ANGULAR-MOMENTUM AND TORQUES IN A SIMULATION OF THE ATMOSPHERES RESPONSE TO THE 1982-83 EL-NINO

Anomalies in the angular momentum of the atmosphere (M) during the 198 2-83 El Nino event and the torques responsible for these anomalies are investigated using output from the Canadian Climate Centre general ci rculation model. Model values of M during the year of the event are ge nerally larger than those for the model climatology, thereby capturing the observed tendency toward higher values of M during El Nino. Diffe rences exist between the model and observations in the timing and ampl itude of the largest anomalies, but these differences may be due to na tural variability and not necessarily directly associated with the 198 2-83 El Nino conditions. In late September and October 1982, the model atmosphere acquires momentum more rapidly than usual, leading to the development of the largest deviations from mean conditions at the end of this period, mostly associated with strong westerly momentum signal s centered at 25-degrees-N. Large, sustained positive anomalies in tan gential stress torques over the northern tropics are the major mechani sm responsible for the modeled increase in M, but mountain torque anom alies centered at 35-degrees-N are also important at the end of Octobe r. A secondary maximum in the departure from mean M values occurs in J anuary 1983 and is related to a general strengthening of westerly mome ntum anomalies over the model's tropical and midlatitude regions. Both mountain and tangential stress torques are involved in this episode, but no particular mechanism or region dominates the anomalous exchange of momentum.