The Energetics of Asian Summer Monsoon

Abstract

Ð In this paper, we examine the large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture over the Asian summer monsoon region. The ®ve year (1986±1990) uninitialized daily analyses for the summer season comprising June, July and August (JJA), produced at the European Centre for Medium Range Weather Forecasts (ECMWF) under the aegis of Tropical Ocean and Global Atmosphere (TOGA) have been considered to carry out the study.The following features characterize the Asian summer monsoon domain. It acts as the source of kinetic energy as well as vorticity, and sink of heat and moisture. Kinetic energy and vorticity are produced in the monsoon region and transported horizontally. On the contrary, heat and moisture are transported into the monsoon region. The zonal and meridional components of adiabatic generation of kinetic energy contribute to the production of kinetic energy over the Arabian Sea and Bay of Bengal, respectively. The horizontal advection of relative vorticity is balanced by sub-grid scale generation. The angular momentum generated due to pressure torque (east-west pressure gradient) is balanced by the¯ux convergence of omega momentum. Further, the angular momentum budget delineates that¯ux convergence of relative momentum is necessary to maintain the surface westerlies against the friction. The horizontal convergence of heat and moisture facilitates enhancement of diabatic heating, and also leads to the formation of diabatic heat sources, which are crucial to sustain the summer monsoon circulation.

Himalayan rainfall and vorticity generation within the Indian summer monsoon

“…The generation of vorticity within the Indian monsoon region is crucial for maintaining the monsoon circulation [ Rao , 2001]. The Himalayas are thought to be an integral part of this complex monsoon dynamics [ Webster et al , 1998], however there have been few studies looking at the role of Himalayan rainfall in the Indian monsoon, partly due to rainfall in the region not being well quantified until recent years [ Lang and Barros , 2002].…”

The vorticity and angular momentum budgets of Asian summer monsoon

“…Earlier studies (Mohanty and Ramesh 1994;Rao 2001) sets the effect of omega momentum flux in the balance of angular momentum. This aspect is in agreement with the earlier observations (Mohanty and Ramesh 1994;Rao 2001).…”

“…) adduced this aspect. Although, some studies addressed the issue of the large-scale balances of vorticity and angular momentum over Asian summer monsoon (Oort and Chan 1977;Fein 1977;Mohanty and Ramesh 1994;Rao 2001), very few elucidated the maintenance of Asian summer monsoon during the evolution and established phases and compared it in various reanalyses/analyses. In this vein, this study aims to enunciate the maintenance of Asian summer monsoon through vorticity and angular momentum budgets.…”

A Note on the Maintenance of Asian Summer Monsoon Circulation

“…The various budget equations considered are similar to those expressed in earlier studies Vol. 160, 2003 Maintenance of Asian Summer Monsoon Circulation 2449 (RAO, 2001). In this study, the energy budgets are computed using daily reanalysis/ analysis fields.…”

“…Although certain aspects of the maintenance of Asian summer monsoon (OORT and CHAN, 1977;MOHANTY et al, 1983;PEARCE and MOHANTY, 1984;RAO, 2001) were addressed, most of them are case studies. Despite providing basic information on maintenance of summer monsoon, these studies evinced the need to comprehend the myriad facets of the summer monsoon.…”