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Successive mesoscale convective systems may develop for several days during the mei-yu season (June–July) over eastern China. They can yield excessive rainfall in a narrow latitudinal band (called a corridor), causing severe floods. The climatology of rainfall corridors and related environmental factors are examined using 20 yr of satellite rainfall and atmospheric data. A total of 93 corridors are observed over eastern China, with maximum occurrence at 27°–31°N. They typically last 2–3 days, but some persist ≥4 days, with an extreme event lasting 11 days. These multiday convective episodes exhibit primary and secondary peaks in the morning and afternoon, respectively, with a diurnal cycle that is in contrast to other afternoon-peak rain events. On average, the corridors occur in ~23% days of the mei-yu season, but they can contribute ~51% of the total rainfall. They also vary with years and explain ~70% of the interannual variance of mei-yu-season rainfall. Composite analyses show that most corridors develop along zonally oriented quasi-stationary mei-yu fronts over central China where monsoon southwesterlies converge with northerly anomalies from the midlatitudes. The monsoon flow accelerates at ~0200 LST and forms a regional wind maximum or low-level jet over South China, which induces moisture flux convergence in morning-peak corridors. The nocturnal acceleration is less evident for afternoon-peak corridors. The mei-yu front and monsoon southwesterlies also influence the corridor's duration, which is regulated by a dipole of geopotential anomalies, with positive in the tropics and negative in the midlatitudes. The dipole expresses a joint influence of the blocking patterns in midlatitudes and the El Niño–related anomalous high over the western Pacific Ocean, and the dipole's intensity explains well the interannual variations of the corridors. [ABSTRACT FROM AUTHOR]

A succession of MCSs developed during the last week of October 2016 and produced extreme heavy rainfall in central China. The event underwent an evident shift from a mei-yu-like warm scenario to an autumn cold scenario. Diurnal cycles of rainfall and low-level winds may be modulated by the shifting of large-scale atmospheric conditions. We conducted observational analyses and numerical experiments to examine how large-scale circulations influenced rainfall systems through diurnally varying processes. The results show that, in the first half (warm) period of the event, intense rainfall mostly occurred in eastern-central China with an early morning peak. It was closely related to a nocturnal southwesterly low-level jet (NLLJ) on the flank of the western Pacific subtropical high. The NLLJ formed near midnight in southern China where ageostrophic wind rotated clockwise due to Blackadar's inertial oscillation. The NLLJ extended downstream to central China during the predawn hours due to the horizontal advection of momentum. Both the formation and extension of the NLLJ were supported by an enhanced subtropical high that provided relatively warm conditions with surface heating for boundary layer inertial oscillation and strong background southwesterly winds for momentum transport. The NLLJ induced MCSs at its northern terminus where the low-level ascent, moisture flux convergence, and convective instability were enhanced during the predawn hours. In the second half period with an intrusion of cold air, the diurnal amplitude of low-level winds became small under relatively cold and cloudy conditions. Moderate rainfall tended to occur in western-central China with a peak after midnight, most likely due to frontogenetic processes, upslope lifting, and nighttime cloud-top cooling. [ABSTRACT FROM AUTHOR]