The coldest month is usually quite mild, although frosts are not uncommon, and winter precipitation is derived primarily from frontal cyclones along the polar front.
22.
When the polar vortex is weak, high pressure zones of the mid latitudes may push poleward, moving the polar vortex, jet stream, and polar front equatorward.
23.
These extratropical convergence zones are occupied by the polar fronts where air masses of polar origin meet and clash with those of tropical or subtropical origin.
24.
The interface between the cold dry air mass of the pole and the warm moist air mass further south defines the location of the polar front.
25.
Again this was a role to co-ordinate a number of scattered units, this time across Norway, facing both the Russian Polar Front, the North Sea and Arctic Ocean.
26.
These lows produce a shorter fetch than polar fronts, however they can still generate heavy swells, since their slower movement increases the duration of a particular wind direction.
27.
The Pacific fronts, while lacking sharp temperature contrasts common with polar fronts, tend to draw large quantities of very mild, moist air, vital to thunderstorms, northward from the Gulf of Mexico.
28.
Much of the biology in the area occurs along the major fronts of the current, the Subtropical, Subantarctic, and the Antarctic Polar fronts, these are areas associated with well defined temperature changes.
29.
** Antarctic Circumpolar Current ( clockwise around Antarctica, from the Antarctic Divergence to the Subtropical Convergence; spans the Subantarctic Front and Antarctic Convergence ( = Antarctic polar front ), as in graph ).
30.
He joined the Massachusetts Institute of Technology ( MIT ) faculty in 1929, where he headed the development and adoption of the polar front theory of five-day weather prediction by the Weather Bureau.
