Monday, September 17, 2007
WIND
by Peter Bowyer, Meteorologist, Nova Scotia, Canada
Have you ever gone to the beach on a nice summer's day and noticed the pleasant wind that develops from over the water about mid-morning? If you have, then you have experienced one of the simplest, and oldest known negative feedback mechanisms in the atmosphere--the sea breeze.
The sea breeze results from the land heating up more rapidly than the water on sunny days. The heated air over the land becomes more buoyant and rises to a higher elevation. Since there is now more air aloft over the land than at the same elevation just offshore, there is a pressure build-up. Similarly, at the surface, the pressure over the land has dropped relative to just offshore because the rising air has created a slight vacuum. The overall effect is a small circulation of air which brings cooler marine air over the land, thereby moderating the temperature difference which started the whole process in the first place. This is called a negative feedback mechanism.
The atmosphere obeys the basic rules of physics such as Newton's second law of thermodynamics. This law states that all natural systems move toward increasing disorder--in other words, they must wind down. Meteorologists observe this daily as the earth's surface, heated unevenly by the sun, produces hot and cold spots and thus differences in atmospheric pressure. The fun begins when forecasters try to figure out how the atmosphere will adapt to Newton's law. Wind is the result of differences in pressure--the result of the atmosphere trying to "smooth things out" once again. The stronger the pressure difference, the stronger the wind. Even on the large scale, however, it is not unlike the idea of the sea breeze. Air is shunted across the earth's surface in order to even out the temperatures: hot air moves north and cold air heads south. In mid-latitudes, such as Canada and the U.S., this movement of air happens in the form of high and low pressure areas which you hear your local forecaster referring to.
The highs and lows, however, are just the "big-picture." The more interesting things happen on a smaller scale where Newton's second law still applies. Besides the strength of the pressure pattern, the wind is also very dependent on other factors such as pressure changes, friction (roughness of the earth's surfact), turning effects and stability (how bouyant the air is). Let us take a quick look at each of these.
The frictional force acts to slow the wind down. Fortunately, as the wind gets stronger, the frictional force gets stronger--causing the wind to slow down. It would be very difficult to live in a world where the wind just kept getting stronger. Over the sea, waves are generated by wind. As the wind picks up, the waves get higher, causing more drag on the wind, thereby slowing it down, allowing the waves to decrease slightly. This all happens quickly such that a balance is soon established. The main point is that friction is a limiting force in regard to wind systems.
High pressure areas are accompanied by anticyclonic winds--winds that travel clockwise (in the northernm Hemisphere) around the high. When winds turn anticyclonically, this results in a boosting effect that must be added to the pressure wind. Fortunately, as winds become more anticyclonic, the pressure pattern must weaken in order for other atmospheric balances to be maintained. This means that the boosting effect will be added to a smaller wind to start with.
Low pressure areas, on the other hand, are acoompanied by cyclonic winds--winds that travel counter-clockwise around the low. Winds turning in this fashion result in a diminishing effect which must be subtracted from the pressure wind. Fortunately, storm systems are cyclonic, meaning that although there may be a very strong pressure wind, there is also a limiting effect due to the turning of the wind. In most storm systems, the strongest pressure wind is just to the left of the storm's track--Fortunately, the strongest cyclonic effects occur at this same place. Were this not the case, many of our winter storms would be packing hurricane force winds.
Not only does the wind result from pressure differences, but it also is affected by changes in the pressure pattern. These changes have to be significant in order for them to have any measurable impact--and this is the case in rapidly moving or intensifying storms. These pressure change effects can either add to, or subtract from, the pressure wind. Fortunately, they subtract from the wind in storms just to the left of the storm's track where the pressure wind is high. As well, the place where they add the most is fortunately in a place where atmospheric stability is greatest--just to the right of the storm's track. Stability helps to keep the winds diminished, so a boosting effect here is not as bad as it could be. Countless times I have heard forecasters express an appreciation to Mother Nature for being forgiving in the way she balances forces. If the forces were to balance the other way, we would likely be unable to tolerate living in such a harsh climate.
