A meso-scale three-dimensional dynamical model of orographic rainfall |
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Authors: | S Dutta |
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Institution: | (1) SAARC Meteorological Research Centre (SMRC), Agargaon, Dhaka, Bangladesh |
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Abstract: | Summary A mesoscale three-dimensional (3-D) dynamical model is presented to diagnose orographic rainfall, with particular reference
to the Western Ghats (WG) in India. This model has two parts, namely, a dynamical part and a thermodynamical part. In the
dynamical part the vertical velocity induced by a mesoscale elliptical orographic barrier has been computed using the perturbation
technique. In the thermodynamical part rainfall intensity (RFI) has been computed using the computed vertical velocities,
with the help of continuity of moisture and mass. The computed RFI has been compared with observed RFI as well as with that
computed by 2-D model.
The present study shows that during the southwest monsoon season (SWMS), orographic rainfall enhancement in the WG area appears
to be solely due to the vertical shear of the basic flow and its variation with height. Stability appears to have very little
influence on it.
The spatial distribution of RFI across the barrier shows that there are four regions of maximum rainfall, one primary on the
windward side behind the peak of the barrier and three secondary on the leeward side. The symmetry in the locations of these
secondary rainfall maxima appears to be critically dependent on the component of basic flow parallel to the major ridge axis
of the barrier. |
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Keywords: | |
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