twice. However, it only needs to strike once to cause serious damage, injury or death
Lightning does not strike
StrikeONE
THERE are, on average, about 1,800 thunderstorms in progress at any one time around the world with 100 lightning strikes every second. A lightning bolt travels at about 14,000mph and heats up the air around it to 30,000°C - five times hotter than the surface of the sun. The chance of being hit by lightning is about one in three million.
Lightning is dangerous. Currently,
between 30 and 60 people are struck by lightning each year in Britain of whom, on average, three may be killed. This compares with about 75 deaths in the much larger USA. The number of people killed by lightning each year has varied markedly. For example, the worst year in recent decades was 1982 when 14 people were killed, whereas there were no deaths in 2000 or 2001 - the first years without lightning fatalities since 1937.
There are around 300,000 ground
strikes by lightning every year in Britain. On average (based on a ten-year period), this means that someone is struck once every 6,000 strikes and someone killed once every 100,000 strikes. A ‘thunderstorm day’ may produce up to 10,000 ground strikes although the exceptional day of 24 July 1994 produced 85,000 ground strikes.
What causes thunderstorms and what should you do to protect yourself during one?
Thunderstorm formation Thunderstorms can form when moist, unstable air is lifted vertically into the atmosphere. This lifting can occur by:
(1) Convective lifting When there is unequal warming of the surface of the earth and the atmosphere is unstable, parcels of air can be lifted rapidly into the atmosphere forming isolated thunderstorm cells. These storms are usually localised and while they can be severe, their life span may be as short as 15 minutes. (Figure 1)
(2) Orographic lifting Warm moist air is forced up against the side of a mountain or range of mountains in unstable atmospheric conditions. (Figure 2)
(3) Frontal Lifting Warmer air is uplifted at the leading edge of a frontal system. (Figure 3) Immediately after lifting begins, the rising parcel of warm moist air begins to cool due to adiabatic expansion. At a certain elevation the dew point is
By PETER HOLLINGSWORTH
Figure 1: Formation of a convective thunderstorm
Figure 2: Formation of an orographic thunderstorm Figure 3: Formation of a frontal thunderstorm
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