363339 Diurnal Cycles of Mei-yu Rainfall Simulated over Eastern China: Sentivity to cumulus convective parameterization

Wednesday, 15 January 2020
Hall B1 (Boston Convention and Exhibition Center)
Xi Lu, Sun Yat-sen University, Guangzhou, China

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.
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