It has been a longstanding problem for current weather/climate models to accurately predict summer heavy precipitation
over the Yangtze-Huaihe Region (YHR) which is the key flood-prone area in China with intensive population and
developed economy. Large uncertainty has been identified with model deficiencies in representing precipitation processes
such as microphysics and cumulus parameterizations. This study focuses on examining the effects of microphysics
parameterization on the simulation of different type of heavy precipitation over the YHR taking into account two different
cumulus schemes. All regional persistent heavy precipitation events over the YHR during 2008-2012 are classified into
three types according to their weather patterns: the type I associated with stationary front, the type II directly associated
with typhoon or with its spiral rain band, and the type III associated with strong convection along the edge of the
Subtropical High. Sixteen groups of experiments are conducted for three selected cases with different types and a local
short-time rainstorm in Shanghai, using the WRF model with eight microphysics and two cumulus schemes. Results show
that microphysics parameterization has large but different impacts on the location and intensity of regional heavy
precipitation centers. The Ferrier (microphysics) –BMJ (cumulus) scheme and Thompson (microphysics) – KF (cumulus)
scheme most realistically simulates the rain-bands with the center location and intensity for type I and II respectively. For
type III, the Lin microphysics scheme shows advantages in regional persistent cases over YHR, while the WSM5
microphysics scheme is better in local short-term case, both with the BMJ cumulus scheme.
A typical heavy rainfall event occurred in Shanghai on September 13, 2009 was simulated using the Weather Research and Forecasting Model (WRF) to study the impact of microphysics parameterization on heavy precipitation simulations. Sensitivity experiments were conducted using the cumulus parameterization scheme of Betts-Miller-Janjic (BMJ), but with three different microphysics schemes (Lin et al, WRF Single-Moment 5-class scheme (WSM5) and WRF Single-Moment 6-class scheme (WSM6)) under three-way nested domains with horizontal resolutions of 36km, 12km and 4km. The results showed that all three microphysics schemes are able to capture the general pattern of this heavy rainfall event, but differ in simulating the location, center and intensity of precipitation. Specifically, the Lin scheme overestimated the rainfall intensity and simulated the rainfall location drifting northeastwards. However, the WSM5 scheme better simulated the rainfall location but stronger intensity than the observation, while the WSM6 scheme better produced the rainfall intensity, but with an unrealistic rainfall area.
KEYWORDS: Clouds, Data modeling, Atmospheric modeling, Convection, Meteorology, Monte Carlo methods, Data centers, Computer simulations, Systems modeling, Physics
The Weather Research and Forecast Model (WRF) version 3.5 has been used in this study to simulate a heavy rainfall event during the Meiyu season that occurred between 1 and 2 July 2014 over the Yangtze River valley (YRV) in China. The WRF model is driven by the National Centers for Environmental Predictions (NCEP) Final (FNL) global tropospheric analysis data, and eight WRF nested experiments using four different microphysics (MP) schemes and two cumulus parameterizations (CP) are conducted to evaluate the effects of these microphysics and cumulus schemes on heavy rainfall predictions over YRV region. The four MPs selected in this study are Lin et al., WRF Single-Moment 3-class scheme (WSM3), WRF Single-Moment 5-class scheme (WSM5) and WRF Single-Moment 6-class scheme (WSM6), and the two CPs are Kain-Fristch (KF) and Betts-Miller-Janjic (BMJ) schemes. Sensitivity studies showed that all MPs coupling with KF and BMJ CP schemes can well capture the major rain belt from the northeast to southwest with three rainfall centers, but largely overestimate the rainfall near the border between Anhui and Hubei provinces along with the Yellow Sea shore, which produce an opposite trend compared to the observations. Large discrepancies are also presented in WRF simulations of heavy rainfall centers regarding their locations and magnitudes. All MPs coupling with KF CP scheme produced the rainfall areas shifting towards east compared to the observations, while all MPs with BMJ CP scheme tend to better predict the rainfall patterns with slightly more fake precipitation centers. Among all the experiments, the BMJ cumulus scheme has superiority in simulating the Meiyu rainfall over the KF scheme, and the WSM5–BMJ combination shows the best predictive skills.
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