Estimates of atmospheric angular momentum friction, and mountain torques during 1987-1988

Abstract

Atmospheric angular momentum (M), friction (TF), and mountain torques (TM) are estimated from a 13-month period of European Center for Medium-Range Weather Forecasts (ECMWF) data. Cross-spectrum analysis between M and total torques results in high coherence and one-quarter cycle phase angles (TF + TM leading M) for timescales between 5 and 66 days, suggesting that variations of the total torque are reasonably well estimated for these slower variations. During the period there are few near 50-day oscillations in the M. Two oscillations in M that are coincident with eastward-propagating cloud complexes of tropical intraseasonal oscillations are examined more closely. It is found that TF and TM work together to alter the M on the 50-day timescale, but that TM's contribution is three times larger than that of TF. -from Authors