ISSN 1006-9895

CN 11-1768/O4

A Comparative Analysis of Planetary Wave Activities for the 2007/2008 Strong Polar Vortex and the 2008/2009 Weak Polar Vortex
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    Abstract:

    Based on the zonal harmonic analysis of daily meteorological data, we compared and discussed the variation characteristics of the planetary wave for different wavenumbers in the stratosphere and troposphere during the strong polar vortex period in the winter of 2007/2008 and the weak polar vortex period in the winter of 2008/2009.We particularly focused on the amplitude and phase variation of the planetary wave for wavenumber-1 and wavenumber-2 along 60°N and 30°N, as well as the different 500-hPa geopotential height fields after the occurrence of the strong polar vortex and the weak polar vortex.Furthermore we discuss the reason for the different stratospheric polar vortex anomalies and the different effects on the weather and climate in eastern Asia.Finally, we investigated why this stratospheric polar vortex anomaly would cause different variations in south and north China surface temperatures.Our results show that following the stratospheric polar vortex anomaly, the planetary wave activities in the stratosphere clearly changed.The downward propagation of the abnormal polar vortex caused amplitude and phase variations in the tropospheric planetary wave and these variations are different along different latitudes.It appears that the planetary wave perturbations for wavenumber-1 and wavenumber-2 in the 500-hPa fields extended southward after the strongest polar vortex in January 2008.During and after the weakest polar vortex in January 2009, however, the planetary wave perturbations for wavenumber-1 and wavenumber-2 in the 500-hPa fields are located on the northern side.In the troposphere, the amplitude of the planetary wave is different for wavenumber-1 or wavenumber-2 and their phases are also clearly changed after the strong and weak polar vortex.These phase difference change especially with latitude.For the same year (that is say, for the same strong polar vortex in 2008 or same weak polar vortex in 2009), the planetary wave phase near 60°N is almost opposite to that near 30°N regardless of wavenumber, and cause large differences in the 500-hPa geopotential height field.Specifically, the strength and location of the Ural high pressure and the East Asia trough are different in the Eastern Hemisphere.After the strong polar vortex in January 2008, the Ural high pressure and East Asia trough extend eastward and this results in cold air not being transported to northern Eurasia (including northern China).As a result, the temperature of these areas increases.During the weak polar vortex in January 2009, the East Asia trough draws westward and this causes cold air transport to northern Eurasia, hence the temperature of these areas decreases.For the same stratospheric polar vortex anomaly (such as the strong polar vortex in 2008 or weak polar vortex in 2009), since the phase of the planetary wave disturbance in south and north China is different, the transportation of cold air to south and north China are different.Therefore, the same stratospheric polar vortex anomaly would have different effects on surface temperature in South and North China.

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History
  • Received:February 10,2014
  • Revised:May 26,2014
  • Adopted:
  • Online: March 12,2015
  • Published: