Anticyclone

An anticyclone is a large-scale atmospheric system characterized by high surface pressure and descending air, or subsidence, which tends to suppress cloud formation and produce clear or dry weather. In the Northern Hemisphere, winds around an anticyclone rotate clockwise and diverge outward from the center; in the Southern Hemisphere, they rotate counterclockwise with outward flow. The overall effect is a stable air column with relatively calm conditions, though strong pressure gradients can still generate gusty winds.

Anticyclones form when the atmosphere develops a region of comparatively high pressure, often from subsidence in the upper troposphere (a ridge) or radiational cooling at night. They can be persistent, especially when they become blocking highs that steer other weather systems for days or weeks. Subtropical highs, such as the Azores High or Pacific High, are common large-scale examples; continental interiors can host the Siberian High in winter.

Weather associated with anticyclones is typically fair and dry, with clear skies due to the sinking air discouraging cloud formation. However, stagnation under a strong anticyclone can lead to temperature extremes, with daytime heating under sunny skies and radiational cooling at night producing frost or fog. In summer, the same processes can contribute to heatwaves and drought in some regions.

Anticyclones contrast with cyclones, which are low-pressure systems featuring rising air, cloud development, and precipitation. The wind flow around highs and lows reverses with hemisphere due to the Coriolis effect, and anticyclones can play a key role in blocking patterns and shaping regional weather for extended periods.