INTRA-SEASONAL CONCURRENT VARIATION OF THE EAST ASIAN UPPER JET STREAM IN WINTER AND ITS INFLUENCE ON PRECIPITATION IN EAST CHINA
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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.
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图 1 冬季300 hPa纬向风分布(黄色等值线；单位：m/s)与纬向风标准差分布(蓝色等值线；单位：m/s)以及急流核分布(填色；单位：个)
红色实线为青藏高原所在大致区域。
图 4 东亚冬季关键区低频纬向风的EOF第一模态时间系数的超前滞后合成(a)和冬季300 hPa低频纬向风场(填色；单位：m/s；打点区域表示通过95%信度检验)与原始纬向风场(黑色细实线；单位：m/s)从-6天至6天的演变(b~h，间隔2天)
原始纬向风风速等于30 m/s(黑色粗实线)；温带急流轴(绿色实线)。
图 5 冬季300 hPa纬向风场时间-经度剖面图(a，45~60 °N区域平均；b，22~35 °N区域平均)和纬度-时间剖面图(c，70~100 °E区域平均)的超前滞后合成
单位：m/s；实线代表正值，虚线代表负值，阴影区域表示通过95%信度检验。
图 7 我国东部区域平均降水和300 hPa低频纬向风速的超前滞后合成(a，黑色：降水平均值，单位：mm/d；蓝色：温带急流区域，红色：副热带急流区域，单位：m/s)与不同时期低频降水合成(b，-3天至-1天；c，+4天至+6天；单位：mm/d；打点区域表示通过95%信度检验)
图 8 冬季不同时期300 hPa低频散度(填色；单位：10-6 s-1；打点区域表示通过95%信度检验)与低频海平面气压合成(等值线；单位：hPa；红色实线表示低频海平面气压大于0，蓝色虚线表示低频海平面气压小于0)
a.-3天至-1天；b. +4天至+6天。
图 9 冬季不同时期110~120 °E低频垂直速度(a、b；单位：Pa/s；实线表示低频垂直速度大于等于0，虚线表示低频垂直速度小于0)和70~100 °E低频纬向风(c、d；单位：m/s；等值线表示纬向风场大于等于30 m/s；黑色阴影为青藏高原区域)对低频降水事件高度-经度剖面图合成(其中a、c为-3天至-1天；b、d为+4天至+6天)
图 10 冬季不同时期850 hPa低频水汽通量(矢量；单位：kg/(m∙s∙hPa))与低频水汽通量散度(填色；单位：10-6 kg/(m2∙s∙hPa))合成
a.-3天至-1天；b. +4天至+6天。
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