As a Christian and an admirer of the Master's handiwork, I see no coincidence or fortune in any of this. What I do see is design. And where there is a design there is a designer. If we look at the world with truly objective eyes, we will clearly see the hand of the Maker. Just as Paul said,
For since the creation of the world, God's invisible qualities--his eternal power and
divine nature--have been clearly seen, being understood from what has been made,
so that men are without excuse. (Romans 1:20)
Dandy Designs, May/June, 1994
Cora Gail Trent
www.cgtrent.com
cgtrent@att.net
The sea breeze results from the land heating up more rapidly than the water on sunny days. The heated air over the land becomes more buoyant and rises to a higher elevation. Since there is now more air aloft over the land than at the same elevation just offshore, there is a pressure build-up. Similarly, at the surface, the pressure over the land has dropped relative to just offshore because the rising air has created a slight vacuum. The overall effect is a small circulation of air which brings cooler marine air over the land, thereby moderating the temperature difference which started the whole process in the first place. This is called a negative feedback mechanism.
The atmosphere obeys the basic rules of physics such as Newton's second law of thermodynamics. This law states that all natural systems move toward increasing disorder--in other words, they must wind down. Meteorologists observe this daily as the earth's surface, heated unevenly by the sun, produces hot and cold spots and thus differences in atmospheric pressure. The fun begins when forecasters try to figure out how the atmosphere will adapt to Newton's law. Wind is the result of differences in pressure--the result of the atmosphere trying to "smooth things out" once again. The stronger the pressure difference, the stronger the wind. Even on the large scale, however, it is not unlike the idea of the sea breeze. Air is shunted across the earth's surface in order to even out the temperatures: hot air moves north and cold air heads south. In mid-latitudes, such as Canada and the U.S., this movement of air happens in the form of high and low pressure areas which you hear your local forecaster referring to.
The highs and lows, however, are just the "big-picture." The more interesting things happen on a smaller scale where Newton's second law still applies. Besides the strength of the pressure pattern, the wind is also very dependent on other factors such as pressure changes, friction (roughness of the earth's surfact), turning effects and stability (how bouyant the air is). Let us take a quick look at each of these.
The frictional force acts to slow the wind down. Fortunately, as the wind gets stronger, the frictional force gets stronger--causing the wind to slow down. It would be very difficult to live in a world where the wind just kept getting stronger. Over the sea, waves are generated by wind. As the wind picks up, the waves get higher, causing more drag on the wind, thereby slowing it down, allowing the waves to decrease slightly. This all happens quickly such that a balance is soon established. The main point is that friction is a limiting force in regard to wind systems.
High pressure areas are accompanied by anticyclonic winds--winds that travel clockwise (in the northernm Hemisphere) around the high. When winds turn anticyclonically, this results in a boosting effect that must be added to the pressure wind. Fortunately, as winds become more anticyclonic, the pressure pattern must weaken in order for other atmospheric balances to be maintained. This means that the boosting effect will be added to a smaller wind to start with.
Low pressure areas, on the other hand, are acoompanied by cyclonic winds--winds that travel counter-clockwise around the low. Winds turning in this fashion result in a diminishing effect which must be subtracted from the pressure wind. Fortunately, storm systems are cyclonic, meaning that although there may be a very strong pressure wind, there is also a limiting effect due to the turning of the wind. In most storm systems, the strongest pressure wind is just to the left of the storm's track--Fortunately, the strongest cyclonic effects occur at this same place. Were this not the case, many of our winter storms would be packing hurricane force winds.
Not only does the wind result from pressure differences, but it also is affected by changes in the pressure pattern. These changes have to be significant in order for them to have any measurable impact--and this is the case in rapidly moving or intensifying storms. These pressure change effects can either add to, or subtract from, the pressure wind. Fortunately, they subtract from the wind in storms just to the left of the storm's track where the pressure wind is high. As well, the place where they add the most is fortunately in a place where atmospheric stability is greatest--just to the right of the storm's track. Stability helps to keep the winds diminished, so a boosting effect here is not as bad as it could be. Countless times I have heard forecasters express an appreciation to Mother Nature for being forgiving in the way she balances forces. If the forces were to balance the other way, we would likely be unable to tolerate living in such a harsh climate.
As a Christian and an admirer of the Master's handiwork, I see no coincidence or fortune in any of this. What I do see is design. And where there is a design there is a designer. If we look at the world with truly objective eyes, we will clearly see the hand of the Maker. Just as Paul said,
For since the creation of the world, God's invisible qualities--his eternal power and
divine nature--have been clearly seen, being understood from what has been made,
so that men are without excuse. (Romans 1:20)
Dandy Designs, May/June, 1994
Cora Gail Trent
www.cgtrent.com
cgtrent@att.net
