subtropical jet stream The jet stream of subtropical latitudes. The change from a westerly direction in winter to an easterly one in summer influences the surface wind changes that mark the summer monsoon. The jet is related to a marked temperature gradient in the upper troposphere. The westerly jet moves towards the equator in winter and is associated with subsiding air and settled surface weather. In summer the jet moves towards the pole. At the seasonal extremes it tends at times to merge with the polar-front jet.

subtropical jet stream Jet stream of subtropical latitudes. The change from a westerly direction in winter to an easterly one in summer influences the surface wind changes that mark the summer monsoon. The jet is related to a marked temperature gradient in the upper troposphere. The westerly jet moves equatorward in winter and is associated with subsiding air and settled surface weather. In summer the jet moves poleward. At the seasonal extremes it tends at times to merge with the polarfront jet.