What is global circulation? | Part Two | The three cells

Met Office - Learn About Weather

20 Feb 201803:35

Summary

TLDRThis video script explains how Earth's uneven heating leads to global circulation patterns. With no rotation, a simple landmass would have one cell per hemisphere. However, Earth's rotation, land-sea distribution, and topography create a 3-cell pattern: Hadley (equatorial), Ferrel (mid-latitude), and Polar cells. These cells redistribute heat, creating climatic zones with varying weather patterns, such as rainforests near the equator and deserts in high-pressure areas. The script also hints at upcoming content on jet streams and prevailing winds.

Takeaways

🌍 The Earth's different regions heat up unevenly, with the equator receiving more heat than the poles.
🔄 Global circulation aims to redistribute this heat unevenly across the Earth.
🌬️ Without Earth's rotation and with no oceans, there would be a single circulatory cell in each hemisphere.
🌡️ The Hadley cells are the largest cells at the equator, where warm air rises and spreads out under the tropopause.
🌀 The Ferrel cells are mid-latitude cells that flow in the opposite direction to the Hadley and polar cells.
❄️ The polar cells are the smallest, with cold air descending in polar regions and flowing towards the mid-latitudes.
🌤️ The tropopause acts as a lid to the lowest part of the atmosphere, containing all of our weather.
🌧️ Rising air creates low-pressure areas, which are often associated with rainforests and wet climates.
🏜️ Descending air leads to high-pressure areas, resulting in clear skies and little rainfall, often found in desert regions.
❄️ Antarctica, despite being cold, is considered a desert due to its location under the descending branch of the Polar cell.
🌀 The Earth's rotation contributes to the formation of jet streams and prevailing winds.

Q & A

How does the Earth's rotation affect global circulation?
-The Earth's rotation complicates the circulation system, leading to a 3-cell pattern in both the northern and southern hemispheres instead of a single cell.
What is the role of global circulation in redistributing heat?
-Global circulation redistributes heat from the equator, which receives more heat from the Sun, to the poles.
What would happen if the Earth did not rotate and was a simple landmass with no oceans?
-There would be a single circulatory cell in each hemisphere, with hot air rising at the equator and flowing toward the poles, then sinking and returning towards the equator.
What are the three types of cells in the Earth's circulation system?
-The three types of cells are the Hadley cells, the polar cells, and the Ferrel cells.
How high do the warm air in the Hadley cells rise?
-The warm air in the Hadley cells rises to a height of about 18 kilometers.
What is the tropopause and how does it relate to the Hadley cells?
-The tropopause acts as a lid to the lowest part of the atmosphere, which contains all of our weather. The warm air from the Hadley cells spreads out underneath the tropopause.
What is unique about the Ferrel cells compared to the other cells?
-The Ferrel cells are not driven by temperature and flow in the opposite direction to the Hadley and polar cells.
How do the rising and descending parts of the circulation cells create climatic zones?
-Rising air creates areas of low pressure, leading to more rainfall, while descending air creates areas of high pressure, resulting in clear skies and little rainfall.
Why are the largest areas of rainforests found near the equator?
-The largest areas of rainforests are found near the equator because of the low pressure created by rising air in the Hadley cells.
Why does the United Kingdom have a relatively wet climate?
-The United Kingdom has a relatively wet climate due to the low pressure areas created by the rising air in the circulation cells.
Why are some deserts not hot, like Antarctica?
-Antarctica is a desert under the descending branch of the Polar cell, and it is cold because it is at a high latitude where temperatures are generally lower.
What is the significance of the jet streams and prevailing winds in relation to the Earth's rotation?
-The rotation of the Earth gives us jet streams and prevailing winds, which are not directly mentioned in the script but are related to the Earth's circulation patterns and can affect weather systems.

Outlines

00:00

🌍 Global Heat Distribution and Atmospheric Circulation

This paragraph discusses how the Earth's varying heat absorption due to its rotation and land-sea distribution leads to a complex global circulation system. Without rotation, a simple landmass would have a single cell circulation pattern, but the Earth's rotation and unequal land-ocean distribution create a 3-cell pattern in each hemisphere. The Hadley cells at the equator cause warm air to rise and spread out under the tropopause before descending and returning to the equator. Polar cells involve cold air descending in polar regions and rising as it warms up. Ferrel cells, unlike the others, are not temperature-driven and flow in the opposite direction, acting as a gear in the system. These cells result in semi-permanent high and low-pressure areas, influencing climatic zones and weather patterns.

