Polar front
Topic: Air Masses, Fronts, Cyclones and Thunderstorms · NCERT: Class 11, Ch 9 "Atmospheric Circulation and Weather Systems"
Meaning
The polar front is a semi-permanent front in the middle latitudes, near the subpolar lows at about 60°. "Semi-permanent" means it is present most of the time, though it shifts and bends. Along it, cold polar air meets warm subtropical air. Small waves form on this boundary. Some deepen into low-pressure systems, so most extratropical (temperate) cyclones are born along the polar front.
Example
Over the North Atlantic, the polar front lies between cold air from the Arctic and warm air from the subtropics. The depressions that bring rain and wind to north-west Europe, such as Britain and Norway, grow as waves along it.
Don't confuse with
- ITCZ (Inter-Tropical Convergence Zone): the ITCZ is near the equator, where the trade winds meet. It is not a boundary between cold and warm air masses, and temperate cyclones do not form along it.