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Abstract
The effects of thermodynamic and moisture factors on cloud-to-ground (CG) lightning polarity in the warm season were discussed. Small convective available potential energy (CAPE) represents relatively shallow convection, which is beneficial to the generation of positive lightning. Large vertical wind shear results in the displacement of upper-level positive ice crystals and promotes the initiation of +CG lightning from positive ice crystals. The dry low- to midlevel troposphere and the high cloud base in the plateau region favor +CG lightning, while the strong thermodynamic conditions in the basin region offset the influence of these moisture factors. In the plateau region, due to the limited cloud thickness, high total column liquid water may mean high cloud water content in the warm cloud region rather than high liquid water content in the mixed-phase region, which is unfavorable for the middle-level positive graupel and thus is unfavorable for the initiation of +CG lightning. In the basin region, the cloud thickness is relatively thicker, the high total column liquid water means that the liquid water content in the warm cloud and the mixed-phase region is both high, which is conducive to the middle-level positive graupel and the +CG lightning.
Highlights
The local thermal, dynamic, and microphysical conditions affect the polarity of cloud-to-ground (CG) lightning by synergistically affecting the structure of the thunderstorm and the processes of electrification and discharging [1,2,3,4,5,6,7].Lightning polarity depends on the vertical charge distribution of the thunderstorm [8,9,10,11,12,13]
Kalb [24] suggested that equivalent potential temperature, convective available potential energy (CAPE), mean relative humidity, precipitable water, freezing level, and vertical wind shear did not have a significant effect on +CG lightning, while the lower cloud base heights and warm cloud depth and higher dew points were conducive to the occurrence of +CG lightning in the central United States
This study focuses on discussing the dependence of lightning polarity on thermodynamic and moisture factors in this complex topography and comparing the similarities and differences between the dependence in the plateau region and the basin region
Summary
The local thermal, dynamic, and microphysical conditions affect the polarity of cloud-to-ground (CG) lightning by synergistically affecting the structure of the thunderstorm and the processes of electrification and discharging [1,2,3,4,5,6,7]. The normal charge structure is that the upper level of the thunderstorm is a positive charge zone, the lower part is a negative charge zone, and the discharge process transfers the negative charge to the ground and forms a –CG lightning flash. The discharge process transports the positive charge to the ground and forms a +CG lightning flash. The physical factors controlling the polarity of lightning are not very evident, the meteorological environment still partly explains the electrification, charge structure, and the generation of +CG and –CG lightning through regional differences.
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