Lightning
A bolt of cloud-to-ground lightning strikes the Mediterranean Sea off of Port-la-Nouvelle in southern France. This specific event illustrates one of three primary forms that scientists distinguish by location. Intra-cloud lightning occurs within a single thundercloud, while cloud-to-cloud lightning happens between two separate clouds. Cloud-to-ground lightning is the type that terminates on the ground and is referred to as a lightning strike.
Most lightning events are intra-cloud or cloud-to-cloud flashes, yet these types indirectly affect humans through their influence on atmospheric chemistry. The most direct effects on human life come from cloud-to-ground lightning because it actually hits physical objects. Positive versus negative cloud-to-ground flashes have different physical characteristics that researchers can measure. Negative lightning transfers electrons downward to the ground along the channel, whereas positive lightning transfers charge upward.
Positive lightning makes up less than 5% of all lightning strikes but creates much more intense currents. An average negative bolt carries 30 kiloamperes of current, transferring about 15 coulombs of charge. Large positive bolts can create peak currents up to 400 kiloamperes and transfer several hundred coulombs. These powerful positive strikes heat surfaces to higher levels, increasing the likelihood of fire ignition.
The main charging area in a thunderstorm occurs in the central part of the storm where air moves upward rapidly. Temperatures in this zone range from minus 10 degrees Celsius to minus 20 degrees Celsius. This combination of temperature and rapid upward movement produces super-cooled cloud droplets, small ice crystals, and graupel. Graupel is soft hail that is considerably larger and denser than the other particles.
When rising ice crystals collide with falling graupel, the ice crystals become positively charged while the graupel becomes negatively charged. The updraft carries the positively charged ice crystals upward toward the top of the storm cloud. The larger graupel falls or remains suspended in the middle of the thunderstorm cloud. This process results in the upper part of the cloud becoming positively charged and the lower part becoming negatively charged.
Scientists call this mechanism non-inductive charging because it relies on particle collisions rather than external electric fields. Some theories suggest that aqueous hydrogen ions and hydroxide ions carry the charge in liquid water. Other researchers propose that uncharged colliding water drops can become charged through transfer between them in an existing electric field. William Thomson demonstrated charge separation in pure liquid water as early as the 1840s.
A bidirectional channel of ionized air called a leader initiates between oppositely-charged regions inside a thundercloud. Negative leaders travel downward toward Earth while positive leaders move upward within the cloud. These leaders often split into branches resembling a tree-like pattern during propagation. About 90% of ionic channel lengths between pools are approximately 50 meters long.
When a stepped leader approaches the ground, grounded objects like trees and tall buildings develop upward streamers. A negative leader connects to an available upward streamer in a process called attachment. Once connected, electrons accelerate rapidly across the entire leader network at one-third the speed of light. This massive surge is known as the return stroke and represents the most luminous part of the discharge.
The core temperature of plasma during the return stroke may exceed 30,000 degrees Celsius. The nearly instantaneous heating causes air to expand explosively, producing a powerful shock wave heard as thunder. High-speed videos show that most negative cloud-to-ground flashes contain three or four individual strokes, though some flashes have up to thirty strokes. Each re-strike occurs about 40 to 50 milliseconds after the previous one.
Lightning on Earth occurs at an average frequency of approximately 44 times per second, equating to nearly 1.4 billion flashes annually. About 70% of these strikes happen over land in tropical regions where atmospheric convection is strongest. The place on Earth where lightning occurs most often is Lake Maracaibo, which produces 250 bolts daily on average.
This activity near Lake Maracaibo happens on 297 days each year through the Catatumbo phenomenon. The second highest lightning density exists near Kifuka village in the Democratic Republic of Congo mountains. Other hotspots include Singapore and Lightning Alley in Central Florida. In the tropics, only 10% of lightning flashes are cloud-to-ground because the freezing level sits higher in the atmosphere.
At Norway's latitude around 60 degrees North, half of all lightning is cloud-to-ground since the freezing elevation is lower there. Researchers found final speeds of ten observed flashes ranged from 1.0 to 1.4 meters per second with an average of 4.4 meters per second. An unusually long bolt measuring 829 kilometers occurred across Texas and Kansas in October 2017.
