At the surface, air tends to flow outwards in all directions from the center of high pressure and is deflected by the Earth's rotation (see Coriolis effect) to produce a spiral movement. This is why clouds tend to form in spirals or swirls.
The atmosphere is divided into horizontal layers with different temperatures and pressures. The higher up you go, the cooler it gets because there are fewer particles to scatter light. There are also less molecules to collide with for heat absorption so it gets cold faster high up in the atmosphere.
The lowest layer of the atmosphere is called the troposphere. It extends from the ground up to about 10-15 miles (16-24 km). Most weather occurs within this layer. It is thickest near the equator where it can reach 9-10 miles (15-16 km). It thins out the farther you get from the equator heading toward zero at the poles.
Cirrus clouds are formed when water vapor in the air crystalsizes due to low temperatures. This happens when there are not enough molecules for each particle to bond with two others. When this happens, those particles just stay single and don't join together which makes an infinite number of crystals that eventually become clouds.
Wind causes turbulence in the atmosphere which spreads out the clouds.
To eliminate pressure differences and create equilibrium, air always flows from high-pressure zones to low-pressure areas. The rotation of the earth produces a force known as the Coriolis effect, which prevents air from traveling in straight lines. As a result, air moves in spirals.
The direction of the airflow is called the wind speed. It can be either forward or backward relative to your location, depending on whether the pressure is rising or falling behind you.
Low pressure areas tend to be located near coasts or large bodies of water. These locations are where clouds form because water evaporates more easily than air. As the wind passes over the ocean, it picks up moisture from the clouds that form along its path.
High pressure areas are found in middle latitudes between 30 and 60 degrees north and south of the equator. They lead trade winds that blow across large parts of the world's oceans. Without these high-pressure systems, there would be no stable atmosphere for life as we know it!
It is important to remember that the Earth's surface is not smooth but rather full of bumps and holes, some very deep. As a result, air pressures vary greatly across the globe. Air travels from high pressure regions to low pressure regions, filling up the lower pressure areas first and then moving on to higher pressure zones.
The Coriolis force diverts air as it tries to go from high to low pressure in the atmosphere. In the Northern Hemisphere, this means that air is blown anticlockwise around low pressure and clockwise near high pressure. The force acts on all objects moving through the air; clouds, birds, and missiles are all affected by it.
The Coriolis effect was first noticed by French scientists in 1852 and is named after Gaspard Gustave de Coriolis, who proposed it to explain some weather phenomena. He showed that wind patterns are influenced by the rotation of the earth, and not just by temperature differences. Before this discovery, people thought that winds were just random movements of air caused by heat rising or cold falling.
Coriolis discovered that when a mass of air moves towards lower pressure it will be forced backwards (anticlockwise) over northern France, and forwards (clockwise) over southern France. He called this new phenomenon "magnetism of the atmosphere". Today we know that magnetic fields can influence the movement of air but at the time this was very surprising news for scientists.
Winds always try to go from high pressure areas to low pressure ones, so if you block off the path they take, you can use them to guide missiles or bombs away from populated areas.
"The air seeks to go in a straight path from high to low pressure, but because to the Coriolis effect, the air is deflected to the left in the Southern Hemisphere as it moves clockwise towards the low pressure area. In the Northern Hemisphere, it deflects to the right and advances counter-clockwise towards the low pressure zone "McBride says.
Thus, air moves from high pressure areas to low pressure areas.
Also, wind blows where there is movement of air. Where there is high pressure near the surface of the earth, the surrounding air tends to flow upward, creating wind. As the air reaches greater heights, it becomes less dense so it falls back to lower levels. This is why high winds are usually found near the ground - because that's where all the air is moving toward lower densities.
Wind travels in straight lines unless obstructed by physical features such as mountains or valleys. It follows paths of least resistance - which in most cases means it goes where the land uses are flat and there are few obstacles in its way.
Low pressure systems are also called depressions in meteorology. Such systems often develop when cold air is pushed below warmer air of similar density resulting in lower-than-normal pressures at the surface. Colder air is less likely to rise so large regions of low pressure can form without any associated precipitation change. However, if enough moisture is present in the warmer air, rain may fall when the low passes over a water body.
The rotation of the earth causes the Coriolis force. It is in charge of pulling air to the right (counterclockwise) in the Northern Hemisphere and to the left (clockwise) in the Southern Hemisphere. The Coriolis Effect is the observed curved path of moving objects in relation to the Earth's surface. For example, a ball thrown into the wind will curve away from the thrower.
This effect was first noted by Gaspard-Gustave Coriolis and has been confirmed by many studies since then. It can be used to explain many other phenomena related to gravity including: water flowing leftward in a clockwise rotating system; snow falling on mountain peaks; and ships being steered to the right (east) by winds coming from the west (or south).
Coriolis force changes the direction in which objects fall if they are moving. Thus, an object that is moving towards the north would fall toward the east under the influence of this force. This is why buildings in New York City tilt 13 degrees counterclockwise from their geographic location. The same thing happens with vehicles: They would roll down the streets of San Francisco instead of London because the force of the wind would be pushing them to the left (instead of right).
The Coriolis Force explains why there is a constant wind speed over flat land at any given time.
Because of the rotation of the globe, the surface flow within the cells nearest to the equator turns somewhat westward (the Coriolis effect). Air rising near the solar equator sinks about 30 degrees N or S. This is why there are more clouds over the North Pole and less over the South Pole.
The same thing happens near the poles in winter. The surface flow within the cells nearest the poles turns somewhat eastward (the Polar-Coriolis force). So air rising near the Arctic Circle falls toward the Antarctic Plateau and produces snowstorms there.
At both the Arctic and Antarctic circles, there are fewer clouds because there's no wind to blow them around. But there are still large areas of clear sky because there are no surface currents to carry clouds anywhere else.
The reason that there are more clouds over the North Pole and less over the South Pole all year round is due to the fact that there is more ice here to reflect sunlight. More ice means more clouds.
And just to confuse things a bit more, there are also more clouds over high land and less low down. This is because high up there is less heat from the sun and more cold air which makes clouds more likely. Down below it's hot and cloudless.