Pressure-Wind Relationships in the Equatorial Surface Westerlies

Abstract

Seasonally persistent westerly winds at the surface in the vicinity of the equator from 40E to 170E longitude are shown to be the generally predictable result of a geostrophically appropriate pressure gradient at latitudes higher than about 5° north or south, and a negative value of the second derivative of the pressure with latitude within about five degrees latitude of the equator. Existing empirical equatorial wind-pressure relationships are shown to be specific cases of these general relationships. The initiating mechanism for equatorial westerlies seems to be a movement of the equatorial trough more than five degrees of latitude from the equator.