| Dynamical diagnosis of the breakup of the stratospheric polar vortex in the Northern Hemisphere |
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| 作者单位： | WEI Ke（Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080, China;Graduate University of the Chinese Academy of Sciences, Beijing 100049, China） ;
CHEN Wen（Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080, China） ;
HUANG RongHui（Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080, China） ; |
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| 摘 要： | The research on climate change in polar regions, especially on the role of polar in the global climate system, has gain unprecedented level of interest. It has been the key scientific issue of the International Polar Year program (IPY, 2007―2008). In this paper, we dealt with the debate upon the breakup time of the stratospheric polar vortex in boreal spring. An observational study of the relation between strato- spheric polar vortex breakup and the extra-tropical circulation was performed. The mean breakup date―when the winter westerly at the core of polar jet turns to summer easterly―is about April 10. The breakup time has large interannual variation with a time span of about 2 months. It also has a long-term trend with the 1990s and 2000s witnessing more and more late breakups of polar vortex. Composite of wind speed at the core of polar jet for the extremely early and late breakup years shows that late years have two periods of westerly weakening while early breakup years have only one. The first weakening in the late years happens in middle January with wind speed dropping sharply from more than 40 m s?1 to about 15 m s?1. This is accompanied with anomalous activities of planetary waves in both strato- sphere and troposphere; while the second weakening in the late breaking years is mainly the results of diabatic heating with very weak wave activities. In early breakup years, the transition from westerly to easterly is rapid with wind speed dropping from more than 30 m s?1 to less than ?10 m s?1 within a month. This evolution is associated with a strong bidirectional dynamical coupling of the stratosphere and troposphere. The circulation anomalies at low troposphere are also analyzed in the extremely early and late breakup years. It shows that there are significant differences between the two kinds of extreme years in the geopotential height and temperature composite analysis, indicating the dynamical cou- pling of stratosphere and troposphere with the evolution of stratospheric polar vortex.
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| 收稿时间： | 29 March 2007 |
| 修稿时间： | 9 May 2007 |
Dynamical diagnosis of the breakup of the stratospheric polar vortex in the Northern Hemisphere |
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| Authors: | Wei Ke Chen Wen Huang RongHui |
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| Institution: | 1. Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080, China;Graduate University of the Chinese Academy of Sciences, Beijing 100049, China
2. Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080, China |
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| Abstract: | The research on climate change in polar regions, especially on the role of polar in the global climate system, has gain unprecedented
level of interest. It has been the key scientific issue of the International Polar Year program (IPY, 2007–2008). In this
paper, we dealt with the debate upon the breakup time of the stratospheric polar vortex in boreal spring. An observational
study of the relation between stratospheric polar vortex breakup and the extra-tropical circulation was performed. The mean
breakup date—when the winter westerly at the core of polar jet turns to summer easterly—is about April 10. The breakup time
has large interannual variation with a time span of about 2 months. It also has a long-term trend with the 1990s and 2000s
witnessing more and more late breakups of polar vortex. Composite of wind speed at the core of polar jet for the extremely
early and late breakup years shows that late years have two periods of westerly weakening while early breakup years have only
one. The first weakening in the late years happens in middle January with wind speed dropping sharply from more than 40 m
s−1 to about 15 m s−1. This is accompanied with anomalous activities of planetary waves in both stratosphere and troposphere; while the second
weakening in the late breaking years is mainly the results of diabatic heating with very weak wave activities. In early breakup
years, the transition from westerly to easterly is rapid with wind speed dropping from more than 30 m s−1 to less than −10 m s−1 within a month. This evolution is associated with a strong bidirectional dynamical coupling of the stratosphere and troposphere.
The circulation anomalies at low troposphere are also analyzed in the extremely early and late breakup years. It shows that
there are significant differences between the two kinds of extreme years in the geopotential height and temperature composite
analysis, indicating the dynamical coupling of stratosphere and troposphere with the evolution of stratospheric polar vortex.
Supported by the National Natural Science Foundation of China (Grant No. 40575026) |
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| Keywords: | stratospheric polar vortex wave-flow interaction diabatic heating final breakup stratosphere-troposphere coupling |
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