Characteristics of clouds and precipitation in the Western Indian monsoon regime
Abstract
The rainfall and raindrop size distribution measured with JW-Disdrometer has been utilized to study the characteristic features of precipitation during the monsoon and post-monsoon months over two tropical stations of India, i.e., Pune (sea-surface height = 560 m; annual rainfall = 660 mm) and Mahabaleshwar (sea-surface height = 1438 m; annual average rainfall = 8000mm) along the Western Ghat mountain range. The stations show distinct pattern of raindrop size distribution and other integrated rainfall parameters during the two seasons. The factors affecting these variations have also been discussed in the present paper. A case study of two rain events over Pune on July 31, 2012 and October 26, 2012 of nearly same rain rate (~ 60 mm/hr) have been made to characterize the monsoon and post monsoon rainfall respectively. It is clearly seen from the analysis that the drops of larger diameter dominates the post monsoon month over Pune whereas smaller drops shows its prominent presence in the monsoon months for nearly same rain rate. This is because, the rain in the month of October is basically convective in nature, as result of which the presence of strong updraft carries the smaller drops that are having the fall velocities smaller than the drafts to the higher altitude, thereby allowing the bigger drops to precipitate locally Such conditions are very rarely seen in the monsoon rainfall i.e. during the month of July. In order to get into the more insight about the rainfall pattern, 4 different rain events have been chosen from the above two stations, i.e Pune and Mahabaleshwar and they are classified as convective and stratiform rainfall on the basis of certain parameters. The events which has been considered as stratiform rainfall have the rain rate in the range of 0.5-5 mm/hr and standard deviation of rain < 1.5 whereas the rain events which has been considered as convective rainfall has the rain rate > 5 mm/hr and standard deviation of rain > 1.5. By taking the above concept, a plot has been made between the mass-weighted mean diameter (Dm) and intercept parameter (Nw). The calculation of Dm and Nw has been given in Bringi et al., 2003. It is very much visible from the above analysis that an inverse relationship exists between log10Nw and Dm for the stratiform rain events. From microphysics point of view, it is well known that stratiform rain results via the melting of snowflakes and/or tiny grupel or rimed particles. Thus the presence of bright band reflects the melting of larger, low density and dry snowflakes into rain which ultimately leads to DSDs that have smaller <Nw> and larger <Dm>. Such distinct features are absent in case of convective precipitation. Reference : Bringi, V.N., V.Chandrasekar, J.Hubbert, E.Gorgucci, W.L.Randeu and M.Schoenhuber (2003), Raindrop size distribution in different climatic regimes from Disdrometer and dual-polarized radar analysis, J. Atmos. Sci., 60, 354-364.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A43B0239C
- Keywords:
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- 0320 ATMOSPHERIC COMPOSITION AND STRUCTURE Cloud physics and chemistry