Medium-Range Numerical Forecasts of Atmospheric Angular Momentum

Abstract

Forecasts of zonal wind fields produced by the medium-range forecast (MRF) model of the National Meteorological Center are used to create predictions of the atmosphere's angular momentum at lead times of 1?10 days. Forecasts of this globally integrated quantity are of interest to geodesists and others concerned with monitoring changes in the earth's orientation for navigational purposes. Based on momentum forecasts archived for the period December 1985?November 1986, we find that, on average, the MRF exhibits positive skill relative to persistence-based forecasts at all lead times. Over our entire one-year study period, the improvement over persistence exceeds 20% for 2?6-day forecasts and remains as large as 10% even for 10-day forecasts. On the other hand, skill scores for the MRF momentum predictions vary considerably from month to month, and for a sizeable fraction of our study period the MRF is less skillful than persistence. Thus, although our initial impression of the overall quality of the MRF momentum forecasts is favorable, further improvement is certainly desirable.