Sunday, 10 August 2003: 11:30 AM
An algorithm for estimating the variance of the canting angle distribution using polarimetric covariance matrix data
It is well known that turbulence and multi-mode drop oscillations can effectively increase the variance of the raindrop canting angle (b) distribution, especially in heavy rain conditions where collisional forcing of drop oscillations may be important. While the exact from of the canting angle distribution resulting from multi-mode oscillations is not known, it may be assumed that it is symmetric about the mean of 0o. Under these conditions it is possible to derive an estimator of sb using the ratio of the minimum and maximum cross-polar power (Hendry, Antar and McCormick). This ratio can be calculated from the measured covariance matrix. We use data from the CSU-CHILL radar to show how sb varies with Zdr in several convective rain events. The data show that sb decreases with increasing Zdr implying that larger drops are more ‘stably’ oriented as opposed to smaller ones. The retrieval of dsd parameters and rain rate using the estimate of sb will be discussed.