Lecture 32: Lightning - Causes, Effects, and Safety, Study notes of Meteorology

Download Lecture 32: Lightning - Causes, Effects, and Safety and more Study notes Meteorology in PDF only on Docsity! 4/1/2008 1 MET4300 Lecture 32 Lightning 7 April 2008 Lightning Effects • Cause many forest fires • Damage buildings and  start structure fires • Kill ~75 people a year  (US)  • Injure about 8 x as many,  – But official reports  indicate 2.5 injuries per  death – One reported injury per  114,000 strikes Earth’s Fair Weather Field Maintained by Thunderstorms Book’s View of TR Electrical Structure Charge Separation Interface Induction 4/1/2008 2 Lightning Flash • 100 Flashes/s worldwide • Initiates when the field  exceeds 1‐3 x 106 V/m • Peak current is 15000 to  30000 Amperes  • Conducting channel is 2‐3 cm  in diameter • And is typically 5 km long • Peak temperature is 15000‐ 30000 K • Total charge transferred is 3‐ 30 Coulombs  • A flash may be composed of  1‐30 strokes; 3‐5 is typical Lightning Flash Another View Remember a Flash may comprise many Strokes Branching occurs in the stepped leader and initial return stroke Kinds of Lightning In Cloud Cloud to Cloud Cloud to Ground Only 20% are Cloud to Ground