ISSN 1006-9895

CN 11-1768/O4

Classification of the subseasonal meridional march of summer precipitation anomalies over eastern China and possible mechanism
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    Abstract:

    Understanding the classification of the subseasonal meridional march of summer precipitation anomalies in eastern China has important influence on understanding dynamic process of East Asian summer monsoon and prediction of rainband. However, previous studies for classification of precipitation focus on subseasonal propagation for local precipitation, while the regularity and classification of subseasonal march of summer precipitation anomalies over eastern China is still unclear. Therefore, in this study the subseasonal meridional movement of summer (24-50 pentad) precipitation anomalies over eastern China has been classified into three categories by using K-means clustering method: 1) the northward propagating type in which the precipitation anomalies move northward from South China; 2) the oscillating type in which the precipitation anomalies are stable and the phase is reverse in the north and south of 30oN; 3) the southward retreating type in which the precipitation anomalies move southward from the Huang-Huai River Basin. Furthermore, it can be observed that the anomalous convection over tropical Indian Ocean propagates northeastward in all three types. However, whether the precipitation anomalies can propagate to eastern China largely depends on the movement speed and intensity of the mid-latitude disturbance over East Asia. When the westerly jet over eastern China is strong and wide, the mid-latitude disturbance moves eastward quickly. While the wave activity flux propagated to East Asia is inactive, the mid-latitude disturbance is hard to develop. In this case, tropical anomalous convection is prone to propagate northward and form the northward propagating type. If the westerly jet over eastern China is weak but the wave activity flux propagated to East Asia is active, the mid-latitude disturbance moves slowly and is stable. It can develop and enhance due to active upstream wave energy transport, thus blocking the northward propagating of the tropical anomalous convection and forming the oscillating type. When the westerly jet over eastern China is strong and wide, and the wave activity flux transported to East Asia is active, the mid-latitude disturbance can be strengthened and propagate southward, formulating southward retreating type.

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History
  • Received:November 10,2023
  • Revised:February 23,2024
  • Adopted:July 19,2024
  • Online: September 04,2024
  • Published: