云凝结核浓度对南京地区一次冰雹云过程影响的数值研究

采用WRF模式与包含了云凝结核(Cloud Condensation Nuclei,CCN)浓度和霰雹密度预报的NSSL(National Severe Storm Laboratory,国家强风暴实验室)微物理方案,模拟不同CCN初始浓度条件下南京地区的一次冰雹云过程,分析不同CCN初始浓度影响下冰雹云过程的宏微观演变特征,以及对流发展不同阶段的水凝物粒子及流场、温度场的垂直分布特征。研究发现:1)较大的CCN初始浓度虽然抑制了前期对流降水,但对后期对流降水的产生有促进作用;2)CCN初始浓度的增加使得模拟雷达回波的强回波区域(大于40 dBz)缩小,中等强度区域(小于40 dBz)扩张。3)CCN初始浓度增大不利于对流发展初期云雨自动转化过程的发生,但是促进了冰晶与雪的产生,使得冰雹含量峰值出现的时间推迟。4)CCN浓度增大抑制了雨水产生,间接使得霰粒子更倾向于干增长,平均密度更小;5)较大的CCN浓度促使冰雹云单体的发展时间增长。

Numerical simulation of the influence of cloud condensation nucleus concentration on a hail cloud in the Nanjing area

In this study,based on the results of WRF model simulation with an NSSL microphysical scheme,which included prediction of cloud condensation nuclei(CCN) concentration and volume of graupel in hail,a hail storm that developed in Nanjing was simulated,and three different CCN initial concentrations were used.The variation of precipitation and hydrometeor,as well as the vertical distribution of the hydrometeor,temperature and wind at different stages of the storm''s development,were investigated.The results revealed the following:1)Greater CCN concentration decreases the precipitation during the early stage,yet increases the precipitation during the later stage.2)Greater CCN concentration leads to the enlargement of the high dBZ area(>40 dBz) and the atrophy of the middle dBz area(<40 dBz).3)Greater CCN concentration increases the amount of snow and ice,decreases the graupel,and delays the appearance of the high peak of the hail amount.4)Increased concentration of CCN inhibits rain production,indirectly rendering the helium particles more prone to dry growth,with a lower average density.5)Greater CCN concentration suppresses an early warm cloud process,but promotes the production of snow and ice,which causes the hail storm to be stronger and last for a longer period of time.