冬季东亚高空急流季节内协同变化及对我国东部降水的影响

INTRA-SEASONAL CONCURRENT VARIATION OF THE EAST ASIAN UPPERJET STREAM IN WINTER AND ITS INFLUENCE ON PRECIPITATIONIN EAST CHINA

关键词:  副热带急流  温带急流  协同变化  季节内振荡  东部降水

Key words:  East Asian subtropical jet  East Asian polar-front jet  concurrent variation  intra-seasonal oscillation  precipitation in East China

摘要:

利用ERA-Interim再分析资料，采用滤波和合成分析等统计方法，分析了冬季东亚高空急流的季节内协同变化以及对我国东部降水的影响，结果表明：在季节内尺度(10～90天)中，东亚地区冬季300 hPa逐日纬向风主要表现为准双周振荡(10～30天)。300 hPa低频纬向风异常整体向东传播，高纬的低频纬向风异常向南传播，低纬低频纬向风没有明显经向传播特征。伴随低频纬向西风从里海附近开始向东移动至西北太平洋上空，温带急流向东再向东南移动并且强度先增强再减弱，副热带急流位置没有明显变化，强度演变特征与温带急流变化相反。降水异常对300 hPa风场低频振荡有显著响应，低频降水主要出现在我国东部，随时间向东移动，移至西太平洋附近消失；受低频风场影响，温带急流偏强，副热带急流偏弱时，我国东部高空辐合，地面表现为低频高压，整层有较强下沉气流，地面为东北风控制，不易产生降水；温带急流偏弱，副热带急流偏强时，青藏高原北侧整层一致东风异常，南侧整层一致西风异常，使我国东部高空辐散，地面受低频低压控制，我国东部产生整层上升运动，并且有西南风水汽输送，水汽辐合，我国东部出现低频降水正异常。

Abstract:

Based on the ERA-Interim reanalys is data, the paper analyzed the intra-seasonal concurrent variation of the East Asian upper jet stream in winter and its effects on precipitation in East China. The results show that the zonal wind at 300 hPa over East Asia in winter has significant intra-seasonal differences in oscillation intensity, and the dominant period is 10～30 day. The anomalous low-frequency zonal wind propagates eastward as a whole, and the low-frequency zonal wind at high latitudes propagates southward, while the low-frequency zonal wind at low latitudes has no significant meridional propagation. As the low-frequency zonal wind moves from the Caspian Sea to the Northwest Pacific Ocean, the East Asian polar-front jet (EAPJ) moves eastward and then southeastward, and its intensity increases first and then weakens. While the position of the East Asian subtropical jet (EASJ) does not change significantly, its intensity variation is opposite to that of the EAPJ. The precipitation anomaly has a significant response to the low-frequency oscillation of the 300 hPa zonal wind. Low-frequency precipitation mainly occurs in the eastern part of China, moves eastward with time, and disappears near the western Pacific Ocean. Under the influence of low-frequency zonal wind, the EAPJ is stronger and the EASJ is weaker. When the high-altitude convergence occurs in the eastern part of China, low-frequency high pressure dominates the ground, and there is strong downdraft in the whole 300 hPa layer. The ground is controlled by northeast wind, and it is not easy to generate precipitation. When the polar-front jet stream is weaker and the subtropical jet stream is stronger, east wind anomaly occurs in the whole 300 hPa layer on the north side of the Tibet Plateau, and west wind anomaly occurs in the whole 300 hPa layer on the south side of the Tibet Plateau. The upper air in the east of China diverges, and the ground is controlled by low-frequency low pressure. As a result, the whole 300 hPa layer in the east of China rises, there is water vapor transported by southwest wind and water vapor convergence, and the positive anomaly of low-frequency precipitation appears in the east of China.