Simulation of Charge Structure Formation in Stratiform Regions of Mesoscale Convective System

This study uses an electrification and discharge model to simulate the charge structure formation in stratiform regions of a mesoscale convective system (MCS). Two non-inductive electrification schemes are used based on liquid water content (LWC) and graupel rime accretion rate (RAR). Snow plays an important role in the formation of charge structure in the stratiform region. The charge carried by snow is mainly converted from ice crystals.

The simulation results of the two non-inductive electrification schemes show that the stratiform and convective regions of the MCS show different charge structures. From the convective region to the stratiform region, the main negative charge layer has a significant tilt — the height of the main negative charge layer in the stratiform region (-30--20°C) is higher than that in the convective region. A negative dipole charge structure, with a negative charge layer by graupel above a positive charge layer by snow, thus appears in the stratiform region of the MCS. There may be a thin layer of positive charge above the main negative charge layer in the stratiform region under the TGZ scheme. When ice crystals are converted into snow in the stratiform region, the positive charge carried by the ice crystals is also carried over to the snow. As sedimentation of snow is easier than that of ice crystals, the positive charge layer consisting of snow crystals is located at a relatively low height. Although many studies have recognized the role of snow in the formation of charge structures in the stratiform regions of MCSs, there is no direct evidence for the source of charge for snow crystals. This study provides a new explanation for the origin of snow charge in stratiform regions.

The source of charge in the stratiform cloud region is also discussed based on sensitivity experiments accompanying by the melting electrification mechanism.