Review on Inverted Charge Structure of Severe Storms

The charge structure in storms is regarded as a bridge linking lightning activity with dynamic and microphysical conditions. An inverted charge structure is always seen in severe storms, which attracts much attention in recent years.Although the charge structure in thundercloud is complicated, the tripole charge structure could be used to describe the main discharging region. In general, the tripole charge structure is characterized by a negative charge region between levels of -10 ℃ and -25 ℃, accompanied by a respective positive charge region below and above the negative charge region. In 2000, lightning mapping array and electric field sounding are carried out in the experiment of Severe Thunderstorm Electrification and Precipitation Study (STEPS) organized by USA. Most case studies in this experiment indicate that the charge structure in severe storms is opposite to the normal charge structure, when original positive charge changes into negative charge, and vice versa. This new structure is called inverted charge structure.Related studies on the inverted charge structure are reviewed, focusing on the discovery, formation, relevant numerical simulation and the detection method. The inverted charge structure appears in the severe storms, resulting in the substantial positive cloud-to-ground lightning. Moreover, it is always associated with disastrous weather. The inverted charge structure doesn't appear in the beginning of storms, but in the special developing stage of storms.The inverted charge structure formation is associated with the strong ascending motion in severe storms, which makes the liquid water content change and influences the electrification process during the collision among different kinds of particles in the main electrification region. It will result in graupel charged positively and ice crystal charged negatively, implying the formation of the inverted charge structure. One view focuses on microphysical conditions, by which the charge separation is influenced during the collision of particles, and this physical process is defined as microphysically-inverted. Another view is, the inverted charge structure could be formed through the dynamic transport and wind shear in severe storms when the graupel is still charged negatively in the main electrification region, and this is defined as dynamically-inverted. The research on the latter is relatively scarce compared to the former.