Seasonal Variation of the Global Water Balance Based on Aerological Data

The distribution of evaporation minus precipitation over the globe and its seasonal variations are estimated from global atmospheric circulation statistics for the period May 1963 to April 1973. Meridional profiles of evaporation minus precipitation over the Atlantic, Pacific, and Indian oceans, over all oceans combined, and over all continents combined, as well as the total evaporation minus precipitation over each oceanic and continental region, are shown. The Pacific Ocean is found to have an excess of precipitation and the Atlantic an excess of evaporation throughout he year. Over the Indian Ocean, precipitation exceeds evaporation during December-February, while evaporation exceeds precipitation during the rest of the year and in the annual mean. The results are generally in qualitative agreement with previous estimates of the annual mean world water balance based on surface observations. There are large quantitative discrepancies, however, particularly in the subtropics. A comparison with the analysis of 2 months of data from the FGGE period suggests that the primary source of error in our results is associated with spatial sampling deficiencies in the general circulation statistics. It appears that in many regions the current operational rawinsonde network is inadequate to give reliable quantitative estimates of differentiated quantities such as are required in computing the atmospheric water balance.