54 Earth
A storm is a bout of severe weather, with strong winds
roaring at more than 88 km/h (55 mph), lightning flashes,
thunder, and heavy rain.. HURRICANES and tornadoes
are whirling storms that can wreck whole towns.
WHAT CAUSES LIGHTNING?
Inside black thunderclouds, ice crystals and water
droplets are whirled about and clash together,
producing tiny electric charges. Positive charges
build up at the top of the cloud, negative charges
at the base. The ground below the thundercloud
is also positively charged. When the difference
between the charges gets big enough, the charge
is unleashed inside the cloud as sheet lightning,
or to the ground as forked lightning.HOW DO HURRICANES FORM?
Hurricanes form over tropical oceans in humid weather, usually in the summer
and autumn months. Warm air charged with moisture from the sea starts to
spiral upwards around a calm area called the eye. Cool air is then sucked into
the centre, taking the place of the warm air, and fuelling the storm.Also called a typhoon or cyclone, a hurricane is a powerful,
revolving storm that strikes in the tropics. It can cause great
damage when it sweeps inland.WHAT CAUSES THUNDER?
When lightning surges through the air, it instantly
heats the air to around 25,000 ̊C (45,000 ̊F). The
heated air expands and sends a shock wave through
the air, which we hear as a clap of thunder.1 TORNADOES
Tornadoes are dark, whirling columns of air that form beneath
thunderclouds. Some produce winds of up to 450 km/h (280 mph),
which can demolish houses and lift whole trains into the air.HURRICANES
4 HURRICANE FRAN
Hurricanes are so huge, they can
easily be seen from space. This
coloured satellite image shows
Hurricane Fran approaching the
North American mainland from
the Caribbean Sea in 1996.Storms
LIGHTNING STRIKES 3
Forked lightning takes the
quickest path to the ground,
often running down trees
and tall buildings.Whirling winds around the eye
may reach speeds of up to 360
km/h (200 mph)Spiral bands of rain
surround the eyeThe eye of the hurricane is a
calm area in the middle, up
to 50 km (30 miles) acrossFIND OUT MORE. Climate 62 • Rain 52 • Weather 50 • Winds 51
storms