Numerical study of influence of clo udhydrometeor advections on precipitable cloud system

Advection transport effects by wind field is a very important macrosco pically dynamical process for weather systems in real atmosphere. Cloud hydromet eor advections by threedimensional velocity vector are closely related to evol ution of precipitable cloud system and connect the macroscopically dynamical pro cess with the temporal and spatial variations of cloud hydrometeors. The advecti on transport of cloud hydrometeors may increase or decrease the contents of clou d hydrometeors and change their spatial distributions so that the development of precipitable cloud system may be prompted or broken up. The purpose of this pap er is to investigate the influence of macroscopically dynamical process on cloud microphysical process by changing the cloud hydrometeor advection transports in the numeric simulation of a heavyrainfall event occurring in North China duri ng 00：00 UTC 12-00：00 UTC 13 August 2004. Combining the NCEP/NCAR real analysi s data and routine observations of surface level and sounding, the ARPS model is employed to carry out simulations of the heavy rainfall event, including one co ntrolli ng experiment and three numerical experiments in which the horizontal, vertical and total threedimensional advection transports of cloud hydrometeors were exc luded, respectively. The result showed that the simulated specific humidity was little influenced by the cloud hydrometeor advection transports. The threedime nsional advection transports of cloud hydrometeors was propitious to enrich the mixing ratios of snow and graupel, while the contents of cloud water, rain water and ice were held back. The horizontal advection transports of cloud hydrometeo rs contributed to the mixing ratios of ice and snow, and diminished the contents of cloud water and rain water. The vertical advection transports of cloud hydro meteors improved the mixing ratios of rain water, snow and graupel and at the sa me time, worsened the content of ice. The analysis of threedimensional advecti on transport effects showed that the influence of threedimensional advection t ransports of cloud hydrometeors on precipitable cloud system was realized via ad justing the source or sink of cloud hydrometeors produced by cloud microphysical processes and the sedimentation of precipitable hydrometeors (rain water, snow and graupel), and then changing the vertical spatial structures of cloud hydrome teors. In addition, the contribution of the advection transport of snow to itsel f was also important.