Global atmospheric circulation

This creates pressure differences, which, in turn, cause air to move in large-scale circulation patterns. Understanding these patterns and their components, such as the circulation cells, jet streams, and the Coriolis effect, is key to comprehending how Earth’s weather systems function.

The major circulation cells

The atmosphere is divided into three primary circulation cells in each hemisphere: Hadley cells, Ferrel cells, and Polar cells. These cells work together to transfer heat from the equator to the poles and influence weather patterns globally.

• Hadley cells: Located from the equator to about 30° latitude, warm air rises at the equator, specifically within the Intertropical Convergence Zone, cools, and sinks around 30° latitude, forming high-pressure areas. This movement creates the trade winds and is responsible for the tropical climates and desert regions. The high pressure areas at roughly 30 degrees latitude, cause air to flow outward, both toward the equator, and toward higher latitudes.
• Ferrel cells: Between 30° and 60° latitude, air from the subtropical high-pressure areas moves towards the poles, where it meets cold air from the polar regions. This convergence creates low-pressure systems and the westerlies, which influence weather in the mid-latitudes.
• Polar cells: At the poles, cold air sinks and moves toward the equator at the surface, where it meets warmer air from the Ferrel cells. This creates the polar easterlies, contributing to the cold climates near the poles.

The role of jet streams and the Coriolis effect

Both jet streams and the Coriolis effect are critical components that influence and shape global atmospheric circulation. Their effects are directly tied to how air moves across the planet, impacting weather patterns and climate.

• Jet streams: These fast-moving air currents, typically found at the boundaries of the circulation cells, help steer weather systems across regions, influencing the movement of low-pressure areas and storms. The polar jet stream, in particular, plays a key role in directing weather patterns and impacting mid-latitude climates.
• Coriolis effect: Caused by Earth's rotation, the Coriolis effect deflects moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection is crucial in shaping wind patterns within the circulation cells (e.g., trade winds, westerlies, polar easterlies) and helps maintain the organized movement of air in global circulation.

Both of these features are integral in shaping how air circulates across the planet, affecting everything from day-to-day weather to larger climate systems.

El Niño and La Niña: Disruptions to atmospheric circulation

El Niño and La Niña are phases of the El Niño-Southern Oscillation (ENSO), a natural climate phenomenon that disrupts the typical patterns of global atmospheric circulation, particularly in the Pacific Ocean. These disruptions have widespread impacts on weather systems around the world.

• El Niño: This phase occurs when trade winds weaken, causing warmer-than-usual sea surface temperatures in the central and eastern Pacific. The altered atmospheric circulation leads to shifts in rainfall, such as wetter conditions along the U.S. West Coast and drier regions in Southeast Asia and Australia.
  
  
• La Niña: In contrast, La Niña is characterized by stronger trade winds and cooler-than-usual sea surface temperatures in the Pacific, reinforcing typical weather patterns. This phase is often associated with wetter conditions in Southeast Asia and Australia, and drier weather in the U.S. Southwest.

Both El Niño and La Niña illustrate how changes in the ocean and atmospheric conditions can significantly alter global weather patterns and temporarily shift the typical flow of the atmosphere.

The importance of global atmospheric circulation

Understanding global atmospheric circulation is essential for predicting weather and managing the impacts of climate events on ecosystems, agriculture, and infrastructure. 

The interplay of circulation cells, jet streams, and the Coriolis effect regulates Earth's climate, while disruptions like El Niño and La Niña demonstrate how sensitive the system is to shifts in ocean and atmospheric conditions. This highlights the interconnectedness of Earth's climate and the importance of monitoring these patterns for long-term weather forecasting.