Lightning (Electrical Storm)
Primary reference(s)
WMO, 2017. International Cloud Atlas: Lightening. World Meteorological Organization (WMO). Accessed 26 November 2019.
Additional scientific description
Lightning is a transient, high-current electric discharge with pathlengths measured in kilometres. The most common source of lightning is the electric charge separated in ordinary thunderstorm clouds. Well over half of all lightning discharges occur within the thunderstorm cloud and are called intracloud discharges (AMS, 2012).
Lightning is a large electrical discharge caused by a thundercloud. It can occur within a cloud as intracloud lightning, between clouds as intercloud lightning, or between the cloud and the earth as cloud-to-ground lightning. A lightning discharge consists of pulses of electric current carried by electrons. The current is driven by a high voltage between the cloud’s charge centres or between them and the earth. During the development of a thundercloud, negative charge is accumulated in the hail-forming region at the central part of the cloud, and positive charge in the top region which consists of ice crystals (Finnish Meteorological Institute, 2019).
Lightning strikes are classified into different types according to their own characteristics. The two most common types are cloud-to-ground lightning and cloud-to-cloud lightning (WMO, 2017).
- Cloud-to-ground lightning is lightning discharge between a cumulonimbus cloud and the ground. Of all types of lightning, cloud-to-ground lightning poses the greatest threat to people and facilities on the ground (WMO, 2017). The usual cloudto- ground lightning has been studied more extensively than other lightning forms because of its practical interest (i.e., as a cause of injury and death, disturbances in power and communication systems, and ignition of forest fires) and because lightning channels below cloud level are more easily photographed and studied with optical instruments (AMS, 2012). Cloud-to-ground lightning can occur as either positively or negatively charged bolts. Positively charged bolts are considerably more rare, more powerful (e.g., by an order of magnitude or more) and often can strike miles beyond the parent anvil of the thunderstorm (e.g., these positive strikes are referred to as a ‘bolt out of the blue’) (NOAA, 2019).
- Cloud-to-cloud lightning and cloud-to-air discharges are less common than intracloud or cloud-to-ground lightning. All discharges other than cloud-to-ground are often lumped together and called cloud discharges (AMS, 2012; WMO, 2017). Cloud-to-cloud lightning is the discharge between areas of cloud without the discharge channel reaching the ground. For most of the time, it occurs between oppositely charged portions of the same cloud but sometimes it takes place between two separate clouds. Since the discharge channel of cloud-to-cloud lightning may be obscured by the cloud, it may or may not be visible to an observer on the ground. It may therefore be surprising to learn that cloud-to-cloud lightning is, in fact, the most frequently occurring type of lightning. It occurs around ten times more often than cloud-to-ground lightning. Cloud-to-cloud lightning does not pose a threat to life and property on the ground. However, this type of lightning takes place in the sky and sometimes passes through the clear air between clouds, it is therefore of great practical interest to those concerned with the safety of aircraft (WMO, 2017).
Ball lightening includes a fireball which sometimes appears after a lightning flash. Its diameter is usually between 10 and 20 cm and rarely attains 1 m. The fireball moves slowly through the air or along the ground, it may be distorted in passing through narrow places and usually vanishes suddenly with a violent explosion (WMO, 1992).
Metrics and numeric limits
Not available.
Key relevant UN convention / multilateral treaty
Not available.
Examples of drivers, outcomes and risk management
Lightning strikes the earth more than 8 million times per day. The risk of being struck is low but the consequences of lightning strike injuries are serious. During 2003–2012, lightning caused an average of 35 deaths per year in the United States (CDC, no date). The Centres for Disease Control and Prevention also provides helpful fact sheets on lightning safety tips, first aid recommendations, lightning strike victim data, information for workers, information for outdoor recreation, information for organised sporting events, information for water activities, and information for pet owners (CDC, 2020).
As an example of a National Alerting Parameters, the China Meteorological Administration (2012) has three alerting thresholds and related preventative measures, Including:
- Yellow: “In 6 hours, there will be thunder & lightning and likely to cause disasters.”
- Orange: “In 2 hours, the thunder & lightning is either occurring or will occur with a high likelihood, and it’s quite possible to cause disasters or accidents.”
- Red: “In 2 hours, the thunder & lightning is either occurring or will occur with a highest likelihood; it’s extreme possible to cause disasters or accidents.”
References
AMS, 2012. Lightning. American Meteorological Society (AMS), Glossary of Meteorology. Accessed 25 November 2019.
CDC, no date. Lightning. Centres for Disease Control and Prevention (CDC). Accessed 8 October 2020.
CDC, 2020. Lightning: Lightning Safety Tips. Centres for Disease Control (CDC). Accessed 23 March 2021.
China Meteorological Administration, 2012. Weather Warnings: Lightning. Accessed 25 November 2019.
Finnish Meteorological Institute, 2019. Lightning and thunderstorm. Accessed 25 November 2019.
NOAA, 2019. The Positive and Negative Side of Lightning. National Oceanic and Atmospheric Administration (NOAA). Accessed 25 November 2019.
WMO, 1992. International Meteorological Vocabulary. 2nd Edition. World Meteorological Organization (WMO). Accessed 19 November 2020.
WMO, 2017. Lightening: Cloud Discharge. World Meteorological Organization (WMO). Accessed 23 March 2021.