 The Northern Hemisphere and the Southern Hemisphere each have a polar jet and a subtropical jet.The northern hemisphere polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica all year round.The southern hemisphere mid-latitude jet is a relatively narrow band of strong winds stretching from the Earth's surface to the top of the troposphere at about 12 km increasing steadily in strength with height.