The discontinuous, variable front which forms over the North Atlantic and North Pacific, where polar maritime air meets tropical maritime air. The formation of mid-latitude depressions at the polar front is connected with the development of troughs in the polar front jet stream, a band of high-velocity winds in the wider Rossby waves. The polar front jet stream moves southwards in winter and northwards in summer. During an El Ninõ event, it shifts south, bringing cooler air, which might suppress tornado activity in the US Midwest. Mid-latitude aridity can result from the effect of mountains on the polar jet stream; see W. G. Whitford (2002). See Dupont et al. (2005) Geol. 33, 6 on the sensitivity of the Namibian upwelling to latitudinal shifts in the Southern Ocean polar front zone; Ingvaldsen (2005) Geophys. Res. Letter 32, LI6603 on the link between the polar front and the North Cape Current; and Hayes and Zenk (1977) NOAA Technical Report ERL PML 28 on the Antarctic Polar Front.

Polar easterlies blow east–west, from polar highs to sub-polar lows. A polar high is a mass of cold, heavy air, centred at the poles, and produced by downward, vertical air currents from the polar vortex, bringing high pressure at high latitudes. For polar low, see cold low.