Temperate Latitude 200-mb Zonal Winds from GHOST Balloon Flights in the Southern Hemisphere

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  • 1 National Center for Atmosphere Research, Boulder, Colo.
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Abstract

Constant level balloon (GHOST) flights at 200 mb in the temperate latitudes of the Southern Hemisphere provide an estimate of zonal wind as a function of latitude and month. In the mean for the year, at this surface, the west wind is nearly half again as strong in the Southern Hemisphere as in the Northern. In the Southern Hemisphere both a polar front jet, of magnitude 29 m sec−1 at 45S, and a subtropical jet of magnitude 35 m sec−1 at 20S, are distinguished in the yearly average. This tendency for a double jet at 200 mb is most pronounced in the Southern Hemisphere spring and summer, and presumably is related, through the thermal wind equation, to snow-covered Antarctica. Maximum mean-monthly zonal winds, of magnitude 45 m sec−1, occur at 20S during July, August and September.

A striking feature of the 200-mb zonal flow in the Southern Hemisphere is the magnitude of the semi-annual oscillation. This oscillation has an amplitude exceeding 4 m sec−1 at latitudes 55 and 65S and 2 m sec−1 at latitudes 25 and 35S. There is a phase shift at 45S, with the west wind maxima occurring near the time of the solstices in lower latitudes and near the time of the equinoxes in higher latitudes. In the Southern Hemisphere this semi-annual oscillation is comparable in magnitude to the annual oscillation, which is less pronounced in the Southern than in the Northern Hemisphere.

Abstract

Constant level balloon (GHOST) flights at 200 mb in the temperate latitudes of the Southern Hemisphere provide an estimate of zonal wind as a function of latitude and month. In the mean for the year, at this surface, the west wind is nearly half again as strong in the Southern Hemisphere as in the Northern. In the Southern Hemisphere both a polar front jet, of magnitude 29 m sec−1 at 45S, and a subtropical jet of magnitude 35 m sec−1 at 20S, are distinguished in the yearly average. This tendency for a double jet at 200 mb is most pronounced in the Southern Hemisphere spring and summer, and presumably is related, through the thermal wind equation, to snow-covered Antarctica. Maximum mean-monthly zonal winds, of magnitude 45 m sec−1, occur at 20S during July, August and September.

A striking feature of the 200-mb zonal flow in the Southern Hemisphere is the magnitude of the semi-annual oscillation. This oscillation has an amplitude exceeding 4 m sec−1 at latitudes 55 and 65S and 2 m sec−1 at latitudes 25 and 35S. There is a phase shift at 45S, with the west wind maxima occurring near the time of the solstices in lower latitudes and near the time of the equinoxes in higher latitudes. In the Southern Hemisphere this semi-annual oscillation is comparable in magnitude to the annual oscillation, which is less pronounced in the Southern than in the Northern Hemisphere.

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