When is it going to stop raining? Why is it so hot, we’re in the season of winter? How is our weather predicted? Where have these winds come from?
Meteorologists claim that unseasonable temperatures are caused by changing weather patterns over the oceans. Instead of cold air being drawn down from the north, as usually happens in winter, for example, warm air continues to flow in from the south and west. The earth’s atmosphere is a constantly swirling sea of air currents whose flow, temperature, moisture and concentration are ruled by a complicated interaction between the air and the oceans.
The jet stream is a river of fast flowing air at high altitudes above the earth that generally flows from west to east over the mid-latitudes. I don’t know why they are called “streams” because at the rate they travel they are more similar to rapids. However if you imagine a fast flowing river with large rocks and stones placed in specific areas, then you can imagine ripples and waves will occur as the river’s water splashes against them; When these ripples and waves get big enough, the water there may become rather tumultuous. Liken this to airplanes and you have turbulence. Well this is similar to the jet stream.
The jet stream flows in the same direction as which the earth rotates. This strong current of air pushes weather systems around the world, and greatly affects local weather patterns by impelling them forward.
These winds steer storms and help establish where the areas of high and low air pressure at the Earth’s surface.
In our latitude the jet stream is generally found at around 35,000 feet and is called the Polar Front Jet Stream. The polar jet stream, as its name suggests, divides the cold polar air to the north and the warm sub-tropical air to the south.
In October 1987, hurricane force winds caused devastation across south-east England (UK), killing 13 people and causing over 1.2 billion of damage and a fall of an estimated 15 million trees. In this example a jet stream caused an extreme rapid drop in surface pressure within depression, therefore tightening isobars and creating these damaging winds.
The position and intensity of jet streams is a meteorological parameter for forecasting severe weather conditions. In winter, the jet stream over the Atlantic sometimes divides, with one part flowing high over Arctic regions, and one part plunging south towards the Mediterranean. Such conditions in the upper atmosphere can pioneer for severe winter weather in the UK, resulting in Arctic or Siberian winds, sub-zero temperatures and blizzards.
Further afield, in the United States, a powerful jet stream, often in spring, is an important element in the development of in the development of highly organized and long lasting thunderstorms, known as super cells. These storms can help to produce the sometimes sadistic tornadoes of the Great Plains and are the cause of approximately 90% of storm damages reported.
By looking at a diagram of a jet stream it is possible to pick out the areas below which a depression or anticyclone is most likely to form. This used to be done by meteorologists studying hard looking at maps; it is now done by a computer.
No single occurrence can be attributed to climate change. However you can be sure that the position of the jet stream gives a clear indication of severe weather events.
Sources
http://www.bbc.co.uk/weather/features/understanding/jetstreams_uk.shtml
http://www.weatheranswer.com/public/Jet_Stream_by_Krista_Feierabend
http://www.pbs.org/wgbh/nova/vanished/jetstr_faq.html
ttp://www.meteogroup.co.uk/uk/home/weather/weather_news
