Interdecadal variations and possible causes of rain belt’s advancing velocity in Eastern China based on evolutionary circulation pattern

This study verifies the capability of evolutionary circulation to characterize the movement of rain belt based on Self-Organizing Map (SOM) and further explores the interdecadal variation of rain belt’s northward advancement during flood season in eastern China. The results show that the evolving path of circulation patterns can effectively describe the trajectory of rain belt’s movement with a significant correlation coefficient of 0.91. By employing the time required for circulation evolution to represent the velocity of rain belt’s movement, the northward velocity of rain belt emerges interdecadal shifts around the mid-late1970s and the late 1990s, which is affected by the sea surface temperature anomaly of Pacific Decadal Oscillation (PDO) pattern. During negative PDO phases, the warming of western North Pacific and the cooling in equatorial middle-east Pacific trigger the northward westerly jet and Western Pacific Subtropical High, leading to the northward vertical upward motion. This configuration encourages the circulation pattern corresponding to Yangtze-Huaihe River basin rain belt to transfer to that representing more precipitation in North and Northeast China, resulting in the accelerated northward advance of rain belt. Conversely, during positive PDO phases, the moisture brought by westward subtropical high and upward motion driven by the southward upper jet stream increase the likelihood of persistent precipitation in Yangtze-Huaihe River Basin, slowing the advancement of rain belt. During the phase transition of PDO, the northward leap of circulation systems in July has been proved to play a pivotal role in the interdecadal variation of rain belt’s overall advancing velocity.