沙尘冰核对积云起电过程影响的初步数值模拟试验

Preliminary Modelling for the Effects of Dust on the Cumulus Electrification Process

非感应起电是指云中冰相粒子间通过相互碰撞而发生的电荷转移现象,尤其以冰晶与霰粒子的碰撞过程为主,被证实是云中电荷产生的主要方式之一。沙尘作为大气冰核的重要组成成分,为了研究沙尘冰核对云中非感应起电过程的影响,本文将两种不同的非感应起电参数化方案(Takahashi方案,以下简称TAK方案;Saunders and Peck 1998方案,以下简称SP98方案)耦合至一维半云和气溶胶分档云模式中。该模式能够显性地追踪每个水成物粒子中云凝结核和冰核的质量大小,模拟每个冰核的核化过程,以及每个冰粒子的碰撞过程,从而确定霰粒子的数浓度和每个冰相粒子的电荷密度。对不同初始沙尘浓度的非感应起电过程进行了敏感性试验,模式模拟结果表明:随着沙尘粒子数浓度的增多,云中冰晶粒子与霰粒子的数浓度都分别增加,初始起电现象发生的时间提前,空间电荷密度大小增加;SP98方案和TAK方案都能模拟出1981年7月19日的一次积云观测个例的偶极型垂直分布,但SP98方案更接近实况。

Non-inductive electrification normally means charge transfer between ice particles through their collisions under a suitable environment. In particular, the collisions between ice crystals and graupel have been proven to be one of the main mechanisms of cloud charge production. As an important component of atmospheric ice nuclei, dust should play an important role in ice particle formation and cumulus cloud electrification. To study the impacts of different concentrations of dust on non-inductive electrification, two non-inductive electrification parameterization schemes（TAK scheme and SP98 scheme） were coupled into a 1.5 cloud-aerosol bin model. The prominent feature of this model is that the mass of cloud condensation nuclei and that of ice nuclei in each hydrometeor category can be determined. Simulations showed that both the charge density and the concentration of ice and graupel particles increased with increasing dust concentration, while the time of the initial electrification phenomenon advanced. Furthermore, both electrification schemes showed the dipole-type structure of the electric charges vertically as the observed distribution on 19 July 1981 for the Cooperative Convective Precipitation Experiment（CCOPE）. However, only the SP98 scheme simulated the initiation of non-inductive electrification in the developing stage of this case.