes. The differing statistics for echo days, dry days and thundery days are examined for diagnostic value. Vector correlation between echo velocity and upper wind at various heights is computed to exceed 0.9 overall in the lowest levels. Density weighted mean winds over a vertical thickness of the order of 3 km provide a prediction scheme based on regression equations, with standard vector errors of about 5 m-1. The lowest possible standard error achievable with the radar techniques used is about 3 m s-1.