Characteristics and Variations of Raindrop Size Distribution in Chengdu of the Western Sichuan Basin, China

Knowledge of the microphysical characteristics of precipitation plays a significant role in meteorology, hydrology, and natural hazards management, especially in the western Sichuan Basin (WSB), which is located east of the Tibetan Plateau (TP) in southwestern China and thus has unique terrain conditions and weather systems. Nonetheless, the literature regarding raindrop size distribution (RSD) in the WSB is still very limited. This work investigates RSD characteristics and temporal variations in a site (Chengdu, CD) of the WSB by employing three years of quality-controlled RSD observation collected from a second-generation PARSIVEL disdrometer. The results show that RSD has noticeable seasonal and diurnal variations in CD. Specifically, the broadest mean raindrop spectra can be found in summer and the narrowest in winter, and the raindrop spectra of a day can be the narrowest during 1400–1500 BJT (Beijing Standard Time, UTC+8). In addition, the mass-weighted mean diameter (Dm) is lower in the daytime than in the nighttime, while the logarithm of the generalized intercept parameter (log10Nw, the unit of the Nw is m−3 mm−1) has a larger value in the daytime than in the nighttime. In addition, intercomparisons indicate that the mean Dm of convective rains in CD is smaller than in South China and it is higher than in the eastern slope of TP, East China, and North China; on the other hand, the corresponding mean log10Nw is close to the value at the middle TP. Local empirical relations of shape–slope parameters (μ–Λ) and reflectivity–rain rate (Z–R) are also presented to provide references for optimizing the RSD parameterization scheme and radar precipitation estimation in the local area

Uncertainty Quantification of WRF Model for Rainfall Prediction over the Sichuan Basin, China

The mesoscale Weather Research and Forecasting (WRF) model has been widely employed to forecast day-ahead rainfalls. However, the deterministic predictions from the WRF model incorporate relatively large errors due to numerical discretization, inaccuracies in initial/boundary conditions and parameterizations, etc. Among them, the uncertainties in parameterization schemes have a huge impact on the forecasting skill of rainfalls, especially over the Sichuan Basin which is located east of the Tibetan Plateau in southwestern China. To figure out the impact of various parameterization schemes and their interactions on rainfall predictions over the Sichuan Basin, the Global Forecast System data are chosen as the initial/boundary conditions for the WRF model and 48 ensemble tests have been conducted based on different combinations of four microphysical (MP) schemes, four planetary boundary layer (PBL) schemes, and three cumulus (CU) schemes, for four rainfall cases in summer. Compared to the observations obtained from the Chinese ground-based and encrypted stations, it is found that the Goddard MP scheme together with the asymmetric convective model version 2 PBL scheme outperforms other combinations. Next, as the first step to explore further improvement of the WRF physical schemes, the polynomial chaos expansion (PCE) approach is then adopted to quantify the impacts of several empirical parameters with uncertainties in the WRF Single Moment 6-class (WSM6) MP scheme, the Yonsei University (YSU) PBL scheme and the Kain-Fritsch CU scheme on WRF rainfall predictions. The PCE statistics show that the uncertainty of the scaling factor applied to ice fall velocity in the WSM6 scheme and the profile shape exponent in the YSU scheme affects more dominantly the rainfall predictions in comparison with other parameters, which sheds a light on the importance of these schemes for the rainfall predictions over the Sichuan Basin and suggests the next step to further improve the physical schemes

The Southern China monsoon rainfall experiment (SCMREX)

The article of record as published may be found at http://dx.doi.org/10.1175/BAMS-D-15-00235.1A unique program is developed for improving heavy rainfall forecasts over southern China during the presummer rainy season through field campaigns and research on physical mechanisms and convection-permitting modeling.Public Welfare Scientific Research Projects in MeteorologyScientific Projects of the Chinese Academy of Meteorological Sciences (CAMS)Outreach Projects of the State Key Laboratory of Severe WeatherNational Basic Research Program of China (973 Program)GYHY201406013 (PWSRPM)GYHY201406003 (PWSRPM)GYHY201306004 (PWSRPM)GYHY201406007 (PWSRPM)2014Z004 (CAMS)2014LASW-B04 (OPSKLSW)2014LASW-B05 (OPSKLSW)2012CB417202 (973 Program)2014CB441402 (973 Program

The Southern China Monsoon Rainfall Experiment (SCMREX)

A unique program is developed for improving heavy rainfall forecasts over southern China during the presummer rainy season through field campaigns and research on physical mechanisms and convection-permitting modeling.Public Welfare Scientific Research Projects in Meteorology [GYHY201406013, GYHY201406003, GYHY201306004, GYHY201406007]; Scientific Research Projects of the Chinese Academy of Meteorological Sciences (CAMS) [2014Z004]; Outreach Projects of the State Key Laboratory of Severe Weather [2014LASW-B04, 2014LASW-B05]; National Basic Research Program of China (973 Program) [2012CB417202, 2014CB441402]SCI(E)ARTICLE5999-10139