Diurnal cycles of Mei-yu rainfall simulated over eastern China: Sensitivity to cumulus convective parameterization

Realistic simulation of the diurnal cycle of rainfall has been regarded as one of the challenging issues. This study investigates the sensitivity of simulating the diurnal cycle of Mei-yu rainfall over eastern China to cumulus parameterization schemes (CPSs) and the associated physical mechanisms using WRF model. Although CPSs reproduce well the late-afternoon peak of rainfall, they differ largely in simulating the early-morning peak that is closely associated with the eastward-propagating (locally-growing) nocturnal systems over the eastern slope of the Tibetan Plateau (lower reach of the Yangtze River valley). The Kain-Fritsch (KF) scheme with an alternative trigger function (KFtrigger2) shows the best performance on capturing the diurnal phase and amplitude of rainfalls. Compared to the KFtrigger2 scheme, the KF scheme enhances moisture convergence and terrain-induced circulations that are favorable for the propagating rainfall systems in the western region. The intensive southerly wind due to inertial oscillation, with stronger upward motion and moisture convergence and higher convective available potential energy (CAPE), also lead to more locally-growing nocturnal rainfall in the eastern region. The Betts-Miller-Janjic scheme produces a more stable atmosphere with weaker upward motion and smaller CAPE, resulting in a poor simulation of convective and non-convective rainfalls with a 2-h delay for the peaks of two kinds of nocturnal systems. The Grell-3D scheme produces the relatively weak and short-lived propagating nocturnal rainfall owing to the weaker circulation and drier conditions in the middle troposphere. However, it reproduces the unstable atmosphere with relatively strong upward motion and moisture convergence, resulting in more convective rainfall in the locally-growing nocturnal systems.