Polar high
Topic: Atmospheric Pressure, Winds and General Circulation · NCERT: Class 11, Ch 9 "Atmospheric Circulation and Weather Systems"
Meaning
The polar high is a belt of high pressure over the North and South Poles. It is thermal in origin, which means temperature causes it. The ice-covered poles are very cold, so the air above them becomes dense and heavy and sinks. This sinking air builds up high pressure at the surface. From the polar high, cold, dry polar easterlies blow towards the subpolar lows near 60° N and S. In the three-cell model, this sinking air forms the downward part of the polar cell.
Example
Over the Antarctic ice sheet around the South Pole, very cold air sinks all the time. This keeps pressure high, and cold winds spread outwards from the ice.
Don't confuse with
- Polar vortex: this is a large area of low pressure and cold air circling each pole high up, in the stratosphere and upper troposphere. The polar high is a surface feature.
- Subtropical high: this is also a high, but it is dynamic. Air piles up and sinks near 30°. Cold does not cause it.