中高纬度Rossby波活动对华南前汛期EAP事件中期演变过程的影响

文中从中期过程的角度探讨了Rossby波活动在华南前汛期东亚-太平洋遥相关型事件的形成、成熟和衰减过程中的作用，并得出如下结果：（1）正负东亚-太平洋遥相关型事件的形成过程有相似之处：在对流层中上层，源自东北大西洋或欧洲的Rossby波在欧亚大陆中高纬弱波导区中不断地向下游频散，最终在东亚地区形成东亚-太平洋遥相关型事件的3个异常中心。在东亚-太平洋遥相关型事件的3个异常中心之间，Rossby波能量从高纬度向中纬度和副热带地区频散。东亚 太平洋遥相关型事件副热带异常中心的形成归因于东亚副热带急流波导的存在以及上游中高纬度地区Rossby波能量的注入。在对流层低层，Rossby波则从亚洲副热带地区向东亚中纬度地区频散。（2）东亚-太平洋遥相关型事件的3个异常中心在对流层中上层中，西太平洋副热带地区异常中心最后形成。（3）正负东亚-太平洋遥相关型事件也并不是简单的反位相演变过程：在对流层中上层，在正事件成熟阶段，斯堪的纳维亚半岛上的正异常环流基本维持了其中心强度和位置，它不断地向下游东亚地区频散能量，使正事件的持续时间较长；在负事件中，由于中高纬度盛行纬向型环流，波能量的频散较快，因而负事件成熟阶段的持续时间比正事件短。（4）在这一时期，东亚-太平洋遥相关型事件对中国长江以南地区的降水形势具有显著的影响。正（负）东亚-太平洋遥相关型事件易引起长江以南降水异常偏多（少）。

The impact of mid-and high-latitude Rossby wave activities on the medium range evolution of EAP event in the pre-rainy period of South China.

Based on the NCEP-DOE AMIP-Ⅱ daily reanalysis data (1979-2005), the evolution of the EAP event during the pre-rainy period of South China is studied on the medium range time scale. It is shown that: (1) The life cycles of positive and negative EAP events share some similarities: in the middle and upper troposphere, Rossby wave packets emanating from the northeast Atlantic or Europe propagate toward East Asia along the Eurasian continent waveguide and finally give rise to the three anomaly centers of EAP event over East Asia. Among the three anomaly centers, Rossby wave packets propagate from the high-latitude anomaly center toward the middle-latitude and subtropical ones. The enhancement and maintenance of the subtropical anomaly center is closely associated with the existence of subtropical jet waveguide and with the incoming of Rossby wave packets from the upstream. In the lower troposphere, Rossby wave packets emanating from Asia subtropical area toward East Asia. (2) Among the three anomaly centers of EAP events in the middle and upper troposphere, the western Pacific subtropical one appears latter most. (3) Yet, the positive and negative EAP events could not be regarded as “mirror” each other. For the positive event, the positive height anomaly center around the Scandinavia Peninsula keep its strength and position during the mature period, and the Rossby wave packets thus propagate persistently toward East Asia, facilitating a longer ripe time of the positive event. As for the formation of negative EAP event, however, the incoming Rossby wave energy from the upstream contribute to both the enhancement and southeastward movement of the negative anomaly belt from the Yenisei River to the Bering Strait and the positive anomaly center around Mongolia. At the peak time, those two anomaly circulations become the northeast Asia and middle-latitude anomaly centers of the negative event, respectively. The energy dispersion of Rossby wave packets is relatively fast due to the predominant zonal circulation in the extratropics, causing a shorter mature period of the negative event. (4) During the pre-rainy period of South China, the prevalence of the EAP event significantly affects the rainfall over the region south of the Yangtze River. The positive (negative) EAP event tends to cause the positive (negative) precipitation anomalies of the region south of the Yangtze River, which is different from the early research based on the monthly mean data.