ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 43 Issue 5 > 2017,43(5):513-527. DOI:10.7519/j.issn.1000-0526.2017.05.001 Prev Next
Uncertainty Analysis on the July 2016 Extreme Precipitation Event in North China Using ConvectionAllowing Ensemble Simulation
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Abstract:
Convectiveallowing ensemble forecasting experiments were applied for an extreme precipitation event in North China in 18-20 July 2016. Uniform initial condition and boundary condition were used for ensemble simulations with 13 members based on varied WRFARW microphysics at 4 km horizontal resolution. The intensity and spatiotemporal distribution of simulated precipitation were similar to precipitation observation, and significant uncertainties were proved to be among ensemble members. Accuracy of rainfall simulation was improved compared with global numerical model, and members with Morrison scheme and WSM6_P2 scheme achieved better results verified by methods of neighborhood ETS, correlation, and RMSE. Rainfall’s probability density function showed that bias of excessive rainfall dominates below 50 mm rainfall prediction, and deficient bias of precipitation dominates above 100 mm. Significant spread was found in the intensity of upperlevel jet and path of surface cyclone in the ensemble simulation experiments. Correlation analysis between precipitation and diagnosed variables including precipitable water, lowlevel relative vorticity and vertical motion proved that ensemble members could be divided into severe precipitation and weak precipitation. The subdivision with severe precipitation features severe convective echoes, strong subsidence, intense cool pool, and significant positive potential vorticity anomaly in midlower level due to latent heating which takes effect on subsequent evolution of weather system. Warm cloud process plays an important role in weak precipitation with relatively weak radar echoes, weak cool pool which is much more close to the steady stratiform precipitation process in fact. Radar reflectivity simulated by several kinds of 2moment microphysics schemes is characterized by “bright belt” echoes around 0℃ level, and separation between convection and stratiform cloud is more realistic compared with simulation results of 1moment microphysics schemes. With different settings of several key parameters in the WSM6 scheme, two types of precipitation processes were identified as severe convective storm and intense warm cloud precipitation, so uncertainties in the convectivescale physical process could be estimated for specific synoptic event which indicates the superiority of ensemble forecasting based on varied microphysics.
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