Quasi-stationary wave variability in NSCAT winds

Planetary and interseasonal properties of the NASA scatterometer (NSCAT) wi nds are explored in the context of the quasi-stationary waves (QSWs) of the southern hemisphere. The QSWs are examined by means of zonal asymmetries o f 3-month running averages of the meridional velocity derived from NSCAT. T he study period spans the entire NSCAT record from September 15, 1996, thro ugh June 29, 1997, Meridional winds from the European Space Agency ERS 2 sc atterometer are used to augment 3-month averages centered on August 1996 th rough May 1997. The time period corresponds to the transition from year -1 to 0 of the 1997 warm event in the Southern Oscillation. Comparisons are ma de with QSW signals in geopotential height anomalies from the National Cent ers for Environmental Prediction/National Center for Atmospheric Research C limate Data Assimilation System. The zonal anomalies of meridional wind fro m NSCAT are shown to be in approximate geostrophic balance with zonal gradi ents in the zonal anomalies of geopotential height at 500 and 1000 hPa.