Stationary Rossby Waves in Southern Winter

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This set of figures shows the structure and evolution of stationary Rossby waves at 67 deg S latitude, as observed with MGS radio occultation experiments. The season is winter in the southern hemisphere (Ls = 135-160 deg). The data have been filtered to isolate structure that is stationary with respect to the surface at zonal wave number 1 (i.e., 1 cycle per 360 deg of longitude). The results are displayed as departures from the zonal average. The figures show longitude-pressure cross sections of (left) geopotential height in meters and (right) temperature in kelvin at four time steps (Ls = 140, 145, 150, and 155). The contour intervals are 50 m and 1 K; shading denotes negative values. This range of pressures corresponds to altitudes of 1-30 km above the surface.

Stationary Rossby waves are excited by atmospheric flow across large-scale zonal variations in surface topography. Their behavior is extremely sensitive to seasonal changes in the zonal circulation. In the measurements shown here the wave amplitude generally increases with time. For example, the amplitude in geopotential height at 100 Pa (1 mb) increases from 120 m at Ls = 140 to 280 m at Ls = 155, while the amplitude in temperature at 300 Pa increases from 1 K at Ls=140 to 3 K at Ls = 155. Near the surface, the meridional winds implied by the geopotential field are poleward near 120 deg E longitude and equatorward near 300 deg E. The resulting circulation produces poleward advection of warm air and equatorward advection of cold air.

Last updated: May 31, 2001
Dave Hinson / Joe Twicken