UPWARD TRANSPORT OF WESTERLY MOMENTUM DUE TO DISTURBANCES OF THE EQUATORIAL LOWER STRATOSPHERE IN THE PERIOD RANGE OF ABOUT 2 DAYS - A SINGAPORE DATA-ANALYSIS FOR 1983-1993

Twice-daily time series upper-air data at Singapore (1.4 N, 104.0 E) during the years 1983-1993 are analyzed to examine disturbances in the period range of about 2 days. The covariance between the zonal wind component and the temperature change per day is found to be prevailingly negative in the 100-10 hPa layer. This indicates upward transport of the westerly momentum. The fluxes are shown to be related strongly with the QBO cycle and the largest flux occurs in the region where the westerly regime is descending. The fluxes caused by the disturbances in the period range of about 2 days are as large as those by Kelvin waves in the period range of 7.4-32 days. The disturbances behave like Kelvin waves to the extent that the disturbances are associated with the zonal wind component and temperature but no corresponding meridional component.