边界层参数化和湿过程对切变线低涡发展影响的中尺度模拟

Mesoscale Numerical Simulation of the Influence of PBL Parameterization and Moist Process on Development ofa Shear-Line Vortex

1981年8月14至22日,在青藏高原东侧陕、甘、川毗邻区,出现了一次持续暴雨过程.对其主过程的涡度诊断表明,切变线低涡初生於青藏高原东侧低空,其后,不仅出现了高、低空涡度中心的叠加和耦合过程,而且在行星边界层(PBL)内发生了迅速加强过程.这种过程与切变低涡的持续发展相伴. 一系列48和72小时中尺度数值模拟结果揭示:只有高分辨PBL参数化的湿物理过程,才能较好地模拟出切变低涡在PBL内的突然加强及其涡度演变和垂直结构;而总体PBL参数化,虽然其涡度演变和垂直结构也能基本模拟出来,但不能模拟出切变线低涡在PBL内的迅速加强;总体PBL参数化干过程的模拟结果指出,该方案较前两种湿过程方案均差,特别是被模拟系统的强度明显减弱,位置偏离. 模拟与诊断和观测之间的比较揭示,尽可能仔细地改进PBL参数化和湿物理过程,才有可能改进对这类中尺度系统发生和发展的模拟.

During the period of 14-22 August 1981 , a persistent heavy rainfall event occurred over adjoining region of Shanxi, Gansu and Sichuan provinces which are located on the eastern side of the Tibetan Plateau. The vorticity diagnosis of the main heavy rainfall event showed that the shear-line vortex originated in lower level of the eastern side of the Tibetan Plateau . Following that event, not only vorticity centers superimposed and conpled at the upperand lower-level , but also an intensive process took place rapidly in the PBL. This process was accompanying by persistent development of the shear line vortex.A series of 48 hr and 72 hr mesoscale numerical simulations reveal that only the high resolution PBL parameterization with moist process can well simulate the rapidly intensive process in the PBL, vorticity evolution and vertical structure of the shear-line vortex . The bulk PBL parameterization can not simulate this rapidly intensive process of the shear-line vortex although its vorticity evolution and vertical structure can beroughly simulated . The simulative result of the bulk PBL parameterization with dry process indicates that this scheme is worse than the two schemes with moist processes as mentioned above , especially , the intension of simulated shear-line vortex was significantly weaken and the location deviated.The comparisons of the simulations , diagnoses and observations reveal that only by improving PBL parameterization and moist physical processes as careful as possible can we improve the simulations of the formation and development of this kind of mesoscale systems.