air curtains
2012-Aug-01, Wednesday 10:04 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
mellowtiggerDid you know that Earth has "stripes" in its atmosphere, like the big planets have? They're related to those air blowers that hang over the gate entrances to some stores. No, really.
Moving air can be used as a barrier to the cross-flow of other air. Air curtains are not as effective as physical doors for separating cold and warm air, but they do actually work nevertheless. It's easy to find descriptions here and there that explain how to configure the air curtain for maximum efficiency. The important thing is that they do have a strong effect.
The region of a planet that directly faces its sun will heat up faster than elsewhere on a planet. The atmosphere there will grow hotter, expand, and rush upward to equalize the air pressure. That one region of updraft is important in setting up cycles of air movement across the rest of the planet. On Earth, our equator is generally the most sunward-facing latitude, and that's where our primary updraft begins. As that air rushes upwards, it does two important things.
First, the air cools as it rises, and that cooling leads to rainfall. On Earth, we call this region of rainfall the Tropics. Generally, this region is where we find our rainforests. That updraft has to go somewhere, but it can go only so high. Eventually it pushes outwards instead. That up-and-out motion sets up the second big effect, because it leads to the necessary down-and-in motion of replacement air.
Second, the updraft feeds a perpetual cycle of rotating air. The air rises at the hottest points along the equator, and it falls around 30 degrees north and south of the equator. On Earth, we call these regions of downward air the Subtropics. Remember that this air previously rained out its moisture at the equator. As it comes down to the ground in the subtropics, the air is very dry. These two regions are where we find our deserts.
This first loop of air current is called a Hadley cell. While its immediate environmental effects are already important, let's consider a consequence of its movement. Remember the air curtain at the store entrance? The downward motion of the air curtain inside the store (the primary loop) leads to a similar downward motion of the air outside the store (a secondary loop). The two loops interact very little, so the air temperatures don't "mix" along their interface.
Earth has these secondary loops too. Each of them is called a mid-latitude cell. They are influenced by the motion of the primary loop, although they are weaker. Those secondary loops influence the creation of even weaker tertiary loops closer to the poles. The interfaces between the different loops have the same effect on Earth as they do at the storefronts. Cold air (farther from the equator) is kept separated from warm air (closer to the equator). This separation is important to global climate change forecasts.
As one science writer points out, if the loop effect is weak, then air mixes much faster between the equator and the poles. That mixing would lead to polar regions experiencing much warmer weather than usual, which would lead to much faster glacier melt than predicted by current models. In fact, much faster melting is exactly what's happening right now in Greenland.
Other news, however, points to a strengthening of the cells. If the cells are expanding their territory range, though, then this change could actually be bad news instead of good. It would fundamentally change the local climates if the air loop interfaces moved to new areas of the planet.
Earth has atmospheric bands like other planets with thick atmospheres, and they're very important to our climate forecast. They are yet another "moving part" to the complicated machinery that have kept our ecosystems in their recent (very enjoyable) state. As you already know, I advocate against tinkering with our biosphere. I commute by bicycle to help reduce my own carbon dioxide addition to our atmosphere, hopefully reducing the impact of humanity's effect on climate change. I hope that education about Earth's complex systems will help encourage other people to consider their personal and collective influence on global climate.
Moving air can be used as a barrier to the cross-flow of other air. Air curtains are not as effective as physical doors for separating cold and warm air, but they do actually work nevertheless. It's easy to find descriptions here and there that explain how to configure the air curtain for maximum efficiency. The important thing is that they do have a strong effect.
The region of a planet that directly faces its sun will heat up faster than elsewhere on a planet. The atmosphere there will grow hotter, expand, and rush upward to equalize the air pressure. That one region of updraft is important in setting up cycles of air movement across the rest of the planet. On Earth, our equator is generally the most sunward-facing latitude, and that's where our primary updraft begins. As that air rushes upwards, it does two important things.
First, the air cools as it rises, and that cooling leads to rainfall. On Earth, we call this region of rainfall the Tropics. Generally, this region is where we find our rainforests. That updraft has to go somewhere, but it can go only so high. Eventually it pushes outwards instead. That up-and-out motion sets up the second big effect, because it leads to the necessary down-and-in motion of replacement air.
Second, the updraft feeds a perpetual cycle of rotating air. The air rises at the hottest points along the equator, and it falls around 30 degrees north and south of the equator. On Earth, we call these regions of downward air the Subtropics. Remember that this air previously rained out its moisture at the equator. As it comes down to the ground in the subtropics, the air is very dry. These two regions are where we find our deserts.
This first loop of air current is called a Hadley cell. While its immediate environmental effects are already important, let's consider a consequence of its movement. Remember the air curtain at the store entrance? The downward motion of the air curtain inside the store (the primary loop) leads to a similar downward motion of the air outside the store (a secondary loop). The two loops interact very little, so the air temperatures don't "mix" along their interface.Earth has these secondary loops too. Each of them is called a mid-latitude cell. They are influenced by the motion of the primary loop, although they are weaker. Those secondary loops influence the creation of even weaker tertiary loops closer to the poles. The interfaces between the different loops have the same effect on Earth as they do at the storefronts. Cold air (farther from the equator) is kept separated from warm air (closer to the equator). This separation is important to global climate change forecasts.
As one science writer points out, if the loop effect is weak, then air mixes much faster between the equator and the poles. That mixing would lead to polar regions experiencing much warmer weather than usual, which would lead to much faster glacier melt than predicted by current models. In fact, much faster melting is exactly what's happening right now in Greenland.
Other news, however, points to a strengthening of the cells. If the cells are expanding their territory range, though, then this change could actually be bad news instead of good. It would fundamentally change the local climates if the air loop interfaces moved to new areas of the planet.
Earth has atmospheric bands like other planets with thick atmospheres, and they're very important to our climate forecast. They are yet another "moving part" to the complicated machinery that have kept our ecosystems in their recent (very enjoyable) state. As you already know, I advocate against tinkering with our biosphere. I commute by bicycle to help reduce my own carbon dioxide addition to our atmosphere, hopefully reducing the impact of humanity's effect on climate change. I hope that education about Earth's complex systems will help encourage other people to consider their personal and collective influence on global climate.