双流一次强降水的数值研究

Numerical Study on a Heavy Precipitation in Shuangliu Area

摘要: 为了进一步研究双流地区的强降水，本文用成都信息工程大学实习台中的常规天气图与温江探空资料，根据某次强降水过程前后的风场特征、层结状态及环流形势等，分析高低空的中小尺度天气系统对双流地区强降水的影响。再利用欧洲气象数据资料管理中心(ERA-interim)的再分析研究资料，从水汽条件、不稳定能量的释放和动力抬升作用等方面分析本次强降水过程的主要成因。通过天气学诊断分析方法，对双流2019年7月11日发生的一次强降水进行分析，结果表明：1) 发生在成都双流的此次降水是在高低空天气系统影响、共同作用下产生的对流性短时强降水过程。2) 首先，在水汽条件方面，双流区的比湿强度达到13 g/kg，水汽辐合中心的最大值达到−12 g∙cm⁻²∙hPa⁻¹∙s⁻¹。双流区上空较强的水汽辐合和比湿场为本次短时强降水提供了充足的条件。其次，在热力条件方面，双流地区正处于假相当位温高值中心范围内，θ_se达到80℃，∆θ_se500-850达到−10℃。最后，在动力条件方面，四川西南地区上空存在一个强度为−0.7 Pa∙s⁻¹左右的上升中心；双流地区850 hPa的涡度最大值为2∙s⁻¹，上升气流强盛，500 hPa上中心值为−4∙s⁻¹，为下沉气流，这种对流层中低层的正负涡度配置导致了对流层低层大气中不稳定能量的释放，促进了强降水天气过程的形成。3) 对温江站的探空资料进行分析，在降水前成都地区的K指数、沙氏指数和抬升指数的变化表明此时成都地区上空大气层结正从潜在不稳定向真实不稳定转变。CAPE指数的值相较于上午增加了几十倍，发生强对流天气的可能性大大增加。同时对流有效位能远远大于对流抑制能量的值，表明此时大气层结处于真潜不稳定状态，一旦低层大气中生成了小扰动，很容易打破CIN的束缚，进而发展成强对流。

Abstract: In order to further study the heavy precipitation in Shuangliu area, this paper, based on the wind field characteristics, stratification state and circulation pattern before and after a heavy precipitation process, analyzes the influence of high and low altitude mesoscale synoptic system on the heavy precipitation in Shuangliu area by using the conventional synoptic chart and Wenjiang radiosonde data in the practice platform of Chengdu University of Information Technology. Based on the reanalysis data from ERA-Interim, the main causes of the heavy precipitation process are analyzed from the water vapor conditions, the release of unstable energy and the dynamic lifting effect. Heavy precipitation occurring in Shuangliu area on July 11, 2019 was analyzed by means of synoptic diagnostic analysis method. The results show that: 1) The precipitation occurring in Shuangliu area was a short time convective heavy precipitation process under the influence of high and low altitude weather system. 2) First, in terms of water vapor conditions, the specific moisture intensity in Shuangliu area reaches 13 g/kg, and the maximum value of the water vapor convergence center reaches −12 g∙cm⁻²∙hPa⁻¹∙s⁻¹. The strong water vapor convergence and specific humidity field over Shuangliu area provided sufficient conditions for this short time heavy rainfall. Secondly, in terms of thermal conditions, Shuangliu area is in the center of the high value of false equivalent potential temperature, where θ_se reaches 80˚C and ∆θ_se500-850 reaches −10˚C. Finally, in terms of dynamic conditions, there is a rising center with an intensity of −0.7 Pa/s above Shuangliu area. The maximum vorticity of 850 hPa in Shuangliu area is 2/s, the updraft is strong, and the central value of 500 hPa is −4/s, which is the downdraft. Such configuration of positive and negative vorticity in the middle and lower troposphere leads to the release of unstable energy in the lower troposphere, and promotes the formation of heavy precipitation weather process. 3) Based on the analysis of the radio-sonde data of Wenjiang Station, the changes of K index, Sand index and uplift index in Chengdu before the precipitation indicate that the atmospheric node over Chengdu is changing from potential instability to real instability at this time. The value of the CAPE index increased dozens of times compared with that in the morning, which greatly increased the possibility of severe convective weather. At the same time, the effective potential energy of convection is much larger than the value of convective inhibition energy, which indicates that the atmospheric junction is in the true latent instability state at this time. Once a small disturbance is generated in the lower atmosphere, it is easy to break the constraint of CIN and develop into strong convection.