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If we can recall some physics knowledge, heat likes to move from hotter areas to cooler areas. Additionally, matter under high pressure likes to move to areas of lower pressure. In areas of the Earth where the atmosphere is warmer, air will move towards a cooler area. In areas of the Earth where the atmosphere is under high pressure, the air will move towards areas of lower pressure. So what do we call it when air moves again?
Oh right, wind! |
Air moves from hot to cold and high-pressure to low-pressure areas, creating wind |
From the equator, wind travels clockwise to the south and counter-clockwise to the north resulting in winds around the equator always coming from the east! |
Distribution of Wind on EarthThe Earth's wind system is a bit more complex than that though. Beyond differences in northern and southern hemispheres, air travels only a fraction of the distance of that hemisphere in either direction. We have heat-driven movement starting from the equator and pressure-motivated movement from the poles. Each of these only makes it roughly a third of the way towards the other. The section between these major movement areas act like a gear, circulating air between them and in the opposite direction than the surrounding areas.
The area moving air from the equator is called the Hadley Cell or Trade Winds. These are the most active wind areas on the planet, conducive to many a tropical storm. At the equator, however, there is a much quieter band of wind activity aptly named the Doldrums. Wind activity in this area is sparse and inconsistent. There is no prevailing wind direction here. Where the trade winds meet the middle bands in the hemispheres are also particularly wind-deprived areas. These occur at around 30-35 degrees north and south of the equator and are named the Horse Latitudes. |
Wind PhenomenaSpeaking of phenomena, wind can get fairly wild on the Earth. Radical changes in pressure and temperature take make some interesting things happen. Despite these wind activities being destructive, some of them have become things even humans depend on to make normally inhospitable places more hospitable.
HurricanesDepending on where you're from, these can go by a number of names. Severe tropical storms, hurricanes, typhoons, they all describe the same type of wind phenomena, all of them initiating from the band of wind activity originating off of the equator. While it is possible for them to form in a few ways, they generally follow the same life cycle. They start as a tropical disturbance, where thunderstorms begin to develop over the ocean with no major cyclical wind activity. If the storms maintain themselves until a cyclone can stay consistently formed, an "eye" of the storm can form. This phase is called a tropical depression for this eye formation, higher winds concentrating toward that center point of low air pressure.
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Hurricanes can be ridiculously destructive forces when they reach land. |
Tornadoes are a common occurrence in the Great Plains of the United States of America thanks to the wind relationship coming from Canada to the north and the Gulf of Mexico from the south |
When this mesocyclone reaches low enough from the storm, it will pull up dirt and land particles from the ground in the moment we tend to call a "tornado touchdown" (no relation to American football, just the moment the mesocyclone touches the ground from above). From here, the tornado will continue following the path of the storm cloud it formed from, the air inflow from the RFD cooling over time. When this inflow no longer has warm enough air powering the cyclone, the tornado will enter a dissipating phase, breaking into rope-like tendrils that disappear back into the atmosphere. While these are not nearly as large as tropical storms, they can be just as destructive and are also categorized based on this destructive force. The highest classification reaching up to 609 km/h (379mph)!
MonsoonsGrowing up, I always associated rain with a monsoon, but the core of this phenomenon is wind. Despite the destruction this storm can bring, it also enables wet/dry seasonality to normally very dry areas of the world. Even among human populations, we depend on monsoon activity to bring in annual rains for our crops in more tropical areas of the world. Monsoons occur when the prevailing wind direction goes through a seasonal change, moving from cold, high-pressure areas to warmer low-pressure areas. Along with this wind direction shift comes a slew of rainstorms defining the seasons for areas that deal with this annual phenomenon.
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Humanity, while we might not always realize the effects of our activities over time, have caused significant shifts in both of the properties we went over earlier: atmospheric heat and pressure. By emitting a bunch of carbon dioxide into the atmosphere much faster than geologic time has historically allowed and the planet's organisms have adapted to, we have both modified atmospheric pressure and the heat the Earth is exposed to from the sun. Local wind phenomena have become less predictable and more chaotic as a result. The general rules that we discussed above become more malleable over time, changing how the planet's wind system acts.
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Human emissions alter atmospheric heat and pressure causing the balance of Earth's wind system to shift |
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