NASA Marshall Space Flight Center
Although lightning and thunderstorm activity is waning now in the US, things are beginning to heat up in the tropics. This map was produced for the autumn of 1999 and shows the global distribution of lightning as detected from the Optical Transient Detector (OTD) launched from a Pegasus rocket in 1995. The OTD is capable of monitoring both daytime and nighttime lightning and was developed at Marshall Space Flight Center in Huntsville, Alabama. Measurements from the OTD have revealed that the global flash rate is approximately 40 flashes per second. It's estimated that over 1.2 billlion lightning flashes (both cloud to ground and cloud to cloud) occur around the world every year. Most of these flashes are observed in the intertropical convergence zone (ITCZ). The ITCZ is a discontinuous band of convective clouds and thunderstorms that parallel the equator and marks the area where the trade winds of the Northern and Southern Hemisphere converge - it shifts with the seasons. In the fall of 1999, the Amazon Basin of South America, the Mediterranean Sea, the Congo Basin of Africa, southeast Asia and Indonesia was where most of the lightning flashes were observed. By December, the focus of the activity shifts slightly southward, toward south central Africa and northern Australia.
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