Anti-cyclones, also known as high-pressure systems, are atmospheric circulations characterized by descending air at the center, which diverges outward in a clockwise direction in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Unlike cyclones (low-pressure systems), anti-cyclones typically bring stable weather conditions with clear skies and light winds.
1. Anti-Cyclones Associated with Tropical Cyclones
In the context of tropical cyclones, anti-cyclones can influence their behavior and intensity:
a. Subsidence:
- Subsidence Inversion: In the vicinity of a tropical cyclone, especially in its outer periphery, anti-cyclonic subsidence (descending air) can create a subsidence inversion. This inversion acts as a cap on convection, limiting the vertical development of thunderstorms and potentially weakening the cyclone.
b. Steering Influence:
- Steering Mechanism: Anti-cyclones located to the north of a tropical cyclone can act as a steering mechanism, guiding its path. The interaction between the cyclonic and anti-cyclonic circulations can influence the trajectory and speed of the cyclone.
Example:
- Subtropical Highs: In the North Atlantic basin, subtropical high-pressure systems (anti-cyclones) play a crucial role in steering hurricanes. These highs often guide hurricanes on a westward track towards the Caribbean Islands and the southeastern United States during the hurricane season.
2. Anti-Cyclones Associated with Temperate Cyclones (Extratropical Cyclones)
Temperate cyclones, or extratropical cyclones, often encounter anti-cyclones in their vicinity:
a. Blocking Patterns:
- Blocking Highs: Anti-cyclones can sometimes become stationary or slow-moving, creating blocking patterns. These blocking highs can persist for days or weeks, influencing the movement and track of extratropical cyclones.
b. Clear Skies and Stability:
- Clear Weather: In regions under the influence of an anti-cyclone, clear skies and stable weather conditions prevail due to the sinking motion of air, which suppresses cloud formation and precipitation.
Example:
- Scandinavian High: During winter, the Scandinavian high-pressure system often becomes established over northern Europe. This anti-cyclone can block the eastward movement of extratropical cyclones, leading to prolonged cold spells and dry weather conditions over parts of Europe.
Anti-Cyclones in India
Impact on Weather:
- North India: During winter, anti-cyclones over northern India can bring dry and cold weather conditions, contributing to fog formation and poor visibility in the Indo-Gangetic plains.
- Monsoon Season: In the monsoon season, anti-cyclones in the Arabian Sea and Bay of Bengal can weaken the monsoon circulation, leading to breaks or pauses in rainfall over parts of India.
Conclusion
Anti-cyclones are significant components of atmospheric circulation that influence the behavior of both tropical and temperate cyclones. While they generally bring stable weather conditions, their interaction with cyclonic systems can affect the intensity, movement, and impacts of cyclones worldwide. Understanding these interactions is essential for meteorologists to forecast weather patterns accurately and for communities to prepare for and mitigate the impacts of extreme weather events associated with both cyclonic and anti-cyclonic systems.
