A Study of Heat and Moisture Budget Over the Arabian Sea and Their Role in the Onset and Maintenance of Summer Monsoon

Abstract

The influence of heat, moisture and moist static energy (MSE) budget, over the Arabian Sea and adjoining area (0*-30*N and 30*E-75*E), on the onset and activities of Asian summer monsoon has been studied in detail. The data base for this study consists of twice daily FGGE Level IIIb analysis for the period 16 May to 15 July 1979.The pentad mean variation, the vertical distribution and period averages of the various terms in energy budget equations are closely examined to find out their influence on the activities of monsoon. The study indicates the significant increase in the net enthalpy, latent heat energy (LHE), MSE and a number of budget parameters, well in advance of the onset of monsoon over Kerala coast. Further, a decreasing trend is observed in most of the above parameters about 5 days before the break monsoon condition which started over India on 16 July, 1979.The vertical distributions of the budget parameters reveal that during active monsoon period secondary maxima of horizontal heat and MSE flux divergences are observed in the upper troposphere which are replaced by minima during weak monsoon circulation. The broad features of the budget studies over the Arabian Sea are in good agreement with the large scale energetics (Mohanty et al. 1982a(Mohanty et al. , 1982b. Some of the significant departures in the results of the two studies have been discussed.

The contrasting features of Asian summer monsoon during surplus and deficient rainfall over India

“…Both, in turn, give rise to profound cumulus convection and an increase in tropospheric diabatic heating. This leads to the formation of a strong thermal gradient, and the whole circulation continues to intensify through a positive moisture feedback to maintain the monsoon circulation (Mohanty et al, 1983;Pearce and Mohanty, 1984). Further, the interaction between the large-scale flow and moisture convection over the monsoon domain is poorly understood.…”

Onset characteristics of the southwest monsoon over India

“…Some of the well-known features are a rapid increase of daily precipitation, vertically integrated moisture and an increase in the kinetic energy in the lower levels (Mohanty et al, 1983). In this section, the circulation features of the Asian summer monsoon have been studied with composites of the three different pentads during the evolution of the monsoon over India.…”

“…These include the northward displacement of upper tropospheric westerly flow to the north of the Himalayas, establishment of the upper tropical easterly jet (TEJ) stream (Koteswaram, 1958) and lower tropospheric westerly jet (Somali jet) over the Arabian Sea (Findlater, 1969). The intensification of the monsoon flow is mainly dictated by the release of convective instability and tropospheric diabatic heating (Krishnamurti and Ramanathan, 1982;Mohanty et al, 1983;Pearce and Mohanty, 1984;Rao and Aksakal, 1994). Studies by Soman (1988, 1989) and Soman and Krishnakumar (1993) documented the climatological structure of the meteorological fields associated with the onset phase of the summer monsoon.…”

Energy Transformations in the Tropical Circulation During the FGGE Winter

“…The initialized vertical velocity field obtained from the adiabatic non-linear normal mode initialization and stored in FGGE data sets of ECMWF does not represent the true vertical motion in the tropics (Kanamitsu, 1981;Mohanty et al, 1983). Further, an intercomparison of the global vertical motion in both ECMWF and GFDL data sets during SOP-I and SOP-II periods by Kung et al (1983) indicates that the vertical motion of the ECMWF level-IIIb analyses is underestimated mainly over the rising branch of the Hadley circulation in comparison with that of GFDL archives.…”