The three cells, Hadley, Ferrel, and Polar, (sometimes collectively called the Hadley Cells) have zones of interaction near the 30° and 60° parallels. These are places where warm and cold air meet. In the higher levels of the atmosphere about 12 kilometres high, in the grooves between the Hadley cells, strong narrow currents of wind flow from west to east. These are the jet streams.They average 50 knots and sometimes reach more than 200 knots. The one at 30° is called the 'subtropical jetstream' and the one at 60° the 'polar jetstream'.
Imagine the Earth sitting cocooned inside a stack of six doughnuts of different sizes. Small ones at the poles, middlesized ones between 60° and 30°, and larger ones near the equator. These are the Hadley cells. Between each doughnut lies a strand of fettucine. These are the jetstreams.