The Influence of the Tropics on the Prediction of Ultralong Waves. Part II: Latent Heating

Abstract

The influence of tropical latent heating on the short-to-medium-range numerical prediction of ultralong waves is examined. Two integrations of the GLAS general circulation model are made from the came initial state. One forecast utilizes the full model physics, the other contains no latent heating in the tropical belt from 20°S to 20°N. The tropical and subtropical divergence fields react to differences in the latent heating within half a day. Differences in the rotational wind field within these latitudes are noted in about three days, while at mid-latitudes (30°?60°) the influence is not felt until five days. At higher latitudes the five-day predictions of a strong North Atlantic block with and without latent heating are quite similar. Although the greatest changes in the heating field occur in the Southern Hemisphere, the largest temperature, height and wind change take place in the Northern Hemisphere. It appears that the upper troposheric tropical westerlies are sustained in the model by tropical heat sources, and reverse to easterlies when these sources are removed.