An Analysis of Climatological Patterns of the Northern Hemispheric Circulation

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  • 1 Climatic Analysis Center, National Meteorological Center, National Weather Service/NOAA, Washington, DC 20233
  • | 2 Department of Atmospheric Science, University of Missouri, Columbia, MO 65211
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Abstract

Eigenvector and harmonic analyses have been performed with monthly mean values of upper air parameters of the Northern Hemispheric circulation for the period from April 1955 to December 1974. The parameters used involve the 700 and 500 mb temperatures, the 700–500 mb thickness, the 300 mb kinetic and eddy kinetic energies, and the 700, 500 and 300 mb zonal/meridional flow indicators. The zonal/meridional flow indicator is defined as the ratio |u|/|v|, where the bar indicates the monthly mean.

The first eigenvectors of the normalized parameters are associated with the annual variation of the basic patterns. For the temperature field the first eigenvector overwhelmingly dominates. It reflects the annual variation of temperature in the mid and higher latitudes with an effect of the land-ocean configuration. The second eigenvector shows a land-ocean contrast. The long-term variation of temperature in the lower latitudes also stands out. For the kinetic energy and zonal/meridional flow indicator the first eigenvectors are not as dominant as that of temperature. They reflect the subtropical jet and other hemispherical-scale circulations. The third eigenvector of kinetic energy and second eigenvector of the zonal/meridional flow indicator appear to be associated with the semiannual oscillations of the large-scale wind systems including summer and winter monsoons. It also appears that high-numbered eigenvectors of kinetic energy and zonal/meridional flow indicators are associated with long-term variations in the lower latitudes and short-term variations in the mid to high latitudes.

Abstract

Eigenvector and harmonic analyses have been performed with monthly mean values of upper air parameters of the Northern Hemispheric circulation for the period from April 1955 to December 1974. The parameters used involve the 700 and 500 mb temperatures, the 700–500 mb thickness, the 300 mb kinetic and eddy kinetic energies, and the 700, 500 and 300 mb zonal/meridional flow indicators. The zonal/meridional flow indicator is defined as the ratio |u|/|v|, where the bar indicates the monthly mean.

The first eigenvectors of the normalized parameters are associated with the annual variation of the basic patterns. For the temperature field the first eigenvector overwhelmingly dominates. It reflects the annual variation of temperature in the mid and higher latitudes with an effect of the land-ocean configuration. The second eigenvector shows a land-ocean contrast. The long-term variation of temperature in the lower latitudes also stands out. For the kinetic energy and zonal/meridional flow indicator the first eigenvectors are not as dominant as that of temperature. They reflect the subtropical jet and other hemispherical-scale circulations. The third eigenvector of kinetic energy and second eigenvector of the zonal/meridional flow indicator appear to be associated with the semiannual oscillations of the large-scale wind systems including summer and winter monsoons. It also appears that high-numbered eigenvectors of kinetic energy and zonal/meridional flow indicators are associated with long-term variations in the lower latitudes and short-term variations in the mid to high latitudes.

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