A Synchronous Variation Process of Tibetan Plateau Vortex and Southwest Vortex

The synchronous variation of Tibetan Plateau vortex (TPV) and southwest vortex (SWV) is an important way to trigger heavy precipitation in southwest and eastern China. However, the physical process and mechanism of the coordinated change of two vortices are still unclear. A synchronous variation process of the TPV and SWV during the super-strong and super-long Meiyu period in 2020 (during 1-4 June of 2020) is selected to analyze the evolution characteristics of the strength and structure corresponding to the special time node (T1-T5) when two vortices coexist, as well as the potential vorticity budget with the data including the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5) hourly data and the precipitation observations. It's found that during the period T1-T2, TPV moves eastward on the Tibetan Plateau. When the SWV is generated (T1), it is far away from the TPV, and it is considered that two vortices have no interaction at that time. At the time of T3, when the TPV moves to the lower slope terrain on the eastern side of the Tibetan Plateau, its intensity is significantly weakened. Also at that monment, the TPV begins to change in coordination with the SWV. During T4-T5, two vortices strengthen and continue to change synchronously, and then merge into cyclonic circulation on their east side. Combined with the intensity changes of two vortices, the TPV and SWV with non-overlapping horizontal positions can also undergo synchronous variations, when their characteristics of intensity changes are roughly similar. From the analysis results of the potential vorticity diagnostic equation, two vortices have different evolution mechanisms before the synchronous variation, but their evolution mechanisms are basically the same when the synchronous variation occurs. It can be concluded that, when there is no synchronous variation (T1-T2), the TPV mainly relies on the heating field to maintain the eastward movement, and the SWV is maintained by the horizontal potential vorticity flux divergence. When the two vortices change synchronously (T3-T5), their intensity changes are similar, and the evolution mechanisms of them are consistent. The maintenance of two vortices mainly depends on the horizontal potential vorticity flux divergence, followed by the heating field.