Regional and Temporal Variability of Atmospheric Conditions along the Meiyu-Baiu Front

Abstract

East Asia experiences a distinctive summer rainfall period, referred to as Meiyu in China and Baiu in Japan. The precipitation during the Meiyu-Baiu season is a critical component of summer rainfall, significantly impacting agriculture and economic development. While both Southeast China (SEC) and Japan (JPN) encounter the Meiyu-Baiu season from June to July, the structure of the Meiyu-Baiu front (MBF) differs between these regions. Utilizing daily ERA5 reanalysis data and a method that defines the MBF based on equivalent potential temperature, we analyzed precipitation patterns and atmospheric conditions during the East Asian monsoon season. The MBF demonstrates a distinct northward progression in SEC from early June to late July, whereas in JPN, the front moves northward from early June to mid-July, stagnating thereafter. Meiyu-Baiu precipitation correlates strongly with the position of the MBF during early June to mid-July, with two major precipitation centers identified in both SEC and JPN. Atmospheric conditions associated with the MBF exhibit clear regional and temporal variability. Compared to JPN, SEC features a stronger meridional humidity gradient, more pronounced upward motion, and a smaller meridional temperature gradient on the southern side of the MBF.