Each lightning flash in temperate and sub-tropical areas produces 7 kilograms of ozone on average. This process leads to significant local increases in both ozone and oxides of nitrogen within the atmosphere. Lightning serves an important role in the nitrogen cycle by oxidizing diatomic nitrogen into nitrates deposited by rain.
These nitrates fertilize plant growth and support other organisms throughout ecosystems. The very high temperatures generated break apart nitrogen and oxygen molecules in the air. This creates reactive hydroxyl radicals that initiate chemical reactions breaking down greenhouse gases like methane. Lightning is the major natural cause of wildfire, estimated to cause 10% of forest fires worldwide.
Wildfires contribute to climate change by emitting greenhouse gases and affecting vegetation cover. Multiple studies suggest there could be an increase in Boreal and Arctic lightning-ignited fires due to changing climate patterns. The ratio of Arctic summertime lightning strikes increased from 2010 to 2020 compared to total global strikes.
The earliest detector invented to warn of thunderstorms was the lightning bell installed by Benjamin Franklin in his house. Andrew Gordon created the electric chimes device in 1742 which formed the basis for these early warnings. Modern systems use electromagnetic pulses transmitted by lightning strikes that propagate within the Earth-ionosphere waveguide.
The United States federal government constructed a nationwide grid of lightning detectors allowing real-time tracking across the continental U.S. The EUCLID detection network combines several national networks across Europe. Blitzortung operates over 500 detection stations owned by hobbyists and volunteers globally. The World Wide Lightning Location Network functions as an academic-led system while Vaisala GLD360 serves private enterprise needs.
Satellite instruments began observing lightning distribution in the late 1970s. NASA launched the Optical Transient Detector aboard OrbView-1 on the 3rd of April 1995. NOAA started launching Geostationary Operational Environmental Satellites with Geostationary Lightning Mapper instruments beginning in 2016. EUMETSAT launched the Lightning Imager on Meteosat Third Generation at the end of 2022.
The first known photograph of lightning dates from 1847 and was taken by Thomas Martin Easterly. William Nicholson Jennings captured the first surviving photograph in 1882. Many cultures viewed lightning as a sign or part of a deity including Greek god Zeus and Aztec god Tlaloc.
Norse mythology features Thor while Finnish tradition honors Ukko. Hindu culture recognizes Indra and Yoruba religion worships Sango. Ancient Etruscans produced guides to divining the future based on thunder omens called ceraunoscopy. In Jewish, Islamic, and Christian scriptures, lightning holds supernatural importance.
Political parties have used lightning flashes as symbols of power since the 1930s. The People's Action Party in Singapore adopted the symbol while the British Union of Fascists used it during that decade. The Schutzstaffel paramilitary wing of the Nazi Party incorporated the Sig rune into their logo. German Blitzkrieg meant lightning war and served as a major offensive strategy during World War II.
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Common questions
What is the average frequency of lightning strikes on Earth per second?
Lightning occurs at an average frequency of approximately 44 times per second. This equates to nearly 1.4 billion flashes annually across the globe.
Where does lightning occur most often on Earth and how many bolts happen daily there?
The place on Earth where lightning occurs most often is Lake Maracaibo which produces 250 bolts daily on average. This activity near Lake Maracaibo happens on 297 days each year through the Catatumbo phenomenon.
When was the first known photograph of lightning taken and by whom?
The first known photograph of lightning dates from 1847 and was taken by Thomas Martin Easterly. William Nicholson Jennings captured the first surviving photograph in 1882.
How much ozone does a single lightning flash produce in temperate areas?
Each lightning flash in temperate and sub-tropical areas produces 7 kilograms of ozone on average. This process leads to significant local increases in both ozone and oxides of nitrogen within the atmosphere.
Which historical figure created the electric chimes device for thunderstorm warnings in 1742?
Andrew Gordon created the electric chimes device in 1742 which formed the basis for early thunderstorm warning systems. The earliest detector invented to warn of thunderstorms was the lightning bell installed by Benjamin Franklin in his house.