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Extreme Weather

All weather on Earth is powered by the Sun. As the Sun heats the Earth some parts of the planet get warmer than others. This creates differences in air pressure which gives rise to the wind. When air is heated in different places it has different characteristics. For example heating air over a desert could create a pocket of warm, dry air which could be as big as the UK! When the Sun heats the oceans it can create a giant pocket of moist, warm air. We call these pockets air masses. Air masses move around the planet as wind and bring us our weather. If the wind is blowing from the south it usually brings warm air and higher temperatures. If it’s blowing from the north it will bring cold weather. If it has passed over the ocean, it could bring moist air and give us rain.

But what is extreme weather? Read on for more!

HURRICANES

Hurricanes are also known as typhoons or cyclones, they have different names depending on where they form. Hurricanes form in the Atlantic and eastern Pacific Oceans, Typhoons in the western Pacific Ocean and Cyclones form in the Indian Ocean.

Hurricanes are single giant storms. One hurricane could cover the whole of the UK and they cause very strong winds and lots of rain. They form out at sea when a cluster of thunder storms travel over a warm patch of ocean. If the ocean is warm, it heats up the air above it, this hot air rises leaving a space behind it, (a region of low air pressure) into which more warm air is sucked. Winds which constantly circle the planet in opposite directions, called trade winds, start the storm spinning. The storm grows in size as more and more warm, moist air is sucked into the low pressure area. Once established a hurricane moves at about 13-20 kmph. It has an eye of low pressure at the centre where there is little or no wind, surrounded by winds that can reach 255kmph. Strong winds cause massive destruction but they can also increase the height of the tides too. The wind can create large waves out at sea which travel towards the land. This effect is called a storm surge and can raise the sea level by 5.5m! This causes a lot of flooding in costal regions.

If the hurricane reaches the land its supply of warm, moist air is taken away from it, the hurricane loses energy and eventually becomes just a normal storm. Most hurricanes last around two weeks.

Hurricane Katrina in August 2005 claimed the lives of at least 1836 people and destroyed 850,791 homes. The wind speed when it reached land was measured at 200 km/h however most of the damage was caused when high waves crashed over the sea defenses flooding the low lying city beyond!

LIGHTNING

Lightning has amazed mankind for generations. There are lots of ancient stories about where thunder and lightning comes from. Our word for Thursday originates from the Norse word for Thor the God of Thunder. The Norse people believed Thor threw lightning bolts from the clouds. We know now that thunder and lightning are made when the pillow like cumulonimbus clouds grow especially large and dark. This happens because the ground beneath them has been heated so much that hot air rises especially quickly. The rising water droplets in the air rub on each other and develop a static electric charge. Static electricity is what can give you a shock sometimes when getting out of a car or when walking on certain carpets. It also explains the crackly noise you sometimes hear when taking your jumper off. This crackly noise is actually miniature lightning bolts jumping around between your head and the jumper!

Clouds can develop huge static charges which when released make a spark which is many times hotter and brighter than the surface of the sun. When this super hot spark cuts through the air it heats it rapidly. The air expands very quickly leaving a sort of gap (called a vacuum) behind. When the air rushes back in to fill the gap there is a series of loud bangs or cracks. This is the thunder that you hear. Lightning is extremely hot and extremely dangerous!

Thunder and lightning are made at the same time. However you may hear the thunder after you see the lightning because light from the lightning travels much faster than the sound from the thunder. Did you know you can work out roughly how far away the lightning storm is by counting the number of seconds between the lightning and the thunder? If you divide your answer by five this is how far (in miles) the thunder storm is.