Atmospheric Circulation, Definition, Factors, Three Model Cells

Atmospheric Circulation

The large-scale circulation of air around the Earth is known as atmospheric circulation. It is in charge of transporting heat and moisture from the equator to the poles, and it has a significant impact on our weather system. In this article, we will go over atmospheric circulation in-depth, including the tricellular model and how it affects our weather. We’ll also look at some of the variables that affect atmospheric circulation, such as temperature, pressure, and wind speed.

The atmosphere is virtually always in motion. A variety of factors influence the movements of air. While some airflow is weak and brief, some are strong and persistent. Atmospheric motions involve both horizontal and vertical movement. Horizontal air movement is called wind.

On the other hand, small-scale vertical motions are generally referred to as updrafts and downdrafts. Large-scale vertical motions are called ascents and subsidences. More air is involved in the horizontal movements than the vertical ones.

The wind blows in many directions. Wind directions are measured by an instrument called an anemometer. Wind vanes also are used to measure the direction of the flow of current.

Read More: Monsoon in India

Atmospheric Circulation Three Model Cells

Each hemisphere’s Atmospheric Circulation is made up of three cells. The Hadley cell, the Polar cell, and the Ferrel cell are three types of cells. Each circulation cell makes one complete circuit around the Earth each year.

1. The Hadley cell

The Hadley cell is a large-scale atmospheric circulation in which air rises near the equator, flows poleward at a high altitude, descends in the subtropics, and then flows equatorward near the surface.

2. The Ferrel cell

The Ferrel cell is a mid-latitude atmospheric circulation in which air rises in the subtropics, flows poleward at a high altitude, and then descends in the mid-latitudes.

3. Polar Cell

A low-latitude atmospheric circulation in which air rises near the poles flows poleward at a high altitude and descends in the subpolar regions.

The three atmospheric circulation cells are linked. The Hadley cell moves warm air and moisture from the equator to the mid-latitudes, where it contributes to precipitation formation. The Ferrel cell moves cold air from the mid-latitudes to the poles, where it contributes to the formation of sea ice. The Polar cell transports warm air from the poles to the mid-latitudes, where it contributes to precipitation formation.

Read More: Jet Streams

General Atmospheric Circulation

The wind is the result of a pressure gradient, largely caused by the differential heating of the earth. Winds in the atmosphere do not follow the same pattern as we go up in the atmosphere. In fact, winds may change their direction and intensity multiple times within the same day. Largely, wind movement in the atmosphere can be classified into three broad categories:

Read More: Types of Winds

General Atmospheric Circulation Diagram

We are providing with you a General Atmospheric Circulation Diagram below:

Read More: Pressure Belts

Atmospheric Circulation & Direction of Movement of Wind

Insolation is the main cause of wind. All winds originate from the same primary sequence of events. Unequal heating of different parts of the Earth’s surface results in temperature gradients that generate pressure gradients, which set air into motion. The wind is nature’s attempt to even out the uneven air pressure distribution across Earth’s surface. Air generally begins to flow from higher-pressure areas toward lower-pressure areas. However, rotation and friction exist, so this general statement is usually not entirely accurate.

The direction of wind movement is determined principally by the interaction of three factors: the pressure gradient, the Coriolis effect, and friction. The speed of wind flow is determined primarily by the pressure gradient, though the frictional force plays a significant role in slowing down the wind. The air accelerates swiftly if the gradient is steep and the acceleration is slow if the gradient is gentle.

Surface winds are relatively gentle over most of the world most of the time. Wind speed also varies depending on the altitude. It is quite variable from one altitude to another and from time to time. It usually increases with height. Winds tend to move faster above the friction layer.

Read More: List of Major Local Winds

Atmospheric Circulation Factors

1. The Sun

Sun is the ultimate source of all forces that propels wind causing unequal heating of the earth’s surface. This plays a major role in determining the speed and movement of the wind.

2. Pressure Gradient

If there is higher pressure in one area than in another, air will move from the higher pressure toward the lower pressure in response to the pressure gradient force. In other words, the rate of change of pressure with respect to distance is the pressure gradient. The pressure gradient force remains operational from the high-pressure area to the low pressure while causing the wind movement.

The Pressure Gradient is found to be strong when the isobars are close, while the pressure gradient is weak when the isobars are apart. As a closely spaced gradient implies a steeper gradient, this also indicates a greater wind speed. The wind direction follows the direction of change of pressure which is perpendicular to the isobars.

Read More: Atmospheric Pressure

Atmospheric Circulation UPSC

Atmospheric circulation is an important factor in determining a location’s weather conditions. It aids in the exchange of heat and moisture between various parts of the atmosphere. It also has an impact on the distribution of precipitation. A variety of factors influence atmospheric circulation, including temperature and pressure gradients, Coriolis force, and friction. This topic holds immense importance for the UPSC exam and an aspirant should be well aware of this topic.

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