摘要
在暴雨系统中,大量降水会造成湿空气质量的亏损,这种湿空气质量亏损对暴雨系统的发生、发展有一定的强迫作用,称之为"质量强迫"。本文首先从理论上通过对连续方程进行修改,重新推导了ARPS模式中考虑质量强迫作用的扰动气压倾向方程,并利用该模式对一次华北冷锋暴雨过程进行质量强迫作用的数值模拟试验,详细分析了质量强迫引起的云微物理过程的变化。对比分析表明:(1)质量强迫项影响系统的降水量。在本文个例中,质量强迫项起主要作用的高度在5.75 km左右,使得大气产生了由该层向上、向下的运动调整,其中向下的运动调整不利于低层对流的上升运动,减弱了系统的对流强度,导致中心降水量有所减少。(2)云水场的分布与质量强迫项的分布吻合较好;降水率的变化和质量强迫项的变化趋势相似,且在5.75 km高度上表现明显;降水粒子下落末速度项是引起质量强迫项变化的主要原因。(3)湿空气质量场发生改变将使局地气压发生变化,这种变化又使动力场发生相应的调整,产生辐合、辐散及垂直运动。反之,运动场的调整也影响到气压场的调整,它们之间将是一个相互影响的过程,近而对天气系统发展强度产生较明显的作用。(4)对对比试验中模式控制方程各项的差别分析发现:造成扰动气压局地变化项差的主要原因是由散度项差与垂直速度项差共同作用造成的,其中,质量强迫项差起了间接的作用;造成水汽及云水物质局地变化项差的主要原因是微物理源汇项差,其次是降水粒子下落末速度项差。
In rainstorm system, mass of wet air can be decreased by heavy precipitation, and this decrease introduces a force on the development of rainstorm and this force is called ＂mass forcing＂ in this article. First, the tendency equation of perturbation pressure for ARPS numerical model, which includes mass forcing, is deduced by introducing a modified continuity equation. Secondly, with this model, a cold- front rainstorm in North China is simulated and diagnosed. Result shows： （1）Mass forcing can influence the amount of precipitation. For this rainstorm process, the maximum mass forcing shows up in the height of 5750 m where both the water vapor condensation and pressure declination are strong, also it produces both upward and downward movement of the air flow. Furthermore, the downward movement suppresses the rising movement of lower inflow, which decreases the amount of precipitation and downgrades the rainstorm. （2）The distribution of mass forcing is coincide with that of cloud water content. The change of mass force agrees with that of precipitation rate, especially in the height of 5750 m. The terminal falling speed of hydrometeor places the biggest influence on the mass forcing. （3） The change of local pressure field caused by change of wet air mass field can result in adjustment of dynamic field, such as convergent, divergent and vertical movement. Reciprocally, the change of dynamic field can also affect the pressure field. So this interacting process will yield visible effect on the intensity of rainstorm. （4）The dominating terms which lead to different local perturbation pressuress are the difference of convergent term and that of vertical term, while that mass forcing has an indirect effect on it. The leading term which controls the distribution of local water vapor and water material is the difference of microphysical term, followed by the terminal falling speed of hydrometeor.
出处
《高原气象》
CSCD
北大核心
2009年第2期278-292,共15页
Plateau Meteorology
基金
国家杰出青年基金项目(40428002)
国家自然科学基金面上项目(40375016,40405007)共同资助
关键词
华北暴雨
质量强迫
数值模拟
扰动气压倾向方程
微物理过程
Rainstorm
Mass forcing
Numerical simulation
Tendency equation of perturbation pressure
Microphysical process
