Polar Anticyclone

GS1 – Geography

Context  

An intense cold wave hit South America due to the intrusion of a strong polar anticyclone, resulting in rare snowfall in Chile’s Atacama Desert—the first in over a decade. This was caused by an unusually northward extension of an Antarctic high-pressure system.

Understanding Polar Anticyclones:

A polar anticyclone refers to a high-pressure system that originates over polar areas due to the descent of cold air. These systems are strongest in winter when there is significant heat loss through radiation.

• Nature: Cold-core high-pressure systems, most intense near the ground, caused by sinking, dense cold air.
• Surface Effects: The descending cold air increases surface pressure, resulting in stable atmospheric conditions—clear skies, fog, frost, and sharp nighttime cooling.
• Seasonal Movement:
  • Winter: They shift eastward and towards the equator, often bringing cold spells to lower latitudes.
  • Summer: Although weaker, they may still move equatorward, contributing to cool and dry conditions.
• Weather Impact: They interact with polar fronts and can lead to cold fronts, triggering storms and sudden temperature drops.

Prominent Examples:

• Siberian High – Eurasia
• Canadian High – North America
• Antarctic High – South Pole

Formation Mechanism:

1. Surface Cooling: Ground-level cooling increases air density, causing it to sink.
2. Pressure Rise: The descending air compresses and slightly warms, though remains denser, enhancing surface pressure.
3. Rotation: The accumulating air mass diverges due to the Coriolis effect, leading to a rotating high-pressure system.

Relevance to India:

• While India is geographically beyond the direct reach of polar anticyclones, it experiences indirect influence through the Central Asian Highs during winter.

Impacts on India:

• Cold Waves: Outflows from the Siberian High induce cold wave conditions in northern India.
• Fog: Stable, cold air encourages overnight cooling, promoting dense fog in the Indo-Gangetic plain.
• Western Disturbances: These highs steer western disturbances toward Northwest India and the western Himalayas.