Kinetic Energy Sources in Large-Scale Tropical Disturbances Over the Marshall Islands Area

Abstract

The maintenance of large-scale tropical disturbances has been examined with the source terms of kinetic energy generation utilizing the special 1958 upper-air observations in the Marshall Islands area. An optimized objective analysis scheme for the computation of kinematic vertical velocity as well as the method for evaluation of energy variables is presented. The time mean budgets of kinetic energy source terms are presented in terms of vertical profiles and intensity of processes represented by each term. The eddy conversion of available potential energy has its primary maximum in the layer between 400 and 200 mb, whereas the eddy kinetic energy generation shows maxima in the lower boundary and upper troposphere between 200 and 100 mb. In terms of the time mean budget only a fraction of the released energy by eddy conversion contributes to the eddy generation of kinetic energy in the area. Through examination of the time series of energy variables, it is revealed that horizontal eddy flux convergence of potential energy is the dominant term in determining the local generation of eddy kinetic energy. The migration pattern of the ITCZ further suggests that this horizontal eddy flux term is closely associated with the position of the ITCZ, with a significant divergence of eddy flux of potential energy when the ITCZ is located to the south of the area.