陕西中西部地区一次暴雨过程的数值模拟研究

Numerical Simulation Studies on a Rainstorm in Central Western Shaanxi Province

利用多种观测资料和NCEP再分析资料,分析了2011年7月28-29日发生在陕西中西部地区的一次中尺度系统暴雨过程,运用WRF模式模拟研究了此次暴雨过程的中尺度系统环流特征及其发生、发展的动力和热力特征。结果表明,此次暴雨过程与高空槽的发展演变密切相关,低空切变线是暴雨过程产生的中尺度系统。暴雨区存在弱低空辐合与强高空辐散,正相对涡度与垂直上升运动明显;暴雨发生前对流有效位能(CAPE)明显增大,未来3 h降水区域位于850 h Pa切变线和CAPE高值区附近,强垂直运动触发CAPE的释放,使其在12 h内减少量达2200 J·kg-1,是形成此次暴雨的重要因素。暴雨发生、发展过程中,非线性平衡方程残差大值区与未来1 h降水区相对应,与质量场和动量场之间的调整有密切关系,大气运动的不平衡通过散度场的变化调节,在中尺度区域激发出辐合、辐散的快速增长,从而激发出暴雨天气,非线性平衡方程残差值是表征激发暴雨天气的重要动力因子。

The circulation feature of a mesoscale system and its dynamical and thermal characteristics in the phase of development are studied through analyzing and simulating for the rainstorm process which occurred in central Western Shaanxi province during 28-29 July 2011 by observational data,NCEP final analysis data and high resolution output by mesoscale model WRF V3. 4. Synoptic analyses indicate that upper troughs and low level shear are the main weather systems for this rainstorm. Diagnoses of the physics fields suggest that stronger upper divergence and week low er convergence associated with positive vorticity and strong vertical motions in the strong precipitation region during the developing phase of the rainstorm. At the initial phase of the rainstorm,Convective Available Potential Energy(CAPE) was accumulated and which was triggered and released rapidly(decrease2200 J·kg-1in 12 hours) by the strong vertical motions,which causes such a strong rainstorm. The strong precipitation in 3 hours occurred around the shear line on 850 h Pa which was associated with high CAPE value. The analysis on the residual of Non-linear Balance Equation(NBE) features shows that the high residual of NBE appeared around the heavy precipitation area,which has close relationship with the adjustment betw een momentum and mass field.