83rd Annual

Monday, 10 February 2003
On the small scale structure of convective precipitation
Thomas Hauf, University of Hannover, Hannover, Germany; and M. Theusner
Poster PDF (498.7 kB)
The cloud and precipitation fields behind cold fronts reveal a typical spatial structure of isolated clouds, closed or open cells, rolls or cloud cluster. We have used weather radar data from the German radar network and analyzed 39 days where cold fronts passed over Germany. From altogether 3258 radar scans we extracted about 140000 precipitating clouds and determined their length scale D, perimeter U, and area F, given by the lowest reflectivity value of 7dBZ and determined the frequency distributions and diurnal cycle of the various quantities. We distinguished between isolated cells with one radar reflectivity maximum and clusters with more than one maximum. We found that the ratio of isolated cells to cluster is approximately 2.6 and remains constant in the course of the day with only a slight variation of +/- 3%, despite of substantial variation in the respective numbers. We further show that the area-perimeter relationship follows a power law U**2 ~ F**b with a value of the fractal dimension of clouds b=1.359, identical with Lovejoy's analysis (1982) who found b=1.35. A closer look, however, reveals differences in the area-perimeter relationship between isolated cells and clusters which will be discussed further.

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