The Jet Stream
Jet streams can be observed as a more or less continuous narrow and meandering band of strong winds at levels around 300 hPa in the northern and southern hemisphere.
Figure 1: Schematic of the Polar and Subtropical Jets. © Lyndon State College Meteorology
Jet streams are usually found between the global circulation cells and result from strong horizontal temperature gradients and the Coriolis force acting on winds.
Figure 2: Position of the global jet streams in relation to atmospheric circulation cells. © NOAA
A zonal jet stream is characterized by a flow nearly parallel to lines of latitude; in a meridional pattern, the jet stream shows highly amplified troughs and ridges.
In a zonal flow, low pressure systems move quickly from west to east in the Northern hemisphere, while in a blocking situation, jet streams are highly meridional.
Figure 3: Meridional and zonal flow of the jet stream and the effect on jet streaks
Jet streaks do not easily pass around the corner of a trough because the ageostrophic wind acts against them. This is increasingly so, the stronger the jet and the stronger the curvature of the trough is.
Note:
Those parts of the jet stream with the highest wind speeds are called jet streaks; they are important to the process of cyclogenesis.