Numerical Experiments with Large-Scale Seasonal Forcing

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Abstract

Experiments with six different heating fields in a numerical general circulation model are described. Three different vertical heating gradients are each used once with and once without variations on the continental-oceanic scale along parallel circles. The zonal and the meridional heating fields are forced to vary seasonally. Integration has been carried out over a simulated period of one century for one particular configuration, and over periods of five years for each of the five other configurations. Results which may be represented by an electrical analogue are rather similar to actual general circulation observations. They also show stronger summer westerlies and North-South temperature gradients in the model without schematic oceans and continents. Dynamic lag effects cause differences between the “climates” of spring and fall. In all experiments there was a breakdown in fall of a predominantly zonal circulation, accompanied by the development of “equinoctial storms.” Lag correlations computed for the mean zonal thermal wind in the 100-year experiment show persistence in summer between successive ten-day means and significant negative values over longer lag periods. No significant lag correlations were found during the winter months.

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