On the Role of the Tropics in the General Circulation of the Atmosphere

Contrary to older descriptions, the air currents in the middle and upper troposphere over the low latitudes are not steady but highly variable. There are trains of well-developed waves or vortices. When these disturbances combine with troughs in the polar westerlies, the resulting extended troughs often reach from pole to equator. Poleward flow of heat must take place mainly along these troughs. Energy from low latitudes is injected into the temperate zone in narrow and variable areas only.

A description of the tropical atmosphere in the layers below and above the bases of the cumuli leads to an attempt to explain the steadiness of the low-level wind field which contrasts with the high variability of the upper layers. Then the strength of the mean meridional circulation and the fields of divergence and convergence at the surface are calculated, followed by a summary of available information on the high-level circulation. The field of motion aloft varies greatly with longitude, so that inferences concerning the tropics as a whole can only be made from maps covering most longitudes. Such maps (300-mb charts) are available for a limited period down to latitude 10° N. They indicate that regions where the easterlies decrease upward alternate with regions of increasing easterlies.