Synoptic features of cyclones and rainstorm in Huang-Huai region during the warm season (May－September) from 1990 to 2022

To deepen the understanding of the activity characteristics of Huang-Huai Cyclones (HHCs) and their associated rainstorm weather features, based on the ERA5 reanalysis data and daily precipitation data from national meteorological stations in the Huang-Huai region, this study investigates the activity characteristics of HHCs and the weather characteristics of their induced rainstorm weather during the warm season(May—September) from 1990 to 2022 by employing objective identification and statistical methods for HHCs. Meanwhile, synoptic classification of HHCs-induced rainstorms is objectively typed by a combined method of T-PCA and K-means, and the distribution characteristics of heavy precipitation under each synoptic pattern are analyzed. The results show that the source center of warm-season HHCs is located in the central Huang-Huai region during 1990–2022, and the junction of Henan, Anhui, Shandong and Jiangsu provinces is the high-frequency center of their activity. The number of HHCs days has shown an increasing trend at a rate of 1.9 days per decade, while the numbers of rainstorm days,HHCs-induced rainstorm days, and HHCs-induced regional rainstorm days remained relatively stable.All four parameters exhibited a decadal variation characterized by an initial decrease followed by an increase after 2010. About 44% of HHCs can trigger rainstorms during the warm season, and this proportion reaches 70% in July–August; strong HHCs are more likely to induce regional heavy rainstorms. In May, only 32% of HHCs can trigger rainstorms, but HHCs-induced rainstorm days account for 49% of the total rainstorm days in that month, indicating that HHCs are an important synoptic system for rainstorms in the Huang-Huai region during late spring. The large-scale circulation patterns associated with HHCs-induced rainstorms during the warm season can be classified into three categories: the Western Pacific Subtropical High (WPSH) and trough pattern, the WPSH edge pattern, and the westerly trough pattern. The WPSH and trough pattern contributed the most to scattered rainstorms, with a proportion of 47.2%, while the westerly trough pattern accounted for the largest share (37.9%) in regional rainstorms.This study improves the understanding of the characteristics of HHCs and their associated rainstorms, and can provide a scientific reference for the forecasting of this type of rainstorm.