How does the polar-front jet stream affect the movement of air masses?
The polar-front jet stream is a frontal wind, located just below the tropopause, blowing parallel to the surface fronts, moving with them, and draining the air rising from the fronts. It is strongest between latitudes 40 and 60 °N. This jet stream causes strong horizontal shifts in temperature and pressure since it marks the boundary between cold polar air and warm tropical air, where the steepness of the isotherms is at a maximum. It has important effects on convergence and divergence in the upper air. For example, at the ‘jet entrance’, the pressure gradient steepens, and the wind becomes jet-fast, leading to high-level convergence. A strong polar-front jet is associated with rapidly moving depressions; a weak jet with a blocking pattern where northerly and southerly air streams dominate. The polar-front jet stream moves from west to east and meanders across the U.S. and Canada. A southerly dip can mean cold temperatures for the southern states. A northerly bend can bring warmer than