Mindmap

Keywords

💡Equator

The equator is the imaginary line that divides the Earth into the northern and southern hemispheres. In the video, the equator is significant because it receives the most heat from the Sun, driving global circulation. The warmer air at the equator rises and flows towards the poles, creating a fundamental part of the Earth's climate system.

💡Poles

The poles refer to the northernmost and southernmost points on Earth, which receive less sunlight compared to the equator. In the video, they are important because the cooler, denser air from the poles descends and flows toward lower latitudes, creating the polar cells in the Earth's circulation system.

💡Hadley Cells

Hadley cells are large atmospheric circulation cells located near the equator. In the video, they are described as the largest circulation cells, where warm air rises at the equator and spreads out towards the poles before cooling and sinking. They play a key role in distributing heat from the equator towards the poles.

💡Polar Cells

Polar cells are the smallest atmospheric circulation cells located near the poles. In the video, they are described as consisting of cold, dense air that descends in the polar regions and flows towards lower latitudes, eventually warming and rising back toward the poles. This cell system helps balance the Earth's temperature by transporting colder air.

💡Ferrel Cells

Ferrel cells are atmospheric circulation cells found between the Hadley and polar cells. Unlike the Hadley and polar cells, they are not directly driven by temperature differences but instead act like a gear between the other two cells. In the video, they are important for explaining the mid-latitude weather systems, including those that affect regions like the UK.

💡Global Circulation

Global circulation refers to the large-scale movement of air that helps distribute heat across the planet. The video explains that without Earth's rotation or oceans, there would only be one circulation cell in each hemisphere. However, due to rotation and other factors, the Earth's circulation is more complex, leading to a three-cell pattern in each hemisphere.

💡Tropopause

The tropopause is the boundary between the lowest layer of Earth's atmosphere (the troposphere) and the stratosphere. In the video, it is described as a 'lid' that limits the upward movement of air within weather systems. The Hadley cell's warm air rises to this boundary before spreading out, which is crucial to how weather patterns form.

💡High Pressure

High pressure refers to areas where the atmospheric pressure is greater than surrounding areas. In the video, it explains that these regions, created by descending air in the circulation cells, lead to clearer skies and dry conditions. For example, deserts are often found under high-pressure zones, where little rainfall occurs.

💡Low Pressure

Low pressure refers to areas where the atmospheric pressure is lower than surrounding areas. The video mentions that low-pressure regions are created by rising air within circulation cells, which often results in more rainfall. This is why rainforests, such as those near the equator, are located in low-pressure areas.

💡Jet Streams

Jet streams are fast-moving, narrow air currents in the atmosphere that are influenced by Earth's rotation and atmospheric circulation. While the video hints at a future explanation of jet streams, they are linked to global circulation patterns and play a significant role in determining weather and wind patterns across the planet.

Highlights

Different parts of the Earth heat up differently, with the equator receiving more heat from the Sun than the poles.

The purpose of global circulation is to redistribute this heat.

Without Earth's rotation and with no oceans, there would be a single circulatory cell in each hemisphere.

Hotter air would rise at the equator and flow toward the poles in a simple landmass scenario.

Air would sink as it cools and then return towards the equator.

The unequal distribution of land and ocean and the speed of Earth's rotation complicate the circulation system.

This results in a 3-cell pattern in both the northern and southern hemispheres.

The largest cells are the Hadley cells at the equator, where warm air rises to about 18 kilometers.

The tropopause acts as a lid to the lowest part of the atmosphere containing all weather.

Warm air spreads towards the poles, cooling and sinking before descending back to the surface.

The smallest cells are the polar cells, where cold dense air descends in polar regions.

Ferrel cells exist between the Hadley and polar cells and are not driven by temperature.

Ferrel cells flow in the opposite direction to the Hadley and polar cells, acting like a gear.

Circulating cells transport heat from the equator to the poles and create semi-permanent high and low-pressure areas.

Areas of low pressure where air is rising tend to have more rainfall, such as rainforests near the equator.

Areas of high pressure where air is descending have clear skies and little rainfall, leading to desert regions.

Not all deserts are hot; Antarctica is a cold desert under the descending branch of the Polar cell.

Antarctica is the largest and driest desert, despite more precipitation falling in the Sahara.

The rotation of the Earth gives us jet streams and prevailing winds, which will be explained in the next video.