Sensitivity of the Monsoon Onset to Differential Heating

Abstract

This paper examines some observational aspects of the evolution of energy exchanges and differential heating during the GARP Monsoon Experiment MONEX. The main findings are that: 1) A large increase in the kinetic energy of the total flow field and the nondivergent component of the flows occurs over the Arabian Sea about a week prior to the onset of monsoon rains over central India. 2) The field of differential heating moves during the onset period to a favorable position for the generation of eddy available potential energy and its release to eddy kinetic energy. 3) The release of the eddy available potential energy goes to enhance the kinetic energy of the divergent circulations. 4) The kinetic energy of the divergent circulation does not increase much with time. This energy is shown to he transferred rapidly to the nondivergent motion via a number of interaction functions. The orientation of the divergent flows is shown to be of prime importance in these transfers during the onset, active, break and revival periods of the monsoons. Based on the above observational findings a series of numerical prediction experiments ire conducted to examine the sensitivity of the monsoon onset to initially imposed fields of differential heating. The results of some 96 h integrations seem to confirm the large sensitivity in the evolution to the field of heating. The results of time integrations also show that the kinetic energy of the monsoon circulations increases via the rapid increase of interactions among the irrotational and nondivergent modes.