An observational study of 300 mb winds in the tropical belt. Part I: Kinematic parameters

Abstract

This study is diagnostic in character and entails a systematic investigation of the kinematic parameters of the mean monthly 300 mb horizontal-motion field for the global tropical region during January, April, and October.

The kinematic parameters analysed include the horizontal velocity divergence, relative vorticity, velocity potential, and stream function. The magnitude of relative voritcity has been observed to be nearly equal to that of the horizontal velocity divergence in the equatorial latitudes and an order of magnitude larger in the subtropics. The magnitudes of∂u/∂x, ∂v/∂y, and horizontal velocity divergence are comparable and vary very little with latitude, while that of∂u/∂y is an order of magnitude larger than that of∂v/∂x, confirming its dominance in the computation of relative vorticity.

The latitudinal position of zero absolute vorticity isopleth fluctuates within 5 degrees of the equator and is confined more to the winter hemisphere than to the summer hemisphere.

The rotational component of wind is large compared with the divergent wind component. The magnitude of the rotational vector wind is four times that of the divergent vector wind in the equatorial latitudes and an order of magnitude larger in the subtropical latitudes.