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Satellites show that lightning flashes about 44 times a second across the whole planet: nearly 4 million flashes a day and about 1.4 billion a year. It happens about ten times more often over land than over the oceans.

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The figure comes from NASA's Optical Transient Detector, a camera on a small satellite launched in 1995 that watched for the brief flashes of storms, day and night. In 2003 scientists used its data to estimate 44 flashes a second, well below the figure of 100 that had been quoted since 1925, when it was worked out from weather stations' records of days with thunder. Most flashes stay inside a cloud or jump between clouds; fewer reach the ground. The place with the most lightning on Earth is Lake Maracaibo in Venezuela, where storms light up the sky on 140 to 160 nights a year. A lightning channel heats the air around it to about 30,000 °C, roughly five times hotter than the surface of the Sun, and the air expands so violently that we hear the shock as thunder.

Türkçe oku
Uydu ölçümlerine göre bütün gezegende saniyede ortalama 44 şimşek çakar; bu, günde 4 milyona yakın, yılda yaklaşık 1,4 milyar şimşek demektir. Şimşek karalarda, denizlerin üzerinde olduğundan yaklaşık on kat daha sık görülür.

Bu sayı, NASA'nın 1995'te küçük bir uyduyla uzaya gönderdiği Optical Transient Detector adlı kameradan gelir. Kamera fırtınaların kısa ışık çakmalarını gece gündüz izledi. Bilim insanları 2003'te bu verilerle saniyede 44 şimşek hesapladı. Eski tahmin saniyede 100'dü; 1925'te hava istasyonlarının gök gürültüsü duyulan günlere ait kayıtlarından hesaplanmış ve o zamandan beri tekrarlanıp durmuştu. Yeni sayı bunun çok altındaydı. Şimşeklerin çoğu bulutun içinde kalır ya da bulutlar arasında çakar; yere inenler, yani yıldırımlar, daha azdır. Dünyada en çok şimşek çakan yer Venezuela'daki Maracaibo Gölü'dür; orada fırtınalar yılda 140 ile 160 gece gökyüzünü aydınlatır. Şimşek kanalı çevresindeki havayı yaklaşık 30.000 °C'ye, yani Güneş'in yüzeyinden kabaca beş kat daha sıcağa çıkarır; hava öyle ani genişler ki bu patlamayı gök gürültüsü olarak duyarız.

Sources and further reading

Background reading: Lightning
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