Abstract:Based on the daily observations of precipitation and sunshine duration from China Meteorological Administration and the NCEP/NCAR reanalysis data, this paper analyzes the extremity features of a high-impact “wheat-soaked persistent rainfall” event in the Huang-Huai-Hai Plain, which covers the five provinces of Hebei, Shandong, Henan, Jiangsu and Anhui, in late May of 2023 and the atmospheric circulation patterns. The findings suggest that, for the dekad average of five provinces during 21-31 May, the extremity of absent sunshine is more intense than precipitation. However, obvious differences exist among the five provinces, of which the situation in Henan Province is the most serious. To compare both the weather condition and the circulation pattern with historical events, this paper proposes an objective definition of “wheat-soaked persistent rainfall” event in Henan Province for the first time and selects out 18 typical cases during 1981-2022. For the “wheat-soaked persistent rainfall” event in late May 2023, it has the sixth highest rainfall amount and the second lowest sunshine duration among all events. The synthesis of general circulation patterns displays a more westward-northward and stronger western Pacific subtropical high (WPSH), and a “lower in the west while higher in the east” geopotential height anomaly in the mid-high latitudes of Eurasia. Therefore, for Henan Province, the extremity of absent sunshine is more obvious. The results of the synthesis of all events from 1981 to 2022 show that the large-scale atmospheric circulation pattern that causes the “wheat-soaked persistent rainfall” event is that the WPSH is westward stronger and the its western ridge line is northward, while the middle and high latitudes of Eurasia are under the “low in the west and high in the east” circulation pattern. In contrast, the circulation pattern of the “wheat-soaked persistent rainfall” event in late May 2023 is similar to that of the historical events in the mid-high latitudes. However, in tropical regions, affected by the Super Typhoon Mawar, the western section of the WPSH is squeezed and deformed, and the moisture transport by the southwesterly wind in the northwest side of the WPSH is significantly much stronger. At the same time, because “Mawar” remain stable near the east of the Philippines for a long time, the southeast wind flow guide by the northeast side of the typhoon is stronger than the southwest wind anomaly on the northwest side of the subtropical high. The two branches of water vapor superpose, leading to persistent precipitation and long-time absence of sunshine in the Huang-Huai-Hai Plain.