What Is the Main Cause of Diurnal Variation and Nocturnal Peak of Summer Precipitation in Sichuan Basin, China? The Key Role of Boundary Layer Low‐Level Jet Inertial Oscillations

Abstract

The precipitation in Sichuan Basin (SB), China, exhibits pronounced diurnal variation, including minimum rainfall in daytime and a prominent peak near midnight. This study investigates the primary mechanism of precipitation diurnal variation in SB using forecasts from three summer months of 2013 produced at a 4‐km grid spacing. The model forecasts reproduce the observed spatial distributions and diurnal cycles well, including the peak precipitation in SB at around 02 local solar time (LST). Contrary to the common belief that emphasizes the solenoidal effects associated with the Tibetan and Yunnan‐Guizhou Plateaus, prominent diurnal inertial oscillations of boundary layer south‐southwesterly low‐level jet into SB are shown to play more important roles in modulating the diurnal cycles of precipitation in SB. A basinwide moisture budget analysis is performed to reveal that the moisture flux from the southeast side of the basin dominates within the diurnal oscillations of the net moisture flux into the basin, and the much enhanced nocturnal low‐level jet plays a crucial role in the formation of nocturnal precipitation within the basin. The net moisture flux into SB reaches maximum at around 22 LST, the time boundary layer perturbation winds from the daily mean in the direction normal to the southeastern boundary of SB reach maximum, which is about 4 hr before precipitation peak at around 02 LST. Shallow thermally forced nighttime downslope flows and daytime upslope flows on the Tibetan Plateau and Yunnan‐Guizhou Plateau slopes contribute only a small portion of moisture fluxes through the basin boundaries.

Diurnal Variation of Meiyu Rainfall in the Yangtze Plain During Atypical Meiyu Years

“…For instance, summer precipitation over south and northeast China peaks in the late afternoon , which is consistent with most land areas worldwide (Nesbitt & Zipser, 2003). The different diurnal cycles of summer precipitations in the Yangtze valley are thought to be related to the eastward movement of clouds over the Tibetan Plateau (Asai et al, 1998;Chen et al, 2014;Wang et al, 2004;Zhang et al, 2019). Summer precipitation in the lower reaches of the Yangtze valley has one diurnal peak in the early morning and another in the late afternoon .…”

“…Summer precipitation in the lower reaches of the Yangtze valley has one diurnal peak in the early morning and another in the late afternoon . The different diurnal cycles of summer precipitations in the Yangtze valley are thought to be related to the eastward movement of clouds over the Tibetan Plateau (Asai et al, 1998;Chen et al, 2014;Wang et al, 2004;Zhang et al, 2019).…”

Comparative Evaluation of the GPM IMERG Early, Late, and Final Hourly Precipitation Products Using the CMPA Data over Sichuan Basin of China

“…The basin floor can be divided into Chengdu plain, central Sichuan hill area, and east Sichuan parallel ridge-and-valley area. Studies show that, for Sichuan Basin of complex topography and geographic locations, the precipitation is unavoidably influenced by its landform, east Asian, south Asian, and plateau monsoons and has strong diurnal variations [50]. Precipitation statistics show that close to 70% of the total precipitation occurred at night, which is usually called "Bashan Yeyu" (nocturnal precipitation in Bashan Mountains) [51].…”

Elucidating the pollution characteristics of nitrate, sulfate and ammonium in PM<sub>2.5</sub> in Chengdu, southwest China, based on 3-year measurements

“…In recent years, with the rapid development of China's domestic economy and acceleration of urbanization, energy consumption and pollutant emissions have also increased, which increases the burden on the atmospheric environment, and severe air pollution has become a focus of social concern (X. G. An et al, 2019;Fu et al, 2014;Zhao et al, 2017). When air pollution forms, mass concentrations of particles with aerodynamic equivalent diameter ≤ 2.5 µm in ambient air (PM 2.5 , also known as fine particles) can reach a higher pollution level, which not only reduces atmospheric visibility but also carries a large number of toxic species into the human lungs, increasing the risks of cardiovascular and cerebrovascular diseases (Chang et al, 2018;Tie et al, 2009;Kong et al, 2019;Zhao et al, 2018;Y. R. Yang et al, 2015).…”