学术论文

      冬季北大西洋风暴轴异常对我国寒潮活动的可能影响

      Possible Influence of the Variation of the Northern Atlantic Storm Track on the Activity of Cold Waves in China during Winter

      摘要:
      基于1961~2011年国家气象信息中心整编的566站逐日平均温度资料以及NCEP/NCAR(美国环境预报中心和国家大气研究中心)的逐日再分析资料等,利用奇异值分解(SVD)等方法,首先分析了年际尺度上冬季北大西洋风暴轴与同期我国寒潮频次的联系。发现,北大西洋风暴轴位置异常与我国寒潮频次变化存在显著的相关关系,即当在40°W以西风暴轴较气候平均位置偏北(偏南)和在40°W以东风暴轴较气候平均位置偏东北(偏西南)时,同期我国大部分地区的寒潮频次异常偏少(偏多),而其强度异常与我国寒潮频次变化的年际关系并不显著。进一步的分析结果表明,风暴轴位置的改变会引起天气尺度瞬变涡动的传播出现异常,而这种传播异常既可以直接影响我国寒潮活动,也可以通过其反馈作用影响大气环流来间接影响我国的寒潮活动。具体的可能影响过程如下:当风暴轴偏东北(偏西南)时,其离亚洲西风急流的位置较远(较近),不利(有利)于将北大西洋上强的瞬变涡动通过亚洲西风急流波导直接传播到我国地区;此时,北大西洋西风急流偏北(偏南),相应地北大西洋涛动(NAO)出现正(负)位相异常,而传播到下游的瞬变涡动通过动力反馈作用,可使得高纬西风加速(减速),极涡加深收缩(减弱扩张),冷空气禁锢在极地不易(容易)南下,而中纬西风则减速(加速),经向环流加强(减弱),从而引起西伯利亚低层冷堆温度增高(降低);最后,所有上述环流异常形势以及瞬变波的异常传播可最终导致我国的寒潮活动频次减少(增多)。
      Abstract:
      AbstractOn the basis of daily mean temperature data from 566 National Meteorological Information Center stations and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data during 1961–2011, an investigation was conducted into the relationship between the variation of the winter North Atlantic Storm Track (NAST) and the frequency of cold waves in China on the annual timescale. The results from singular value decomposition analysis show that, on the annual timescale, the position of the NAST is closely linked to the cold wave frequency in winter: When the NAST moves northeastward (southwestward), the cold wave frequency at most stations decreases (increases) significantly, but the correlation between the intensity of the NAST and the cold wave frequency is low. Further analysis indicates that change in the NAST position may lead to anomalous propagation of the Synoptic-Scale Transient Eddy Activity (STEA). This could not only affect the cold air activity of China directly, but, after first having an impact on the general circulation via feedback, it could also have an indirect influence. The possible mechanism of influence is as follows: As the NAST shifts more northeastward (southwestward), it is far from (close to) the Asian westerly jet, which is unfavorable (favorable) for the direct propagation of strong STEA over the North Atlantic region via this westerly waveguide all the way to China. Meanwhile, the North American westerly jet shifts more northward (southward) and the index of the North Atlantic Oscillation is in its positive (negative) phase. Via propagation, the downstream STEA could cause the divergence (convergence) of horizontal Eliassen-Palm fluxes over high latitudes and the convergence (divergence) over mid-latitudes, which in turn will cause acceleration (deceleration) of the westerly over high latitudes and deceleration (acceleration) of the westerly over mid-latitudes. As a result, the polar vortex will (will not) be confined to the polar region so that the cold air will uneasily (easily) move southward, and then the temperature of the low-level cold mass over the Siberian high will increase (decrease). All of the above anomalies occurring in the circulation and propagation of STEA may ultimately contribute to the reduction (enhancement) of the cold wave frequency at most stations in China.
      Author: ZHOU Xingyan ZHU Weijun GU Cong
      作者单位: 南京信息工程大学气象灾害教育部重点实验室,南京,210044
      刊 名: 大气科学 ISTICPKU
      年,卷(期): 2015, (5)
      分类号: P461
      机标分类号: P4 P42
      在线出版日期: 2015年9月23日
      基金项目: 国家自然科学基金项目41575070、41075070,公益性行业(气象)科研专项GYHY201306028,江苏高校优势学科建设工程资助项目 PAPD