A preliminary Investigation of the Daily Meridional Transfer of Atmospheric Water Vapour between the Equator and 40° N

Abstract

As a preliminary investigation into the daily variation of the meridional flux of atmospheric water vapour between the equator and 40° N, the transport has been computed from the analysed fields of specific humidity (q) and the v-component of the wind field. The analysis is based on the observations taken at a single synoptic time. The computations confirm earlier results that the bulk of the flux takes place between the 850 mb pressure surface and the surface of the earth. Between the 500 mb pressure surface and the upper limits of the Hadley and Ferrel cells the flux amounts to about 10 % of the total flux.

It is further shown that the Hadley cell circulation is the most important agent for transporting water vapour equatorward. North of 30° N the eddy flux is the dominant factor but appears to be of a much weaker intensity than the Hadley cell flux.

The computed values of the difference between the zonally averaged evaporation and precipitation (E – P), for five-degree latitude belts, obtained in this study, show greater intensity in the equatorial belt than those obtained empirically by other authors (e.g. Jacobs). Palmen obtained a similar result some time ago.

Harmonic analyses show that in the equatorial belt proper, no definite wave number can be ascribed to the eddy vapour transport. In the subtropics, wave numbers one and two appear to be the active agents, whilst beyond 30° N wave numbers four and six take over.