# The circulation of the atmosphere

The atmosphere is the layer of gases that surrounds the Earth and that, thanks to its low density, can easily move over its surface. As with all gases, the air changes its density as a function of temperature and this makes it possible to rise and fall.

Since there are constant temperature variations between some points and others on Earth, the air is in continuous motion. Its ascent or descent is not carried out in a straight line, and this causes the winds. In addition, the water vapor it contains becomes liquid (condenses) as it rises to colder layers, so precipitation occurs.

## The heat

The energy of the Sun that passes through the Earth's atmosphere warms it. But upon reaching the earth's surface it can be found with water or with rock, depending on whether it falls on the sea or a continent. Rock has a tendency to heat and cool faster than water. Therefore, the continents cool and heat before the oceans, creating zones with different temperatures.

The amount of energy that each portion of the Earth receives also depends on the inclination of the sun's rays, the more vertical, the more energy. Therefore, the regions near the poles are much colder than those near the equator. In addition, in the northern hemisphere the proportion of emerged lands is much higher than in the south.

## Latitude and altitude

Latitude determines the position of a given point on Earth in relation to the equator. It is measured by dividing the hypothetical terrestrial quadrant into 90 parallels, each of which corresponds to a degree of the right angle. The equator has latitude 0º and the poles, 90º. As stated, high latitudes receive much less heat than low latitudes.

Altitude refers to the height of a given point in relation to sea level. As the altitude increases, the density of the atmosphere decreases and, therefore, its ability to absorb heat. Therefore, the higher a place is, the lower the temperature will be.

## Moving air

Because of the differences between water and land, latitude and altitude, areas are created in which warmer and lighter air tends to rise, while heavier and colder air drops. These pressure differences are the cause of the winds.

But it has been observed that the atmosphere follows a more or less regular movement called general circulation, because there are areas of the planet with characteristic conditions. Along the equator there is a zone of low pressures, then two subtropical zones with high pressures, two temperate zones of low pressure and, finally, the polar zones, again, with high pressures. The air masses move between these areas with different pressures.

## Earth's rotation

The earth, when turning on its axis, produces centrifugal and inertial forces that drag the air. In addition, when in contact with the surface, friction forces also originate. All these forces have a huge influence on the way the air moves.

When, due to pressure differences, the air starts to move, the rotation of the Earth deflects it according to the direction of travel: to the right in the northern hemisphere and to the left in the southern hemisphere. This whole complex system of forces causes the wind to travel describing wide circles or spirals.

Is called Coriolis force to the inertia that acts on a body or mass of air because of the rotation of the Earth. For example, trade winds and west originate because of the strength of Coriolis.

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