摘要:本文利用ECMWF再分析资料及Hadley中心提供的海温数据分析了20世纪90年代以后华北地区初春低温增强的原因，并通过数值模拟结果予以验证。结果表明，北大西洋“马蹄型”海温模态与影响我国华北地区的欧亚波列存在显著的相关关系。同时该海温模态与1997年以后北大西洋关键区垂直波作用通量有着较密切的相关关系，1997年以后北大西洋地区的500 hPa环流模态，整体呈现出东移南撤的趋势。1997年以后格陵兰岛东侧表面温度受异常热力强迫导致正值区增多，同时此处西风急流加大，有利于Rossby波向下游传播，导致其下游欧洲大陆地区形成暖脊。通过局地多尺度能量涡度分析法（Localized Multiscale Energy and Vorticity Analysis，简称MS-EVA）证明格陵兰岛东侧关键区表面温度的异常热力强迫作用与气压梯度力在对流层整层做正功，导致高层动能的增加并向外辐散，使得脊加强向北伸展。通过欧亚波列致使下游华北地区上空气旋式异常加强，促使亚洲极涡加强和稳定维持，华北地区温度下降剧烈，极端低温事件增多。最后通过CAM5.1模式模拟研究了北大西洋“马蹄型”海温模态对大气环流异常及华北地区极端低温的影响。模拟结果很好地验证了观测结果，进一步表明该海温模态可以通过激发出欧亚波列，影响欧亚大陆大气环流异常，进而导致我国华北地区气旋性加强和经向环流加大，极端低温事件增多。
关键词:极端低温/
北大西洋海温/
能量分析/
CAM5.1模式
Abstract:Based on reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and sea-surface temperature (SST) data from the Hadley Center (Hadley), in this paper, we present our analyses and determination of the reason for the extreme low-temperature events of the North China’s enhancement in spring since the 1990s, which we verified by numerical simulation. The results indicate a significant correlation between the North Atlantic “Horse Hoof” SST mode and the Eurasian (EU) wave train, which could be a factor in North China’s extreme low-temperature events. The SST mode was also found to be closely correlated with the vertical wave energy in key areas of the North Atlantic after 1997. The 500-hPa circulation mode in the North Atlantic for the same period showed a trend of eastward movement and southward withdrawal. Since 1997, the expansion of the regional scope of positive surface temperature forced by thermal anomalies adjacent to eastern Greenland, as well as increases in the westerly jet stream, could have stimulated the EU pattern and generated warm ridges downstream of the Eurasian continent. The results obtained using the localized multiscale energy and vorticity analysis (MS-EVA) method revealed that the forces of the surface thermal anomalies and the pressure gradient in the key area of eastern Greenland have had a positive effect on the whole troposphere, which have led to an increase and divergence of high-level kinetic energy and a strengthening of the ridge toward the north. Via the EU wave train, the cyclonic anomaly was strengthened downstream from North China, and the Asian polar vortex was both strengthened and maintained. The temperature in North China decreased sharply, which increased the number of extreme low-temperature events. Finally, we used the CAM5.1 model to simulate the effects of the North Atlantic “Horse Hoof” SST mode on the atmospheric circulation anomalies and the extreme low temperatures in North China. We found the simulation results to agree well with the observation results. This further confirms that the SST mode can affect the atmospheric circulation anomalies in Eurasia by stimulating the EU wave train, thereby leading to the intensification of cyclones and meridional circulation, as well as increasing the number of extreme low-temperature events in North China.
Key words:Extreme low temperature/
North Atlantic sea surface temperature/
Energy analysis/
Community Atmosphere Model (CAM5.1)
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