BBC Broadcast Meteorologist, Helen Young, explains a few of the famous winds experienced around the World.
Wind is the result of air moving from one point to another. Air moves due to differences in temperature and pressure.
At the equator hot air rises and moves out towards the poles, gradually cooling. It eventually sinks back down to the earth's surface. This cooler air is then forced to flow back to the equator to replace the hot air that is rising. This is an over simplification but around the world cells of circulating air are set up helping to create our winds.
Ancient mariners were very aware of these winds. Winds carried traders to the Americas from Europe; they are now known as 'Trade winds'. On the equator there is little wind, mariners called this region the doldrums (after an old English word meaning dull) because they feared being stranded there.
Air can move in different directions and at different speeds so wind is always described as a vector with direction given in degrees and speed usually in mph. Gusts of wind are also usually reported. A gust of wind usually only lasts from a few seconds to a few minutes. The strongest gust of wind ever reported on earth was at Mount Washington in New Hampshire on 12th April 1934. 231mph was reported, caused by air being funnelled between the top of the mountain and the troposphere, (the region of the atmosphere where all our weather takes place). In simple terms the air was forced through the gap.
Normally the strongest winds occur about 10-12km (30,000-35,000ft) above the earth's surface. They occur where cold air from the poles meets hot air from the equator. They are called jet streams and like a conveyor belt transport air rapidly from one place to another right around the earth. The winds in the centre of the jet stream can be as much as 250mph. They sometimes help strengthen and steer areas of low pressure and are therefore very important to weather forecasters as well as airline pilots!
The strongest winds at the surface of the earth are associated with tornadoes, the most violent storms on earth. Wind speeds can be up to 300mph. Hurricanes aren't far behind in terms of strength. They are the largest storms on earth with winds sometimes as high as 200mph. In Japan winds associated with these large storms were given the name Kamikaze (Divine or God winds).
Obviously World War two brought new meaning to this word. The monsoon winds are not as strong but affect a vast area. They are most commonly associated with South Asia. The south-westerly monsoon winds bring copious amounts of rain from June onwards. During the winter months the winds turn North-easterly and South Asia is mainly dry.
There are also very localised, small scale winds, for example, sea breezes. These occur in summer when hot air rises over the land and is replaced by cooler air from the sea. On a hot day sea breezes can bring refreshingly cooler conditions to coastal resorts.
Sometimes localised winds have been given names by the people who live where these winds blow, especially it would seem in desert or mountainous regions.
In mountainous areas winds are either forced over mountains or through them. If the wind is forced over them on the leeward side of the mountain the air sinks, creating an area of high pressure and clear skies. Because the air on this side of the mountain is compressed it also raised the temperature, resulting in a warm wind. This type of effect can be seen over the Scottish Mountains and the Pennines but on a far grander scale to the east of the Rockies in the USA. Here the wind is called the Chinook. This is a red Indian word meaning snow eater and as it is a warm wind it certainly does help to melt the snow! In the Swiss Alps this type of wind is called a Fohn wind.
When the wind is forced through the valleys in mountainous regions the mountain chain acts as a funnel and therefore the wind becomes stronger. The Mistral is the name given to this type of wind that blows through the Rhone Valley between the Alps and Cevenes. The wind can reach up to 93mph. The residents of the French Riviera and the Gulf of Lyon at the end of the Rhone Valley take the full brunt of this cold, strong wind.
Other winds result from intense heating of inland areas which creates an area of low pressure. The Sirocco brings hot, dry, dust laden winds to the Mediterranean from the Sahara. If the conditions are right these winds move across the Mediterranean pick up moisture from the sea and by the time it reaches Europe it brings warm, humid air and low cloud. The Khamsin is a similar wind which blows from Egypt into the Eastern Mediterranean. It is a dust laden wind which devastates crops and is feared by the locals. The Shamal is a north-westerly wind which blows down the Gulf states whipping up the sand and reducing the visibility to a few 100 metres.
There are also cold winds. Cold air is dense and so moves down mountain sides creating what is call katabatic (Greek word to mean go down) winds. A good example is the Bora wind which is a cold north-easterly wind which blows in winter down the east coast of the Adriatic from the Balkan mountains. At it's most intense it can reach 115mph. The most extreme type of katabatic wind is found in the Antarctic where cold gusts of wind surge across the polar ice caps. They can reach 120mph! Chilly for the penguins!
All these winds affect lives across the world today; but in the words of Donald Pealtie (American author and biologist) 1898-1964 "the wind is the oldest voice in the world"!
Other features in the Climate Zones series:
- Forecasters Biography: Helen Young
- Different types of wind
