Abstract:The low-frequency oscillation characteristics of continuous rainstorm processes in Guangdong during the pre-flood season in 2023 are analyzed by means of wavelet analysis and Lanczos temporal filter. The focus of this study is on revealing the mean atmospheric circulation field and its evolution characteristics in different phases of quasi-biweekly oscillations and the source of the low-frequency signals of the continuous warm-sector rainstorms with strong southwesterly winds in the northwest of Guangdong Province. The results show that the three continuous rainstorms exhibited a quasi-7-18 d periodic oscillation, located in the positive phase of two quasi-30-60 d intraseasonal oscillations. The continuous warm-sector rainstorms with strong southwesterly winds mainly occurred in the northwest of Guangdong in 22-26 June when there were stable “west blocking” and “east blocking” at the middle and high latitudes. During this period, the northwest of Guangdong was located at the bottom of the plateau trough and the edge of the western Pacific subtropical high at 500 hPa, and at the left side of southwest monsoon axis and the right side of the cyclonic circulations at 850 hPa. During the intermittent-start-peak period of the continuous warm-sector rainstorm processes with strong southwesterly winds, the low-frequency signals in the mid-to-upper levels originated from the southern branch wave train with the eastward propagation and southward extension of baroclinic low-frequency anticyclones and cyclones within or to the south of the Iranian Plateau and Qinghai-Xizang Plateau. The low-frequency signals in the lower levels arose from the eastward movement and southward extension of the eastern Mongolian Plateau low-frequency anticyclone and the progressively intensifying low-frequency cyclone east of the Sichuan Basin and Yunnan-Guizhou Plateau. They induced the center of South Asian high to move eastward gradually and the western Pacific subtropical high to weaken and retreat eastward. At the same time, the Qinghai-Xizang Plateau was controlled by low-frequency cyclonic circulation in intermittent periods and gradually became dominated by the low-frequency anticyclone circulation in the peak period, while North China and South China were controlled first by low-frequency anticyclone circulation in intermittent periods and then gradually by the low-frequency cyclonic circulation in the peak period. These findings could provide some references for medium-to-extended range forecasting of continuous warm-sector rainstorm.