Polar Jet
Marked by a concentration of isotherms and strong vertical
shear, this jet is the boundary between the polar air and the
subtropical air. It often divides into two branches, the north and
the south, and marks the high speed core of the prevailing
westerlies. It is associated with the location and motion of the
high and low pressure areas of the middle latitudes, and therefore,
is variable in position, elevation, and wind speed. Its position
tends to migrate south in the Northern Hemispheric winter and north
in the summer, and its core winds increase during the winter and
become less strong in the summer.