Walker circulation

Wind blows across the big ocean.

It moves warm air to the west. This makes warm and wet weather. Large storms can form there.

The wind also moves the water. It pushes warm water to one side. This makes the ocean higher there.

On the other side, the wind helps. It brings cold water up from deep down. This cold water helps more fish grow.

Sometimes this wind cycle changes. It can get weaker or stronger. These changes change the weather for many lands. It is a big cycle of air and water.

The Walker circulation is a way air moves in the tropics.

It is a big loop of air and water. This loop starts with wind. Easterly trade winds blow from east to west. These winds move warm air toward the west. This makes the western Pacific warm and wet. Large storms and typhoons form there. The ocean is also about 60 cm higher in the west.

On the other side, the wind helps the ocean. It pulls cold water up from deep down. This is called upwelling. This cold water helps more fish grow.

The cold water stays near the surface in the east. This creates a cold tongue of water.

Sometimes this cycle changes. During El Niño, the winds get weak. The ocean surface warms up. During La Niña, the winds get strong. This makes the ocean even colder.

These changes affect weather all over the world. A scientist named Gilbert Walker discovered these patterns long ago.

The Walker circulation is a huge loop of air and water in the tropics.

This movement happens in the lower atmosphere, which is called the troposphere. It acts like a giant engine that moves heat around the Earth. The air follows a closed path that goes both sideways and up and down. This happens because of heat differences between the ocean and the land. It is a very important part of how our world stays balanced. This circulation helps decide where weather happens in the tropical regions.

This system works through a specific step-by-step process. First, easterly trade winds blow across the ocean from east to west. These winds push warm air and sun-warmed water toward the west. This makes the western Pacific warm, wet, and full of low pressure. Huge thunderstorms and typhoons often form in these wet areas.

Meanwhile, the winds help the eastern Pacific stay cool. They pull cold water up from deep below the surface. This process is called upwelling, and it brings nutrients up for fish. This creates a long area of cool water called a cold tongue.

We know about this because of a scientist named Gilbert Walker. He was a mathematician who worked in India starting in 1904. He studied the Indian Ocean monsoon to understand why rains failed. Walker looked at vast amounts of weather data from around the world. He discovered a "seesaw" of air pressure between the Indian and Pacific Oceans. He showed how temperature, wind, and rain were all linked together. He even proved that sunspots were not the cause of these changes.

Scientists use specific names to describe how this loop changes over time. A meteorologist named Jacob Bjerknes first used the term "Walker Circulation" in 1969. He was describing the way the ocean and air work together. When the circulation is weak, it is called an El Niño event. During El Niño, the ocean surface becomes warmer than usual.

When the circulation is very strong, it is called La Niña. This makes the eastern ocean even colder than normal. These cycles change the depth of the thermocline, which is the layer where water temperature changes quickly.

Understanding this loop helps us see how the ocean and air talk to each other. It is like a feedback loop where one change causes another. For example, strong winds make the east ocean colder. This cold water makes the winds blow even harder. This link between the wind and the sea is what keeps the cycle moving.

Even the position of the sun in the summer can change how this works. By watching these patterns, we can better understand the weather of our whole planet.

The Walker circulation is a conceptual model describing the atmospheric airflow in the tropics. This circulation occurs within the troposphere, which is the lowest layer of the atmosphere. It involves a closed loop of air moving in both zonal and vertical directions. The circulation is driven by differences in heat distribution between the ocean and the land.

This system is vital because it helps regulate tropical weather patterns and ocean temperatures. It creates a complex relationship between the air above and the water below.

To understand how it works, we must look at the specific movement of air and water. The process begins with the pressure gradient force. This force results from a high-pressure system over the eastern Pacific Ocean and a low-pressure system over Indonesia. Because of this difference, easterly trade winds blow across the surface from east to west. These winds push sun-warmed air and surface water toward the western Pacific.

As this warm water collects in the west, the ocean level there rises by about 60 cm. This warm, wet environment in the west creates low-pressure weather, leading to thunderstorms and typhoons.

As the warm air rises in the west, it must eventually return to the east. This creates a cycle where the air and water are returned to the eastern part of the basin. In the east, the air is much drier and the water is much cooler. This cooling happens because of a process called upwelling. The easterly winds pull cold, deep sea water up to the surface. This creates a long area of cool water known as the equatorial cold tongue.

This upwelling also brings nutrient-rich water to the surface, which helps increase fishing stocks.

The strength of this circulation can change, leading to different climatic phases. During a normal period, the circulation maintains a steady balance. However, an El Niño episode occurs when this cycle breaks down. In an El Niño event, the circulation weakens or stops entirely. This causes the ocean surface in the eastern Pacific to become warmer than average. Conversely, a La Niña event happens when the Walker circulation becomes markedly stronger. This intensifies the upwelling of cold water, making the eastern sea surface temperatures much colder than usual.

These changes in the atmosphere and ocean are deeply connected through feedback loops. One such mechanism is known as coupled ocean-atmosphere feedback. For example, strong easterly winds cause the sea surface temperature to fall in the east. This temperature drop enhances the zonal heat contrast between the east and west. This increased contrast then intensifies the easterly winds even further. These stronger winds induce more equatorial upwelling and raise the thermocline in the east. The thermocline is the layer in the ocean where temperature changes rapidly with depth.

Our knowledge of these patterns comes from the work of Gilbert Walker. He was an applied mathematician and the director-general of observatories in India starting in 1904. While studying the Indian Ocean monsoon, he discovered the Southern Oscillation. This is a "seesaw" of atmospheric pressure between the Indian and Pacific Oceans. Walker analyzed vast amounts of data to show how pressure, rainfall, and temperature were linked. He even argued against the idea that sunspots caused these temperature variations. The term "Walker Circulation" was later applied to his model by meteorologist Jacob Bjerknes in 1969.

The Walker circulation affects different parts of the world in various ways. While we often discuss the Pacific, there are also Walker circulations in the tropical Indian and Atlantic basins. In the northern summer, the Indian basin experiences westerly surface winds. However, the Pacific and Atlantic basins experience easterly winds. These differences cause the temperature structures of the three oceans to show dramatic asymmetries. For instance, the equatorial Pacific and Atlantic both have cool surface temperatures in the east during the northern summer. In contrast, cooler surface temperatures in the western Indian Ocean prevail during this time.