Where are the principal jetstreams in the atmosphere, and what are their characteristics?
The Polar Front Jet
As its name implies, this jet stream is associated with the marked discontinuity found at the boundary of well defined air masses - polar to the north/sub tropical to the south (in the northern hemisphere), conventionally found at the polar front. It meanders markedly in response to global/regional scale atmospheric changes but has a latitudinal 'home' roughly from 45 to 65 deg N/S. Its altitude is somewhere between 28000 ft to 34000 ft (8.5 - 10.5 km), with its own distinctive tropopause level. Speeds are of the order 80-130 knots (40-65 m/s), but may be as high as 180 knots (90 m/s), and downstream of main continental land masses in late winter/early spring, in excess of 200 knots (100 m/s). Although it is regarded as a 'single' ribbon of strength encircling the hemispheres, in reality the jet is broken and in developmental situations, can become very distorted with new jets re-forming at different levels from the 'main' baroclinic jet. (NB: during the winter half-year, jet-streams can be found at even higher latitudes in both hemispheres, roughly around 18000 ft (circa 5.5 km), which are named Arctic (or Antarctic) jets. These are again tied to a discontinuity between air masses (a frontal zone, or Arctic / Antarctic front), but this time between a very cold (and relatively shallow) 'arctic' airmass and somewhat less cold polar-maritime or polar-continental air. They are most evident (in the Northern Hemisphere), across Canada, the far north of the USA, northern Scandinavia, North Russia & other high-latitude regions. However, at times, they come further south, interacting with the PFJ, with sometimes dramatic developmental consequences.)
The Sub Tropical Jet
The average level of the core of this westerly jet lies at an altitude of about 40 000 ft/12 km, just below the tropical tropopause. It occurs in the latitude range 25-40 deg N/S, and is most marked during the winter and early spring of each hemisphere, but is not associated with any surface frontal structure. Its existence owes more to the fact that air in the high-level (poleward travelling) leg of the Hadley circulation conserves its angular momentum, being effectively 'turned' towards the east and finally concentrated in this ribbon of strong westerly wind. Because the Hadley circulation, and mid-latitude north/south linking flows are governed by seasonal heat differences north-to-south, then the STJ does vary, as noted above. Wind speeds are generally 80-150 knots (40-75 m/s), but can be much greater over eastern seaboards of large land masses, e.g. speeds of 400 kt (200 m/s) have been reported over east Asia/NW Pacific. From time-to-time, the STJ and the Polar Front Jet can interact with marked developmental consequences.
Stratospheric Night Jet
This occurs at times during the winter and early spring when the stratosphere near the poles is much colder than it is further south due to the absence of insolation at these times of the year. Its direction is westerly overall, with high variability, and has speeds in the range 100-200 kt (50-100 m/s) at altitudes around 70 000 ft/21 km and occurs on the poleward side of latitude 70 degrees.
Equatorial Easterly Jet
This jet occurs in the northern summer between 10 and 20 deg N, chiefly over or just to the south of high land masses such as in Asia and Africa. Its occurrence is due to a temperature gradient with colder air to the south which produces sufficient temperature differential above 50 000 ft/15 km to give wind speeds of over 100 kt (50 m/s). Because colder temperatures at height are to the south, it is an easterly jet. (This jet is now more usually known as the Tropical Easterly Jet(TEJ) ... perhaps more correctly as it lies some distance from the Equator.)