A Special Discharge Event In Thunderstorms

Compact intracloud discharge (CID) is a very special discharge event produced in thunderstorms. On the basis of large amount of CIDs recorded by VLF/LF lightning location networks in Guangzhou and Chongqing, multiple characteristics of CIDs that are different from regular intracloud and cloud-to-ground lightnings are analyzed. Differences between +CIDs and–CIDs are investigated in many respects, and it is found that many of their characteristics are distinctly different from each other and–CIDs show more special features. There are conclusions in following respects:CIDs produce very large electric field changes, which are generally larger than that produced by return strokes. Compared with +CIDs,–CIDs generally produce larger electric field changes, which are 1.4 times of that produced by +CIDs on average in this paper. CIDs are usually isolated with other discharge processes, which means that CIDs rarely follow other discharge processes. However, some portion of CIDs can be the initiation processes of regular discharge processes, and for such situation, +CIDs have much higher possibility than–CIDs.Low frequency radiation signals produced by CIDs can be reflected between the ground and the ionosphere and can produce ionospheric reflection pairs. Using the time differences between the reflection signals and the original signals of CIDs, a new method for determining 3D locations of CIDs are developed in this paper. This method can accurately determine 3D locations of CIDs in a large area. It is especially useful for computing discharge heights of CIDs. With this method, discharge heights of large amount of both polarities of CIDs are computed, and it is found that +CIDs mainly occur at the height of 7-15km while–CIDs mainly occur at the height of 15-18km.There are certain relationships between CIDs and convective strength. CID rate generally increases with convective strength. Thunderstorms usually produce much more +CIDs than–CIDs, but the percentage of–CIDs increases as the convective strength increases. A rare thunderstorm producing large amount of–CIDs is further analyzed and compared with a common one predominated by +CIDs. It is found that the thunderstorm producing large amount of–CIDs is significantly more vigorous. Radar observations show that the cloud top is persistently higher than 15km, and sometimes even as high as 20km.Multiple differences between +CIDs and–CIDs are comprehensively analyzed at last, and –CID is considered to be a more special type of discharge.