WESTERLIES

WESTERLIES

Westerlies are winds that blow from the subtropical high-pressure belts towards the sub-polar low-pressure belts. They blow southwest to northeast in the Northern Hemisphere and northwest to southeast in the Southern Hemisphere.

• Westerlies in the Southern Hemisphere: These winds are strong and persistent because of the vast expanse of water.
• Westerlies in the Northern Hemisphere: They tend to be more irregular due to the uneven landmasses.
• Development: Westerlies are best developed between 40° and 65°S latitudes. This zone is often referred to as the Roaring Forties, Furious Fifties, and Shrieking Sixties, which are significant for sailors.
• Characteristics: These winds can produce wet spells and seasonal variations.

Features of the Westerlies:

• Location: Westerlies blow in the middle latitudes between 30° and 60° latitude. They are also called antitrade winds because their direction is opposite to that of trade winds.
• Anomalies: In the Southern Hemisphere, westerlies are stronger due to the greater ocean area compared to the land area, unlike the Northern Hemisphere where more land exists.
• Ocean Currents: The currents in the Northern Hemisphere are weaker than those in the Southern Hemisphere, partly due to the strength differences in the westerlies of each hemisphere.
• Directions: Westerlies originate from high-pressure areas in the horse latitudes, and flow toward the poles. Under the Coriolis force, they become the south westerlies in the Northern Hemisphere and north westerlies in the Southern Hemisphere.
• Seasonal Variation:
  • Westerlies are strongest in winter when the pressure is low over the poles.
  • They are weakest in summer, especially in the Southern Hemisphere.
• Cyclones: Westerlies are associated with extra tropical cyclones in the middle latitudes, helping to steer these systems from west to east.
• Storms: When cold polar winds converge with warm westerlies, stormy weather results. The speed of the westerlies increases towards the poles, creating Roaring Forties (40°-50°S), Furious Fifties (50°S), and Shrieking Sixties (60°S).

Effects of Westerlies:

• Ocean Currents in the Southern Hemisphere: Westerlies drive powerful ocean currents like the Antarctic Circumpolar Current (ACC), which transports nutrient-rich water around Antarctica.
• Transporting Nutrients: ACC is the largest ocean current, moving vast amounts of cold, nutrient-rich water that supports marine ecosystems.
• Helps Navigation:
  • Westerlies in the Roaring Forties were vital for explorers and traders, helping ships from Europe and Asia reach spice markets in Southeast Asia and Australia.
  • Example: The tip of South America and Australia, the islands of New Zealand, and other landmasses played key roles in navigation.
• Drivers of Regional Oceanography: Leakages in ocean currents intensify during strong westerlies, impacting regional oceanography over southern Africa.
  • Example: The Agulhas Current and Benguela upwelling are driven by intensified westerlies.

Issues Associated with Westerlies:

• Poleward Migration Due to Climate Change: Westerlies are gradually moving poleward due to global warming, altering wind patterns in the middle latitudes.
• Precipitation Patterns: Changes in westerlies impact storm systems and precipitation. Studies show a significant shift in these patterns due to climate change.
• Droughts and Wildfires: Changes in the Southern Hemisphere Westerly winds (SHW) have been linked to continental droughts and wildfires.
• Sea-Level Rise: Warming has led to melting ice shelves in Antarctica, contributing to sea-level rise.

Importance of Planetary Winds:

1. Temperature Distribution: Planetary winds maintain a balance in temperature globally, ensuring cool winds reach hotter areas and mitigating extreme temperature variations.
2. Ocean Currents: These winds drive ocean currents, affecting water movement, salinity changes, and the transfer of nutrients, all of which are essential for marine life and navigation.
3. Rainfall: Planetary winds move clouds, helping distribute moisture globally and bringing rainfall. This is especially significant for regions like India, where trade winds bring the monsoon.
   • Example: Trade winds contribute to the monsoon system in India.
4. Fishing: These winds bring nutrient-rich water to coastal areas, which enhances marine life, including fish populations.
5. Sailing: Prevailing winds are beneficial for navigation and sailing, allowing vessels to travel faster and save fuel.
6. Vegetation: Planetary winds promote healthy vegetation growth by helping to distribute moisture and regulate temperature.