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  • Author or Editor: R. Raghavan x
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D. R. Sikka and K. Raghavan

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S. Raghavan, T. R. Sivarmakrishnan, and B. Ramakrishnan

Abstract

A study of the size distribution of radar echoes from precipitating clouds around Madras during the southwest and northeast monsoon seasons shows a preponderance of echo sizes in the D scale (up to 100 km2) with relatively small percentages in the C scale (101 to 1000 km2) and in the B/C scale (>1000 km2). The largest echo size observed was 21 000 km2. If the cumulative percentage frequencies of areas of cells are plotted on logarithmic probability paper, the smaller cells constituting 85–95% of the total population are seen to follow a lognormal distribution. In the larger size ranges, however, systematic deviations on either side of the lognormal graph occur.

The lognormal distribution points to a growth mechanism of convective cells by a process whereby growth at every step is a random proportion of the initial size. The deviations from the lognormal distribution in the land area in the northeast monsoon season indicate limitation of growth after the cells which develop over the sea drift over the land. In the southwest monsoon season and in the sea area during the northeast monsoon, growth is found to occur to very large sizes more often than a lognormal distribution would predict. The deviation from lognormality appears to be due to development of a stratiform mesoscale anvil cloud similar to the model of Leary and Houze in the Global Atmospheric Research Program's (GARP) Atlantic Tropical Experiment (GATE).

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J. Vivekanandan, V. N. Bringi, and R. Raghavan

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This paper uses a microphysically detailed graupel and hail melting model, described by Rasmussen and Heymsfield, which is coupled to a radar model that computes multiparameter variables such as differential reflectivity, linear depolarization ratio, the specific propagation differential phase shift and X-band specific attenuation. The microphysical model is initialized with two different summer-time sounding profiles (Colorado and Alabama). Sensitivity studies are performed with respect to particle shape and orientation distributions. The hail melting model is also initialized with a summertime sounding from the Munich, FRG area, and C-band differential reflectivity is computed for application to radar data from the DFVLR radar. A simple spherical hail melting model is also used to study the effects of absorption and scattering on the X-band attenuation. NCAR CP-2 radar measurements from the MIST (Microburst and Severe Thunderstorm) project and from CINDE (Convective Initiation and Downburst Experiment) are used to illustrate the usefulness of multiparameter data in studying the melting of ice in convective storms.

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