Journal of the Meteorological Society of Japan, 78, 167-173.

On the dynamics of easterly waves, monsoon depressions, and tropical depression type disturbances

Adam H. Sobel
Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY.

Takeshi Horinouchi
Radio Atmospheric Science Center, Kyoto University, Uji, Japan


The authors argue that certain aspects of the rotational, synoptic-scale disturbances of the wind field that are observed in ITCZ or monsoon trough regions can be understood by considering the linear response of a dry, initially resting atmosphere to a pulse of heating whose amplitude and spatial and temporal scales are characteristic of a large mesoscale convective system. The key points are that short Rossby waves have small intrinsic group and phase velocities, and that a heating pulse projects much more energy on the Rossby modes if it is located off rather than on the equator. It follows that synoptic-scale Rossby waves, with characteristics broadly similar to those of observed disturbances, should be present in off-equatorial regions of persistent deep convection, since large mesoscale convective systems tend to develop in such regions.