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Buys-Ballot Law, weather jet streams, and the relationship between Pressure and Wind.

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Wind at your Back Low to the Left

How are weather jet streams formed? What do jet streams have to do with our weather forecasts? As you might suspect, wind in the upper atmosphere must have some effect on ground-level winds.  What do airport wind socks detect?

The connection between pressure, temperature and jet streams comes from the Buys-Ballot law, which we can look at in two parts:

A) The more suddenly the air pressure changes as you move in any horizontal direction, the stronger the wind. Here is a little mathematical note: if the strength of the pressure gradient (the line pointing from highest to lowest pressure) is directly proportional to the wind speed, we have a Geostrophic relation. That is, an ideal, frictionless situation.  Conditions are almost like that high up above the ground.

The strength of this relationship depends on how far North you are. Technically, this is because of the change in the Coriolis parameter, which is proportional to the trigonometric sine of the latitude.

B) The wind in this case will blow from your left if you look horizontally in the direction of the greatest pressure decrease. Towards the Low.

Meteorologists use a "Geostrophic Wind Scale", an analog forecasting ruler that helps them do this math quickly.

Current weather jet streams

When analyzing jet streams that are always in place somewhere high up in the atmosphere, we mark the middle of a core or "river" of high winds resulting from the Buys Ballot Law, with a "J".  This identifies the jet stream.

Weather Jet Streams

Some jets are low in altitude and can be seen by erratic motion on aviation wind socks and other wind instruments that display both wind speed and direction. By the way, the socks give people on the airfield a quick idea of what the wind conditions are like. They provide a convenient visual indication of surface wind speed, direction and turbulence, regardless of its causes.

The jet stream flows we usually talk about occur at an elevation of around 30,000 feet or more. The jet stream helps to define the speed and direction of nearby synoptic and mesoscale weather systems by pushing them along the jet's own flow direction.

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Search this site for more information now. For further details, read about upper air analysis Go back from Weather Jet Streams to the Forecast Map Weather web page or visit the Stuff in the Air homepage.

Search this site for more information now.

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