闪电通道状态变化参数化的建立及截断和再击穿的数值模拟

Establishment of a parameterization of lightning channel state changes and numerical simulation of lightning cut-off and re-breakdown

为提高数值模式对闪电精细化放电过程的仿真能力并与不断提高的闪电探测技术形成互补,探讨再击穿过程与雷暴电参数的关系,建立了一个能够再现先导截断及再击穿过程的自持电中性完整闪电参数化方案。考虑到正、负先导的极性不对称,分别设置了不同传播速度及起始和传播阈值。方案新增了通道电导率、平均电流、电荷等非线性电参数,并以这些参数的实时更新驱动闪电通道发展,通过设置不同通道状态变化阈值实现了先导通道衰退、截断以及重新激活的实时状态变化。基于通道平均电流、纵向电场以及电导率的实时变化,方案将电荷在空间重新分配,保证了通道的自持电中性。将新方案植入经典雷暴云三极电荷模型,模拟得到的云闪在通道结构、先导截断及再次激活、正负先导的极性不对称等方面与现有观测事实有较好的一致性。概念模型验证表明,新方案在保证自持电中性的前提下,在模拟包含截断和再击穿过程的完整闪电放电过程方面具有一定合理性和先进性。

To improve the simulation capability of the numerical model for the fine lightning discharge process,complement the developing lightning detection technology,and explore the relationship between re-breakdown process and thunderstorm electrical parameters,a complete lightning parameterization scheme with a self-sustained charge neutrality is established.This scheme can simulate the cut-off and re-breakdown process of leader.Considering the polarity asymmetry,different extension velocities and initiation and propagation thresholds are set for positive and negative leaders respectively.New non-linear electrical parameters such as channel conductivity,average current,and charge are added to the scheme,and real-time updates of these parameters drive the development of lightning channel while different channel state change thresholds are also set.The real-time state changing leader channels,including decay,cut-off,and reactivation process,are simulated by all the above settings.Based on real-time changes in channel average current,longitudinal E-field and conductivity,charge is redistributed in the space to ensure the self-sustained charge neutrality of channels,which is an important basis for simulating the re-breakdown process.The new scheme is employed in the classical thunderstorm cloud model with tripolar charge structure,and the simulated IC flashes are in good agreement with existing observation facts in terms of channel structure,extinguishment and reactivation of the leader,and the polarity asymmetry of positive and negative leader.The verification against observation facts and some conceptual models indicates that the scheme is reasonable and advanced in simulating the complete lightning discharge process,including extinguishment and re-breakdown process under the premise of self-sustained charge neutrality.