polar-front jet stream The jet stream that is observed in different positions over middle and higher latitudes at heights of 10–13 km, and is associated with the boundary zone between polar and tropical air above the polar front. Maximum velocity averages 60 m/s, but can be twice this in extreme cases. The jet is typically discontinuous but at times can extend almost around the globe. It is more persistent in winter in response to the stronger temperature gradient between north and south than in summer. The jet is related to the development of surface frontal depressions of middle latitudes.

polar-front jet stream The jet stream observed in different positions over middle and higher latitudes at heights of 10–13 km, and associated with the boundary zone between polar and tropical air above the polar front. Maximum velocity averages 60 m/s, but can be twice this in extreme cases. The jet is typically discontinuous but at times can extend almost around the globe. It is more persistent in winter in response to the stronger temperature gradient between north and south than in summer. The jet is related to the development of surface frontal depressions of middle latitudes.