Effects Of Convection Strength On The Charge Structure And Lightning Discharge In A Thunderstorm Cell

There are large differences in the charge structure and lightning discharge characteristics within the different types and different strength thunderstorms and complex reasons for their formation. In order to discuss that whether the convection strength has an important effect on the charge structure and lightning discharge characteristics, and give a reasonable explanation for the cause of the formation of the charge structure and lightning discharge and the relationship between them. A three-dimensional dynamics-electrification coupled cloud model was used to investigate the relationship between the charge structure and lightning discharge and convection strength of a thunderstorm cell, by changing the potential temperature in the center of disturbance region and conducting sensitivity tests. Results show that the convection strength of the thunderstorm cell increases with the potential temperature disturbance and affects the spatial charge structure and lightning discharge, but there is always a lower positive charge region. When the convection is weak,the charge structure within the thunderstorm is simple,comprising only a main negative charge region and lower positive charge region,without a upper main positive charge region, and only occurs the reverse polarity intracloud lightning. In the medium-intensity convection thunderstorm, the charge basically presents the normal tripole structure, the main negative area has upper and lower two charge centers, and the upper center of charge density is larger. In the tripole structure, there exist both the reverse polarity intracloud lightning and normal polarity intracloud lightning. And the negative cloud-to-ground (-CG) flashes are triggered between the lower positive and main negative charge regions, and two +CG flashes occur between the main negative and main positive charge regions, with positive leaders spreading downward through the main negative charge region and bypassing the lower positive charge region and eventually developing to the ground. In addition to the main negative charge, upper main positive charge and lower positive charge regions in the strong thunderstorm cell, there is a small-range weak negative charge region under the lower positive charge region and a negative screening layer on top of the cloud. The charge structure is relatively complex, having five vertically stacked regions of charge with alternating polarity. In the most complex stage of charge structure, there are the -CG flashes starting between the negative charge region at cloud base and lower positive charge region. The structure is mainly due to the upper main positive charge region with longer duration and higher charge density increasing the attraction to free negative charge in the surrounding atmosphere, and forming the negative screening charge layer at the cloud top. Meanwhile, owing to the strong convection, graupel particles grow more rapidly, solid precipitation increases, and a short-lived weak negative charge region beneath the lower positive charge region is formed by graupel in the downdraft through the inductive collision with cloud droplets.