The inclusion of Himalayas in a primitive equation model

Abstract

A regional primitive equation model has been developed for the Indian region. One of the difficulties in this model is caused by large gradients in mountainous regions. To avoid large truncation errors near the edges of mountains, some models evaluated the pressure gradient force on a constant pressure surface, instead of a sigma surface. More recently, phillips (1974) suggested that truncation errors could be reduced by removing the hydrostatic component of the geopotential field, The resiciual geopotential may then be treated as a dependent variable, which could be integrated with respect to time by the model. To be energetically consistent, a temperature field was similarly defined. This paper discusses the scheme for the Himalayan region. Truncation errors by the present scheme are compared with the earlier method. The conversion from sigma to pressure coordinates was carried out by Lagrangian interpolation. Results are presented with these methods to show the development of circulations in 5 days of model time.