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In order to make the process more quantitative, we have also calculated the cross-correlationcoefficient between the two parameters, and the results are shown in fig. 4.Fig. 4. Cross-correlation between the isotropy index and the precipitation index.The cross-correlation coefficient at zero lag is 0.656, and it is in fact slightly larger at a lag of3-4 hours, being 0.722 at the peak. Typically there are about 200 points per correlation,although this number varies depending on the degree of overlap of data in the two data sets(in some cases one or other parameter had missing data). The 95% confidence limits on theseestimates are 0.570 and 0.723 at zero lag, and 0.652 and 0.782 at a lag of 3 hours, indicatinga strong correlation. The fact that the cross-correlation function peaks at a temporal lag of 3-4hours arises because the isotropy parameter usually reaches values of 20 o before theprecipitation arrives, as discussed in regard to fig. 3.It therefore appears that the aspect-sensitivity parameter is often a precursor to precipitation.We expect that the reason for this is because much of the non-winter rain arises due toconvection, and we expect enhanced convection to correspond to greater isotropy for theturbulent eddies. We envisage that the convection may encompass a much larger area thanthe precipitation, with the region of precipitation embedded inside it. This explains why theenhanced anisotropy precedes the precipitation – it covers a larger area, and so as the regiondrifts across the radars, the outskirts, where there is no precipitation, cross the radars first.We plan to extend this study to cover a longer time-frame.Acknowledgments:We especially acknowledge the support of Prof. Isztar Zawadzki, Director, J.S. MarshallRadar Observatory, Dept. of Atmospheric and Oceanic Sciences, McGill University, Canada.References:Campos, E., and W. Hocking, Vortical Motions observed with..., this issue.Gage, K.S., and J.L. Green, Evidence for specular ..., , Radio Sci., 13, 991-1001, 1978Hocking W.K. Radar studies of small ..., Advances in Space Res., 7(10), 327-338, 1987.Hocking, W.K. Target Parameter Estimation, MAP Handbook, 30, 228-268, 1989.Hocking, W.K., et al., Aspect sensitivity of stratospheric..., Radio Sci., 25, 613-627, 1990Hocking, W.K., and A.M. Hamza, , J. Atmos. Solar Terr. Phys., 59, 1011-1020, 1997.Hooper, D., and L. Thomas, Aspect sensitivity of..., J. Atmos. Terr. Phys., 57, 655-663, 1995.Roettger, J., and C.H.Liu, Partial reflection and..., Geophys. Res. Lett., 5, 357-360, 1978Tsuda, T., et al., MU radar observations of the aspect ..., Radio Sci., 21, 971-980, 1986.447