What is atmospheric circulation?

Solar radiation that reaches the Earth passes through the atmosphere and is either absorbed or reflected by the atmosphere and Earth’s surface. Most of this absorption happens on Earth’s surfaces, which increases the temperature of both land and water. A small amount of heat in the first few centimeters of the atmosphere is transferred from the surface by conduction, the process of molecules colliding and transferring energy. Because air molecules are farther apart than they are in liquids or solids, they do not collide as frequently as in liquids and solids, and air is a poor conductor of heat. Most heat is transferred in the atmosphere by radiation and convection.

Sunlight absorbed by Earth’s surfaces is re-radiated as heat, warming the atmosphere from the bottom up. This heat is absorbed and re-radiated by greenhouse gases in the atmosphere, resulting in the greenhouse effect. Warmed air expands and becomes less dense than cool air, so warmed air near the surface of the Earth rises up. Cooler air from above sinks, and air moves horizontally to replace the rising warm air, which we experience as wind over the surface of the Earth. This transfer of heat because of density differences in air is called convection. The major patterns in atmospheric circulation around the tropics (from around latitudes of 30^o N to 30^oS) are the result of convection that occurs because areas around the equator receive more sunlight than higher latitudes (see absorption and reflection of sunlight). These air masses, called the Hadley Cell,  rise near the equator and travel north and south, transporting heat and water towards the poles.

Patterns of air movement are further complicated because of Earth’s spin. Air moving from the equator towards the poles does not travel in a straight line, but is deflected because of the Coriolis effect (to learn more see links below), adding to the complexity of atmospheric circulation patterns. Additionally, the uneven distribution of continents and oceans and the presence of mountain ranges make the details of atmospheric circulation patterns far more complicated than the three cell model (shown above).

Variation in the amount of solar radiation absorbed, and the amount of heat re-radiating from Earth’s land and oceans results in temperature differences in air over different types of terrain. For example, sea breezes occur because land heats up and cools down faster than water, so that the land is warmer during the day and breezes flow from the sea inland, but the ocean is warmer than land at night, so the wind blows from land to sea.

Atmospheric circulation transports heat over the surface of the Earth that affects the water cycle, including the formation of clouds and precipitation events. The movement of air masses brings us our daily weather, and long-term patterns in circulation determine regional climate and ecosystems. Surface ocean currents patterns result from wind pushing on the surface of the water, and these currents also transport heat across the globe. Changes in the amount and distribution of heat in the Earth system due to an enhanced greenhouse effect from human activities is altering atmospheric and ocean circulation patterns that, in turn, alter environments around the globe.

Earth system models about atmospheric circulation

This model shows some of the cause and effect relationships among components of the Earth system related to atmospheric circulation. While this model does not depict the circulation patterns that results from uneven heating of the Earth’s surface (as shown above), it summarizes the key concepts involved in explaining this process. Hover over the icons for brief explanations; click on the icons to learn more about each topic. Download the Earth system models on this page.

This model shows some of the additional phenomena that alter atmospheric circulation patterns over millions of years, including the distribution of continents and oceans and mountain building. Changes in atmospheric circulation also transports heat that drives the water cycle, including cloud formation and precipitation patterns. In turn, the energy absorbed and released in the water cycle also contributes to atmospheric circulation. While this model does not depict the uneven heating of the Earth’s surface that results in atmospheric circulation, it summarizes the key concepts involved in explaining this global process.

How human activities influence atmospheric circulation

The Earth system model below includes some of the ways that human activities affect atmospheric circulation by adding greenhouse gases to the atmosphere and increasing Earth’s average temperature. Because the Arctic region is especially sensitive to overall warming compared to lower latitudes, the temperature gradient between the mid-latitudes and the pole is being reduced. This increases waviness in the north polar jet stream. As the atmosphere continues to warm, scientists expect to see much deeper north-south waves, which will cause changes in the jet stream. This could result in weather, both stormy and clear, persisting for much longer than would be considered normal over any particular area. Hover over or click on the icons to learn more about these human causes of change and how they influence atmospheric circulation.

Explore the Earth System

Click the icons and bolded terms (e.g. re-radiation of heat, airborne particles, etc.) on this page to learn more about these process and phenomena. Alternatively, explore the Understanding Global Change Infographic and find new topics that are of interest and/or locally relevant to you.

To learn more about teaching the absorption and reflection of sunlight, visit the Teaching Resources page.

Investigate

Learn more in these real-world examples, and challenge yourself to construct a model that explains the Earth system relationships.

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Links to Learn More

• National Weather Service: Global Circulations
• National Weather Service: The Jet Stream
• National Center for Atmospheric Research: Conduction
• National Center for Atmospheric Research: A Global Look at Moving Air: Atmospheric Circulation
• NOAA: Weather Systems and Patterns
• NOAA: What are sea breezes and why do they occur?