Atmospheric Circulation

Let’s discuss atmospheric circulation in detail.

Solar radiation hits the surface through the atmosphere, where it is absorbed or reflected by the atmosphere and the earth’s surface. The majority of this absorption takes place on the earth’s surface, raising the temperature of both land and sea. Conduction, the process of molecules colliding and transferring energy, transfers a little heat from the surface in the first few centimetres of the atmosphere. Because air molecules are wider apart than those in liquids or solids, they do not collide as frequently as they do in liquids or solids, making the air a poor heat conductor. Radiation and convection convey the majority of heat in the atmospheric circulation.

General Circulation of the Atmosphere

The following are the terms included in the general circulation of the atmosphere:

• Energy balance
• Transport processes
• The three-cell model

1. Energy Balance

This is associated with the ratio of inbound solar radiation and outgoing earth radiation emitted by the earth. When averaged over a year, the global energy balance is nearly balanced (incoming equals outgoing). Because outgoing terrestrial radiation is more than absorbed solar radiation, incoming radiation is a surplus in the tropics and a deficit in the polar regions when averaged over a latitude band.

2. Transport Process

During atmospheric circulation, atmospheric and marine transport processes distribute energy evenly over the globe to compensate for radiation surpluses and deficits in different parts of the world. Atmospheric winds and ocean currents are responsible for this transportation.

3. Three Cell Model

This model is used to describe the energy movement in the atmosphere and depicts the average atmospheric circulation.

The Tricellular Model

The sun is the primary controller of the earth and its atmosphere, and together they form an interconnected global system that leads to atmospheric circulation. The tricellular model of atmospheric circulation within this global system causes various climates in different places. The difference in temperature between equatorial and polar regions, which is generated by the distance from the sun and the amount of atmosphere travelled through, is the cause of these atmospheric motions.

The tricellular model of atmospheric circulation is made up of three air masses that influence atmospheric movement and heat energy redistribution. Starting at the equator, the Hadley cell, Ferrel cell, and Polar cell are the three air masses.

The ITCZ (Intertropical convergence zone), where the trade winds from the northern and southern hemispheres meet, is also included in the tricellular model. The ITCZ is a low-pressure area where convection currents compel the trade winds to climb after picking up latent heat as they traverse oceans. Rising convection currents are then adiabatically cooled, resulting in colossal cumulonimbus clouds.

The basic elements of this tricellular model of atmospheric circulation include:

• The Inter-Tropical Convergence Zone is formed due to severe heating at the equator, which results in low pressure and the formation of a belt of clouds in an area known as the Doldrums (ITCZ).

• Air rising in this zone begins to drift to higher latitudes where it is cooler in an attempt to equalise temperature differences, but it cools and becomes denser in the process, pushing it to sink around roughly 30 degrees North and South of the equator.

• Due to pressure gradient differences, the sinking air travels laterally back towards the equator, completing the initial loop (air moving from higher to lower pressure areas). This is referred to as the Hadley cell.
• Some sinking air continues northwards towards the poles until it reaches 60 degrees N and S, where it collides with even colder polar air travelling south (in the Northern Hemisphere). The warmer air from the tropics rises over the cold air at a meeting known as a front due to temperature differences. Some of this rising air returns to the equator, cooling and sinking around roughly 30 degrees N and S, finishing the second loop, known as the Ferrell cell.
• Meanwhile, frigid polar air travelling laterally across the ground towards lower latitudes heats up and rises to 60 degrees at the Ferrel cell’s pole-ward border. This warmer air begins to travel to higher latitudes again at a certain altitude, until it cools and sinks near the poles, completing the Polar cell.

Conclusion

Even when weather fronts and storms cause disturbances, the movement of air around our planet’s atmosphere follows a predictable pattern. Because the sun heats the earth more at the equator than at the poles, this pattern is known as atmospheric circulation. It’s also influenced by the earth’s rotation. The unequal distribution of land and sea masses on the planet, as well as the rotation of the earth on its axis, all contribute to atmospheric circulation.