深对流系统对污染气体CO垂直动力输送作用的数值模拟研究

本文采用高分辨率WRF-Chem模式模拟了2014年7月27日和8月24日发生于长三角地区的两次强度不同的深对流系统对污染气体CO的再分布作用,对比分析了模拟的两次深对流系统在CO垂直输送过程中的差异。通过与实际雷达回波的比较发现,两次模拟的深对流发生时间、回波强度等都与实际观测接近。8月24日深对流过程发生前的对流有效位能和0～6 km垂直风切变强度均高于7月27日个例,因此 8月24日深对流系统更不稳定,发展高度更高。从CO浓度垂直剖面、质量通量随高度的变化特征发现,7月27日的深对流系统最高可以将CO输送到14 km高度处,8月24日的深对流系统最高可以将CO输送到16 km高度处。对CO浓度的垂直通量散度平均垂直廓线分析看出,7月27的深对流系统主要将CO输送到12 km附近,导致7月27日个例对流层中层的CO浓度更高,8月24日的深对流系统主要将CO输送到15 km附近,导致8月24日个例对流层上层的CO浓度更高。对垂直通量求和的分析表明,8月24日的深对流系统每小时垂直输送的CO浓度是7月27的1.3倍,而考虑到8月24日的深对流系统持续时间更长,8月24日的深对流系统对CO的垂直输送作用远远大于7月24日的深对流系统的垂直输送作用。

Numerical Simulation of Vertical Transport of Pollutant Gasesin Deep Convective System

The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) has been used to investigate the redistribution of pollutant gas CO in two deep convective systems occurred over the Yangtze River Delta on July 27 and August 24 2014, respectively. Compared with observed radar echo properties of the convection, the onset of the convection and echo intensity simulated by WRF-Chem are consistent with observations. Both the convective available potential energy and vertical wind shear between altitudes of 0 and 6 km were larger in the case of July 27 than in the case of August 24, which led to the more unstable convective system that reached higher altitude on August 24. The analysis of vertical cross sections of CO concentration and vertical mass fluxes shows that the deep convection on July 27 could transport CO to the altitude up to 14 km, whereas CO could reach up to 16 km in the case of August 24. The differences between mean profiles of CO concentration and vertical flux divergence suggested that most of the CO was transported to the altitude of about2 km, which resulted in a higher CO concentration at the middle troposphere for the case of July 27; CO was mainly transported to the altitude of 15 km for the case of August 24, which led to higher CO concentration at the upper troposphere. Analysis of vertical flux shows that deep convective transport per hour in the case of August 24 was 1.3 times greater than that in the case of 27 July. As the deep convection lasted longer in 24 August, more CO was transported in this case than in the case of July 27.