用新RIEMS模式研究陆面过程对暴雨的影响

Effects of Land Surface Process on Heavy Rain: A New RIEMS Model

对MM5模式中的MYE,MRF以及新引进的NB方案(E ε 1边界层参数化)3种边界层参数化方案耦合了陆面过程模式BATS,形成新的RIEMS模式.用此模式及原MM5模式对2个江淮暴个例进行了数值模拟以考察陆面过程对暴雨模拟的影响,同时也分析了加入BATS后模式对形势场和有关气象场的影响.结果表明加了BATS后,模式在降水场,形势场,低空急流等方面均优于原MM5模式,表明陆面过程短期天气过程也有重要影响.

The three boundary layer parameterization schemes in MM5,i.e.,MYE, MRF and NB(E_ε_1 Parameterization,i.e.,the eddy exchange coefficient is computed from the eddy kinetic energy E, and the predicted equations for E and the dissipation rate of the eddy kinetic energy ε are applied to compute E and ε,a diagnostic relation is applied to compute the mixing length l are incorporated with the land surface model BATS.At the same time,the radiation scheme in CCM3 is also applied and a new RIEMS model is thus formed.The new RIEMS model and the original MM5 model are used to simulate two cases of heavy rain in the YangtzeHuaihe area on May 10 and July 17 in 1998 and to study the effects of land surface process on the heavy rain simulation.Meanwhile,the effects of the inclusion of BATS on the synoptic situation and meteorological fields are also analyzed.The grid distance is 60 km with 60*60*16 grids; the center of the domain is 32°N,107°E;the NCEP reanalysis data are used for initial fields.The results show that the simulations of precipitation by the new RIEMS model are superior compared with the simulations by the MM5 model.The improvement of the precipitation simulation of the new RIEMS model is connected with the improvements of the synoptic situation,such as the pressure field over sea level and the stream field on 850 hPa;some meteorological fields such as low level jet,divergence etc.,which means that the land surface process also plays an important role in the shortrange synoptic process.The inclusion of BATS improves the computation of eddy exchange for the sensible and latent heat as well as momentum fluxes between ground and air. It also improves the simulations of process in the boundary layer and stream fields,low level jet,further divergence,vorticity etc.in the lower atmosphere,which results in the precipitation simulation.According to the simulation,the PBL parameterization simulation.According to the simulation the PBLparameterizations based on the eddy kinetic energy closure such as MYE and NB are slighter better,especially,the NB scheme.The results of the Grell cumulus parameterization scheme are better than those of the Kuo scheme.The new RIEMS model increases the choice of the parameterization of the PBL and land process schemes and is available for the long-term integration of the model in the climate research.The improvement of the inclusion of BATS is restricted and the dynamical structure of the model probably plays a more important role than the physical process parameterizations.