Impact of the “Combined Modality” of Silk-Road and East Asia–Pacific Teleconnection Patterns on the Heavy Precipitation in the Early Stage of Meiyu in the Yangtze–Huaihe River Region in 2020

Using the daily reanalysis data of ERA5 (The fifth generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis of the global climate) and the daily station data of precipitation provided by the China Meteorological Administration, the influence of the “combined modality” of the Silk-Road (SR) pattern and East Asia–Pacific pattern (EAP) teleconnection on the heavy precipitation in the early stage of Meiyu in the Yangtze–Huaihe River region in 2020 is analyzed. The results showed that the “combined modality” could trigger continuous precipitation in the Yangtze–Huaihe River region. At the beginning of June 2020, the negative phases of the SR pattern and the positive phases of the EAP appeared simultaneously, and the phase difference maximized in June. The synergy of the two resulted in abnormal precipitation in the early stage of Meiyu in 2020. The main results are as follows. (1) The negative phases of the SR pattern accelerate the westerly jet stream, promoting strong divergence at 200 hPa over the Yangtze–Huaihe River region in the south of the jet stream’s entrance area. (2) The negative phases of the SR pattern are conducive to the eastward movement of the South Asia high, whereas the positive phases of the EAP are conducive to the westward movement of the western Pacific subtropical high, and the two move toward each other. The negative phases of the SR pattern and the positive phases of the EAP showed the largest difference on June 9, 2020. At this time, the South Asia high and western Pacific subtropical high overlapped at approximately 120°E, which is conducive to continuous precipitation in the Yangtze–Huaihe River region. (3) There are anomalous “cyclone–anticyclone” circulations at 850 hPa related to the positive phases of the EAP in the middle and low latitudes over East Asia, which makes the prevailing strong southwest airflow in the low altitudes (20°–35°N, 100°–125°E). The northerly airflow at middle latitudes is conducive to the transportation of dry and cold air to the south. It merges with the warm and humid southwest airflow over the Yangtze–Huaihe River region, leading to strong water vapor convergence and increasing the intensity of the local upward movement of the airflow.