Quasi-stationary wave variability in NSCAT winds

Planetary and interseasonal properties of the NASA scatterometer (NSCAT) winds are explored in the context of the quasi-stationary waves (QSWs) of the southern hemisphere. The QSWs are examined by means of zonal asymmetries of 3-month running averages of the meridional velocity derived from NSCAT. The study period spans the entire NSCAT record from September 15, 1996, through June 29, 1997, Meridional winds from the European Space Agency ERS 2 scatterometer are used to augment 3-month averages centered on August 1996 through 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 made with QSW signals in geopotential height anomalies from the National Centers for Environmental Prediction/National Center for Atmospheric Research Climate Data Assimilation System. The zonal anomalies of meridional wind from NSCAT are shown to be in approximate geostrophic balance with zonal gradients in the zonal anomalies of geopotential height at 500 and 1000 hPa.