The 2019 Autumn Hot Drought Over the Middle-Lower Reaches of the Yangtze River in China: Early Propagation, Process Evolution, and Concurrence

摘要

Hot droughts (i.e., concurrent droughts and hot anomalies) have drawn much attention recently, but current knowledge about early propagation and concurrence remains limited. The 2019 autumn severe hot drought (2019AHD) over the middle-lower reaches of the Yangtze River (MLYR) is employed for process-based analysis, while water vapor transport, heating budgets, and atmospheric dynamics are comprehensively investigated. The main achievements are as follows: (a) The 2019AHD over MLYR is not isolated and is related to early propagation from adjacent North China (NC) two months earlier. (b) Direct physical causes are explored. Drought evolution is related to anomalous water vapor transport dominated by low-level cyclonic anomalies over the East China Sea. Concurrently, local lowlevel hot anomalies over MLYR are related to amplified horizontal advection heating, while near-surface warming is favored by decreased low cloud cover and enhanced downward shortwave radiation. (c) Regional-scale concurrence of droughts and hot extremes might be understood by the combined effects of amplified subsidence (suppressing precipitation formation) and intensified low-level divergence (reducing low cloud cover). (d) From a large-scale dynamic perspective, early propagation and development of the 2019AHD are related to the southward shift and enhancement of the subsidence branch of meridional circulations. Meanwhile, intensity variation in 200 hPa cyclonic anomalies over MLYR corresponds well with local drought development, and the enhanced intensity at the time of drought occurrence is probably related to Silk Road Pattern-like wave train propagation over Eurasia. These insights can help us understand the mechanisms and detect early signals of hot droughts.