[News Landed] By Vignesh TT July 11, 2020
When we hear the word thunderstorm, the first thing that comes to our mind is the lightning bolt and the acoustic thunder that follows. These very two phenomena are the key characteristics of a thunderstorm. There are four types of thunderstorms: single-cell, multi-cell cluster, multi-cell lines, and supercell. Supercell thunderstorms are the strongest and most severe of them and are characterized by a deep and persistent rotating updraft and sometimes referred to as rotating thunderstorms.

Lightning that occurs during these thunderstorms is a commonly occurring natural phenomenon of electrical discharge during which two electrically charged regions of the atmosphere or ground equalize themselves temporarily. This causes the release of a tremendous amount of energy almost instantaneously.

Lightning can be classified primarily into three categories.

1) Intracloud (IC) – Occurs within a single thundercloud unit
2) Cloud to Cloud (CC) or Intercloud – Starts and ends in two different functional thundercloud units
3) Cloud to Ground (CG) – Primarily originates in the thundercloud and terminates on the Earth’s surface but can also occur in the reverse direction.

Cloud to Ground (CG) is less common, but it is easy to study and understand when compared to other types of lightning since it terminates on the Earth’s surface. CG can be further classified into

1)  Positive CG (+CG) – Electric charge is transferred from the Earth’s surface to thunderclouds. These accounts for less than 5% of all lightning strikes
2) Negative CG (-CG) – Electric charge is transferred from thundercloud to the Earth’s surface

Lightning characteristics and charge structures vary by the type of thunderstorm. To study these characteristics, a team of scientists from the Institute of Atmospheric Physics of the Chinese Academy of Sciences attempted to depict the lightning activity and charge structure in a supercell over North China. For this study published in Advances in Atmospheric Sciences, the scientists investigated lightning data obtained from the Beijing Lightning Network, S-band doppler radar, X-band dual-polarization radar, and ground observations.

The scientists found that the lightning frequency showed different characteristics before and after the severe hailfall associated with a supercell. +CG lightning accounted for a high percentage of CG lightning, especially during the hailfall stage. The charge structure of the thunderstorm converted from an inversion type to a normal tripolar pattern.

Graupel, hailstones, and ice crystals were the main charged particles in the convective region, while snow, ice crystals, and graupel were the main charged particles in the stratiform region.

According to Dr. Liu Dongxia, lead author of the study, lightning data can indicate a hazardous weather phenomenon, especially in places where radar detection is restricted due to mountains and buildings. In addition, lightning data can improve short term weather forecasts.