Mean dynamical characteristics of the Asian summer monsoon with a global analysis - Forecast system

The dynamical characteristics of Asian summer monsoon are examined with a g lobal spectral model. In addition to the seasonal circulation features, the large scale budgets of kinetic energy, vorticity and angular momentum are examined making use of mean analysis and forecast fields (upto day 5) for s ummer season comprising June, July and August, (JJA) 1994. Apart from eluci dating the systematic errors over the monsoon region, the study expounded t he influence of these errors on associated dynamics. The significant errors in the low level how (850 hPa) evince (i) weakening of south easterly trades and cross equatorial flow into the Northern Hemisp here and (ii) weakening of westerly flow over the North Indian Ocean. Simil arly, in the upper level flow (200 hPa) they indicate (i) weakening of Tibe tan anti-cyclone and (ii) reduction of return flow into the Southern Hemisp here. The balance requirements in the mean analysis as well as forecast fields ar e fairly in agreement with the observed over the summer monsoon. The monsoo n domain is discerned as the source region of kinetic energy and vorticity. Both are produced in the monsoon region and transported horizontally acros s. The model forecasts fail to retain the analyzed atmospheric variability in terms of mean as well as transient circulations which is revealed by kin etic energy budget. This is further corroborated by vorticity and angular m omentum budgets. It is noticed that the forecasts in all ranges produce fee ble monsoon circulation which weakens considerably with increase in the for ecast period.