Simulation of monsoon circulation and cyclones with different types of orography
Keywords:Digital filters, Envelope orography, Gibbs' oscillation, Window functions, Spherical harmonics, Global Spectral Model, Simulation, Numerical experiments.
In this study a number of sensitivity experiments have been conducted with different types of orography in the ECMWF spectral General Circulation Model (GCM). The basic aim is to simulate the large scale features of the Indian summer monsoon and the movement of cyclones. Different types of digital filters have been used to represent the orography as close to the observed values as possible. A comparative study shows that the Lanczos filter gives the best results. Thus, the Lanczos filter has been used in subsequent sensitivity experiments. One cyclone over the Bay of Bengal during pre-monsoon month of May, and another during the must active month of August have been selected for numerical experiments.
The large scale features of the monsoonal rainfall were found to be close to those observed, when standard deviation envelope orography was used. After 3 days of model integration, the rainfall distribution improved compared to the initial stages of integration. Although the predicted cyclone followed the observed track, the rate of movement was very sluggish. There was slight deepening of the systems with an increase of orography The movement of the systems was also found to be slightly faster with the enhancement of orography.
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