EARTH-ATMOSPHERE EXCHANGE OF ANGULAR-MOMENTUM SIMULATED IN A GENERAL-CIRCULATION MODEL AND IMPLICATIONS FOR THE LENGTH OF DAY

The atmospheric angular momentum budget simulated in the Canadian Climate Centre general circulation model is investigated. It is found that on time scales of days the mountain and stress torque terms contribute to the rate of change of angular momentum (and by implication the lod) in the ratio of 60-40%, while at weekly and longer time scales the stress torque dominates by increasing amounts. The notable contemporaneity of changes in the length of day and of atmospheric angular momentum suggests that much of the interaction occurs directly with the solid Earth and that the oceans, despite their large area, play a lesser role. This is verified in the simulation where the sum of the stress and mountain torque over land contributes of the order of 85-90% to the variation in angular momentum for time scales of days to months. -from Author