Experimental analysis of microscale rain cells and their dynamic evolution

This paper presents a detailed space-time analysis of rainfall rate using two dense networks of rain gauges covering two microscale areas of some 100 km2 each and located in two distinct climatic areas in the United Kingdom and Spain. The study has been carried out with the main objective of addressing dynamic fade mitigation techniques and scatter interference problems in terrestrial and satellite communication systems. The two databases, using a total of 49 and 23 rain gauges, respectively, are described, and the continuous interpolated field used for the subsequent analyses is explained in detail. The suitability of the networks in terms of density, correlation distance, and fractal dimension are briefly addressed. A to-scale comparison grid of the networks is also given. It has been found that when the maximum intensity reached during a rain event surpasses a certain threshold, different for each of the two areas, rainfall rates exhibit a spatial structure in the form of closed contours of thresholds referred to as cells. In statistical terms, the most probable diameter found is about 3.5 km, and distributions are presented. They are similar for the two sites but not so for the maxima reached inside the cells. Using cross-correlation techniques, displacement and velocities are analyzed in detail. Cells “zigzag” around a dominant trend because of the global cloud movements (driven by winds at heights of about 700 hPa). Local topography strongly affects local behavior. Analytical approximations to the experimental statistical distributions and selected histograms of the results are presented.