Corridors of mei-yu-season rainfall over Eastern China

Abstract

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 278-318N. 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 inthe 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 expressesa joint influence of the blocking patterns inmidlatitudes 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.