摘要
利用新一代WRF模式模拟了2003年7月8—10日的江淮暴雨,就WRF模式中的MRF和MYJ边界层参数化方案进行了对比试验。发现分辨率为20 km时,WRF模式基本上能够模拟出中尺度降水的范围、位置和强度。采用边界层方案显然比不采用边界层方案的模拟效果好,但是MYJ方案与MRF方案相比并没有明显的优越性。另外发现边界层物理过程对格点尺度降水影响很小,模式主要通过边界层物理过程和积云对流过程之间的耦合,来改善对流性降水的模拟。
The planetary boundary layer （PBL） is the region of the atmosphere near the surface where the influence of the surface is through the turbulent exchange of momentum, heat and moisture. The transition region between the surface and the free atmosphere, where vertical diffusion due to turbulent motion takes place, varies in depth. The PBL can be as shallow as 100 m during night over land and go up to a few thousand meters when the atmosphere is heated from the surface. The PBL is directly influenced by the Earth＇ s surface, responding to such forces as frictional drag, solar heating, and evapotranspiration, so its parametrization determines together by the surface parametrization, the surface fluxes and the redistributes the surface fluxes over the boundary layer depth.
Although the precipitation variation is described by the microphysics and the cumulus convection in physics process, the PBL structure plays an important role in the successful determination of the precipitation prediction, because other processes can not be parametrized properly without having a PBL scheme. The new generation mesoscale model WRF is used to simulate the Jianghuai heavy rainfall during July 8--11, 2003, and the precipitation sensitivity to PBL parameterization scheme is tested. All sensitivity simulations are initialized at 00：00 （UTC） each day with NCEP/NCAR reanalysis data. The results show that WRF model can reproduce the area, the location and the daily rainfall of the precipitation well, and the sensitivity of the precipitation simulation to the boundary layer physics is quite high. Using the PBL scheme can improve the precipitation simulation significantly. MYJ scheme has no significant improvement on precipitation simulation compared with MRF scheme when the horizontal resolution is 20 km.
Detailed diagnoses are carried out on Huaihe heavy rainfall on July 9, 2003 to examine the impact of the PBL on precipitation simulation. The analysis on the vapor flux on 850 hPa shows that the vapor in heavy rainfall area comes from the Bay of Bengal, and the PBL process can enhance the convergence of the vapor in low layer. In all experiments, the large-scale precipitation is produced to the northeast of the convection portion. The comparison between the two portion of the precipitation shows that PBL process has little effect on grid scale precipitation, and the improvement of the PBL to precipitation simulation is directly related to the location and the precipitation of convective rainfall. PBL physics can increase the upward vertical velocity in heavy rainfall area and enhance the convective intensity according to the analysis on the vertical section of the vertical velocity. The K index tests show that PBL process increases the stratification instability, and then strengthens the convection.
All of the diagnose analysis show that the improvement of the precipitation simulation with the PBL scheme should be attributed to the strong coupling between the boundary layer physics and the convective process.
出处
《应用气象学报》
CSCD
北大核心
2006年第B08期11-17,共7页
Journal of Applied Meteorological Science
基金
科技部"奥运气象保障技术研究"课题(2002BA904B05)
北京市自然科学基金重点项目(8051002)
国家气象中心自由项目(ZK2005-09)
国家科技攻关计划"北京奥运国际天气预报示范计划关键技术研究"(2003BA904B09)共同资助
关键词
WRF模式
边界层参数化方案
格点尺度降水
对流性降水
WRF model
PBL parameterization scheme
grid scale precipitation
cumulus convective precipitation
