Spatial Variability of Sea Level Pressure and 500 mb Height Anomalies over the Southern Hemisphere

Jeffery C. Rogers Department of Geography, The Ohio State University, Columbus 43210

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Harry van Loon National Center for Atmospheric Research, Boulder, CO 80307

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Abstract

The spatial variability of mean sea level pressure (SLP) and 500 mb height anomalies over the Southern Hemisphere during summer (DJF) and winter (JJA) is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979. The patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data, and the eigenvectors are compared between the seasons and to those found for the Northern Hemisphere.

The first eigenvector shows that midlatitude anomalies of SLP and 500 mb height are of an opposite sign to those found over and around Antarctica. The pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts. The 500 mb height differences are calculated for five midlatitude to Antarctic station pairs using data from the late 1950's onward. These latitudinal height differences are also used to describe the association between the hemispheric westerlies and the Southern Oscillation. They also suggest that the summertime westerlies strengthen and weaken simultaneously around the hemisphere, whereas in winter this zonal symmetry is interrupted in the South America–Antarctic Peninsula region. In this region, wintertime variations in the westerlies are associated with the second eigenvector, and large interannual variations in the SLP and latitudinal variations in storm tracks occur over the Drake Passage. The second eigenvector is shown to be associated with the large standard deviations of winter mean temperature along the Antarctic Peninsula, to variations in sea ice duration at Laurie Island in the South Orkneys, and to the Trans-Polar Index of Pittock, which describes the tendency for the surface polar vortex to be displaced either toward Tasmania or the Falkland-South Sandwich Islands region.

It is concluded that temperature and circulation teleconnections, similar to those of the Northern Hemisphere, also occur in the Southern Hemisphere, and are associated with standing waves in the atmosphere The small amount of land south of 35°S probably accounts for the uniform variations in the westerlies across the Southern Hemisphere, whereas, in the Northern Hemisphere, variations in the westerlies shown by the eigenvectors are largely confined to the oceans.

Abstract

The spatial variability of mean sea level pressure (SLP) and 500 mb height anomalies over the Southern Hemisphere during summer (DJF) and winter (JJA) is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979. The patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data, and the eigenvectors are compared between the seasons and to those found for the Northern Hemisphere.

The first eigenvector shows that midlatitude anomalies of SLP and 500 mb height are of an opposite sign to those found over and around Antarctica. The pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts. The 500 mb height differences are calculated for five midlatitude to Antarctic station pairs using data from the late 1950's onward. These latitudinal height differences are also used to describe the association between the hemispheric westerlies and the Southern Oscillation. They also suggest that the summertime westerlies strengthen and weaken simultaneously around the hemisphere, whereas in winter this zonal symmetry is interrupted in the South America–Antarctic Peninsula region. In this region, wintertime variations in the westerlies are associated with the second eigenvector, and large interannual variations in the SLP and latitudinal variations in storm tracks occur over the Drake Passage. The second eigenvector is shown to be associated with the large standard deviations of winter mean temperature along the Antarctic Peninsula, to variations in sea ice duration at Laurie Island in the South Orkneys, and to the Trans-Polar Index of Pittock, which describes the tendency for the surface polar vortex to be displaced either toward Tasmania or the Falkland-South Sandwich Islands region.

It is concluded that temperature and circulation teleconnections, similar to those of the Northern Hemisphere, also occur in the Southern Hemisphere, and are associated with standing waves in the atmosphere The small amount of land south of 35°S probably accounts for the uniform variations in the westerlies across the Southern Hemisphere, whereas, in the Northern Hemisphere, variations in the westerlies shown by the eigenvectors are largely confined to the oceans.

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