Impact on summer precipitation forecast by using different planetary boundary layer schemes in the WRF3D model

The impact on summer precipitation forecast in the central eastern China has been studied by using two different planetary boundary layer schemes (MYJ and ACM2) in the WRF3D model. Comparing to high resolution precipitation observations, results from sensitivity experiments in July 2012 show that the differences in precipitation forecast in the daytime (nighttime) are mainly determined by the rainfall area (rainfall intensity). Especially, the forecasts with the MYJ scheme give too large rainfall area in the daytime, and the forecasts with the ACM2 scheme give too strong rainfall intensity in the nighttime. Further diagnosis shows that the erroneously large rainfall area with the MYJ scheme is due to the trigger of cumulus convection scheme to produce large-scale implicit rainfall in the daytime, while it is more likely to provoke the cloud microphysics scheme to produce overly stronger explicit rainfall in the nighttime by using the ACM2 scheme. Finally, based on the different assumptions in each planetary boundary layer scheme, it is pointed out that the vertical mixing strength is the root cause of the differences in rainfall forecast.