Rossby Wave Propagation and Teleconnection Patterns in the Austral Winter

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  • 1 Department of Meteorology, University of Reading, Reading, United Kingdom
  • | 2 Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan
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Abstract

Observational evidence of and theoretical support for the Northern and Southern Hemisphere teleconnection patterns in the austral (Southern Hemisphere) winter are examined through an upper troposphere streamfunction teleconnectivity map and time-lag cross-correlation analysis using ECMWF initialized analysis 2OO-hPa winds for the 11 June–August periods from 1979 to 1989.

As was previously found for the Northern Hemisphere winter, the regions of strong teleconnectivity, particularly in the winter hemisphere, tend to he oriented in the zonal direction and coincide with the location of the major jet streams. Although equatorward propagation from the Northern and Southern Hemispheres is observed, little evidence of cross-equatorial propagation has been found.

For comparison, the response of a barotropic model, linearized about a climatological 300-hPa June–August time-mean flow to localized forcing is determined. It is found that the activity tends to be trapped inside each of the Southern Hemisphere subtropical and polar jet streams, with these acting as waveguides. In the Northern Hemisphere a weak waveguide belt is found near 40°N around the whole hemisphere. The patterns simulated by the model are generally in good agreement with the teleconnectivity study described above. Both the observations and the model support the existence of the Pacific–South American pattern.

Abstract

Observational evidence of and theoretical support for the Northern and Southern Hemisphere teleconnection patterns in the austral (Southern Hemisphere) winter are examined through an upper troposphere streamfunction teleconnectivity map and time-lag cross-correlation analysis using ECMWF initialized analysis 2OO-hPa winds for the 11 June–August periods from 1979 to 1989.

As was previously found for the Northern Hemisphere winter, the regions of strong teleconnectivity, particularly in the winter hemisphere, tend to he oriented in the zonal direction and coincide with the location of the major jet streams. Although equatorward propagation from the Northern and Southern Hemispheres is observed, little evidence of cross-equatorial propagation has been found.

For comparison, the response of a barotropic model, linearized about a climatological 300-hPa June–August time-mean flow to localized forcing is determined. It is found that the activity tends to be trapped inside each of the Southern Hemisphere subtropical and polar jet streams, with these acting as waveguides. In the Northern Hemisphere a weak waveguide belt is found near 40°N around the whole hemisphere. The patterns simulated by the model are generally in good agreement with the teleconnectivity study described above. Both the observations and the model support the existence of the Pacific–South American pattern.

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