<P> Polar jet streams are typically located near the 250 hPa (about 1 / 4 atmosphere) pressure level, or 7 to 12 kilometres (4.3 to 7.5 mi) above sea level, while the weaker subtropical jet streams are much higher, between 10 and 16 kilometres (6.2 and 9.9 mi). Jet streams wander laterally dramatically, and have large changes in their altitude . The jet streams form near breaks in the tropopause, at the transitions between the Polar, Ferrel and Hadley circulation cells, and whose circulation, with the Coriolis force acting on those masses, drives the jet streams . The Polar jets, at lower altitude, and often intruding into mid-latitudes, strongly affects weather and aviation . The polar jet stream is most commonly found between latitudes 30 ° and 60 ° (closer to 60 °), while the subtropical jet streams are located close to latitude 30 ° . The northern Polar jet stream is said to "follow the sun" as it slowly migrates northward as that hemisphere warms, and southward again as it cools . </P> <P> The width of a jet stream is typically a few hundred kilometres or miles and its vertical thickness often less than five kilometres (3.1 miles). </P> <P> Jet streams are typically continuous over long distances, but discontinuities are common . The path of the jet typically has a meandering shape, and these meanders themselves propagate eastward, at lower speeds than that of the actual wind within the flow . Each large meander, or wave, within the jet stream is known as a Rossby wave (planetary wave). Rossby waves are caused by changes in the Coriolis effect with latitude . Shortwave troughs, are smaller scale waves superimposed on the Rossby waves, with a scale of 1,000 to 4,000 kilometres (620--2,490 mi) long, that move along through the flow pattern around large scale, or longwave, "ridges" and "troughs" within Rossby waves . Jet streams can split into two when it encounters an upper - level low, that diverts a portion of the jet stream under its base, while the remainder of the jet moves by to its north . </P> <P> The wind speeds are greatest where temperature differences (gradient) between air masses are greatest, and often exceed 92 km / h (50 kn; 57 mph). Speeds over 398 km / h (215 kn; 247 mph) have been measured . </P>

Where are the jetstreams located in the atmosphere