OBSERVATIONAL STUDIES OF GENERAL CIRCULATION OF TROPICS - LONG TERM MEAN VALUES

Data from 298 stations between 45°N and 30°S have been processed for the period July 1957 to December 1964. The mean wind and temperature fields are presented together with the momentum and heat fluxes for two three month seasons, December‐February and June‐August. The tropospheric results were obtained from objective analysis of the long term station means and the stratospheric results from latitude band means giving equal weight to data from odd and even years so that the biennial component has been virtually eliminated. The mean temperature cross‐sections show little seasonal variation in the tropical troposphere and gradients are small. The maximum temperature is in the vicinity of 5°S during the southern summer but moves to 20°N during June‐August as a consequence of stronger heating over the continents. In the tropical stratosphere the seasonal variation is from lower temperatures in December‐February to higher temperatures in June‐August. The mean zonal wind pattern shows the tropical easterlies to be stronger and to occupy a greater range of latitudes in the upper troposphere during June‐August. The Hadley circulation obtained appears quite reasonable with the winter hemisphere cell predominating and extending over the Equator. Although all three components of the momentum flux were evaluated for the troposphere, only the transient eddy contribution could be obtained for the stratosphere. A strong flux is observed in the upper equatorial troposphere directed into the summer hemisphere. The sensible heat‐flux in the middle troposphere is equatorward in the Tropics of both hemispheres and a small transport into the summer hemisphere is noted. This equatorward flux is countergradient in both hemispheres except during the northern summer. The mean motion transport of total energy is about an order of magnitude larger than the eddy transport at the Equator and supplies energy to the winter hemisphere. The zonal and eddy forms of kinetic energy and available potential energy have been evaluated for the tropical troposphere together with all conversions between them except for that by transient eddies between available potential energy and kinetic energy. On the average, kinetic energy contents are about twice as large as available potential energy contents and the momentum flux conversions are larger than those involving heat fluxes. The conversion by the mean motions, however, is largest of all over the range 24°N‐24°S and leads to a rejuvenation time of some 3–5 days for the zonal kinetic energy. This conversion appears to be sufficiently large to offset the destruction in middle latitudes. Taken together, the results presented here give a consistent pattern for the tropical circulation. The direct Hadley cell is seen as a source of both heat and momentum which are distributed by the eddy fluxes. The energy supply for the mean cell is thought to be the latent heat of condensation in its ascending branch. Copyright © 1969 Royal Meteorological Society