Linda holds both a B.S. in Earth Science and M.A. in Geography from the University of Arkansas. She has extensive research experience in Environmental Dynamics, with an emphasis in environmental conservation, ecological anthropology, remote sensing, and plant taxonomy. Linda has 20 years of experience in the field and has taught college level classes in environmental science and physical geography.
Introduction to Anticyclones
You know those really nice days when there isn't a cloud in the sky? Those kinds of days feel sunny and warm outside with no wind blowing, and all you want to do is spend your day outside walking your dog or going to the park. You experience this type of weather when high pressure, or an anticyclone, has set up over the area where you live. But what causes this type of weather to develop?
Because the atmosphere is constantly moving and mixing, it experiences differences in temperature and composition. These result in changes in pressure. Atmospheric pressure can be thought of as the weight of the air piled above. The higher the air is piled up, the greater the pressure. An anticyclone, or high pressure area, is associated with sinking air that results in fair and dry weather. It is caused by several things working together, including wind, the pressure gradient force, the Coriolis Effect, and friction.
The first factor, wind, is when air moves horizontally from place to place. Where air moves too is caused by differences in atmospheric pressure. A good way to understand wind flow is to picture air pressure on a map. Areas of high pressure are like mountains and areas of low pressure are like valleys. The air movement, or wind, goes from high pressure to low pressure. So if you think about it like elevation, the wind blows from the high pressure at the top of the 'mountain' to the low pressure in the 'valley.'
This is what creates wind, and the mechanism that causes it to happen is the second factor in the development of anticyclones. This factor is called the pressure gradient force, or the movement of air from high to low pressure. This is what makes air move from the center of an anticyclone, outward.
Wind high above the surface of the earth has nothing in its way to prevent it moving in a straight line, except for what's known as the Coriolis Effect. Because Earth rotates from west to east, any object that is moving along in a straight line appears to deflect to the right in the Northern Hemisphere. For example, if you're standing at the North Pole and fire a rocket toward Texas, it would actually land to the west of Texas, maybe in California. That is because while the rocket was in the air, the earth rotated beneath it. From your perspective at the North Pole, it would look like your rocket drifted to the right in an arced pathway. Any object in the Northern Hemisphere appears to go in an arc to the right. The Southern Hemisphere is a mirror image of the north and movements are opposite, so everything appears to veer to the left. The Coriolis Effect is what causes air to spin to the right around a high pressure system in the Northern Hemisphere.
The final factor in the formation of an anticyclone is friction. In the lower atmosphere, wind drags across the ground, and the influence of the Coriolis Effect is reduced. This means that the air on the surface doesn't arc to the right as much. The result is that the wind ends up flowing in a clockwise circle around an anticyclone.
Characteristics of Anticyclones
Now that you know how anticyclones develop, how exactly do they affect the weather? The weather under an anticyclone is almost always clear, warm, and calm. There are rarely any clouds or rain, it is sunny, and there is very little wind. Both in winter and summer this is the case. Sunny, warm, nice days happen when an anticyclone, or high-pressure system, moves into your area. The reason for this is that air has piled up high in the atmosphere and the weight of this air is pushing down toward the surface, or sinking. Clouds and thunderstorms that lead to unfavorable weather form when air is able to rise from the ground to above the freezing level in the atmosphere. The sinking of air in an anticyclone prevents this from happening, and nice weather prevails. An anticyclone can bring you nice weather for a few days or even weeks until, eventually, a cold front overcomes it and moves in with clouds or rain.
An anticyclone is a high-pressure area that produces warm, sunny weather. Four factors together result in anticyclone development. The first is wind, or the horizontal movement of air. Second is the pressure gradient force, or the movement of air from high to low pressure. Third is the Coriolis Effect. This phenomenon occurs because of Earth's rotation. Any time an object or air is moving above the surface, Earth rotates beneath it, making it appear to arc to the right in the Northern Hemisphere instead of going in a straight line. The fourth is friction. As wind drags across the surface, it lessens the Coriolis Effect and causes an anticyclone to rotate clockwise.
The importance of anticyclones is how they affect the weather. With high pressure, air has piled up high in the atmosphere and is pushing or sinking down toward the surface. This stops air from rising to create clouds or storms, and it creates warm, sunny weather with no clouds or wind.
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