The first complete world map of lightning activity has been created using observations from two earth-orbiting satellites.
Central Africa, the Himalayas and parts of South America experience more lightning than anywhere else on the planet, the map reveals. In an area centred around DR Congo, there are an average of 81 lightning flashes per square kilometre per year.
The NASA map also shows that lightning very rarely occurs at sea and is almost never seen at the Earth鈥檚 poles.
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鈥淔or the first time, we鈥檝e been able to map the global distribution of lightning, noting its variation as a function of latitude, longitude and time of year,鈥� says Hugh Christian, project leader of NASA鈥檚 National Space Science and Technology Center鈥檚 lightning team.
Mountainous areas
Lightning occurs when electrical potential builds up inside clouds, in the form of turbulence between ice crystals and water droplets with either a positive and negative charge. This electrical potential is discharged in the form of lightning, which can strike the ground, pass between two clouds and occur inside the same cloud.
In central Africa, where lightning is most common, air flow from the Atlantic Ocean is enhanced by mountainous areas, causing turbulence all year round.
Steve Goodman of NASA鈥檚 Global Hydrology and Climate Center says the new data should improve scientist鈥檚 understanding of and ability to predict extreme weather system.
Lightning intensity
Two instruments were used to gather data for the aerial map. The Optical Transient detector was launched aboard NASA鈥檚 Microlab satellite in 1995 and the Lightning Imaging Sensor is fitted to a joint NASA-Japan satellite launched in 1997 to measure tropical rainfall levels.
The sensors gathered lightning data over periods of five and three years respectively.
The first lightning maps were constructed from ground-based detectors, which left many parts of the world unmapped. In 1998, the Lightning Imaging Sensor first mapped the distribution of lightning strikes in a broad region around the equator. But many parts of the globe remained uncharted. The new combined data also provides more information about the intensity, as well as the frequency, of lightning activity.