How does atmospheric pressure affect wind direction? | Socratic
Weather is the current state of the atmosphere and is determined by factors like temperature, pressure and humidity. These factors that cause. Air pressure can simply be measured with a barometer by measuring how An Ideal Gas behaves in such a way that the relationship between pressure . retard the motion of the wind -- it is always in the direction opposite the wind velocity. To get wind there needs to be a pressure gradient, so one side will have a higher pressure than the other. Wind will then start blowing from the.
He was one of the first explorers to use this feature of the climate system to his advantage, or at least, the first to make it well known: As more and more ships made the journey across the Atlantic Ocean to the Caribbean islands to bring back spices and other merchandise, these consistent winds came to be known as the "trade winds. Fifty years after Columbus returned from his first voyage, inCopernicus published his heliocentric model of the solar systemwhere a rotating Earth traveled around the sun.
Since the planet spins towards the east, this would cause the winds to appear to blow the opposite direction — from east to west. Observed versus predicted winds based on Earth's rotation. About 70 years later, several scientists converged on similar explanations for the trade winds. At a meeting of the Royal Society of London inEdmond Halley, an English physicist and astronomer, proposed that the trade winds arose from intense solar heating of the tropics Halley, Halley thought that heated air would follow the sun during the day, which would pull it from east to west to form the trade winds.
He compiled and described wind directions from different regions, invoked the idea that heated air expands, and portrayed his ideas in a map, shown in Figure 5.
Halley was onto something. As explained above, the tropics do receive intense solar radiation. This energy heats the surface and the air right above it, and because hot air is less dense than cold air, it rises into the atmosphere. But Halley and others in the Royal Society still had a hard time developing a convincing explanation for why the trade winds blow from the northeast in the northern hemisphere and the southeast in the southern hemisphere, not just straight east to west.
Half a century later, an English meteorologist named George Hadley proposed a new idea in a paper in the Philosophical Transactions Hadley, Hadley made use of this and other accounts, and conducted a thought experimentfirst imagining how air would circulate when heated by the sun on a non-rotating Earth.
He described how, if the sun-heated air rose over the tropics, air would flow in to fill the void. This air would come from both the north and the south and flow towards the equator, creating large convection cells in which heated air rose at the tropics, flowed north towards the pole as it cooled, then sank and flowed south to replace the rising air see Figure 6. Then, in his thought experimenthe set the Earth in motion, and imagined how these convection cells would be affected.
Then he carefully described how a point on the surface of the Earth and the air above it at the equator had to travel farther than a point at any other latitude as the Earth rotated, and therefore was also traveling faster. Why is this the case? However, the distance each point has to travel to complete that rotation depends on its latitude.
At the equator, a point on the surface travels the farthest to complete a single rotation, while near the poles, a point on the surface hardly moves at all. Thus, the speed at which a point on the surface rotates depends on its latitude see Figure 7. Hadley reasoned that, as high-latitude air flowed toward the equator to replace rising air heated by the sun, the faster-turning tropics would rotate out from underneath it. From the surface, this would make it appear as though this flow of air was deflected to the west.
In other words, surface air would blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere. Using the same logic, Hadley accounted for the westerlies that occur to the north and south of the band of easterlies, or trade winds. The westerlies began, he noted, at the latitude where the heated air that had risen from near the equator had cooled enough to sink back down towards the surface. Because this air was now moving faster than Earth beneath it, as it moved northward it would be deflected to the east see Figure 7.
Today, we know the concept that Hadley described as the Coriolis effectnamed after French mathematician and engineer Gaspard-Gustave de Coriolis, who published a paper in describing energy and apparent motion in waterwheels and other rotating machines Coriolis, Comprehension Checkpoint Christopher Columbus was the first person to suggest that trade winds were caused by Earth's rotation.
5. Atmospheric Pressure & Wind
These calm conditions occur where the trade winds from the Northern and Southern Hemispheres converge and rise — that produces little wind at the surface and a zone of low pressure. As this air rises and cools, the water vapor condenses, creating a persistent band of clouds and intense rainfall that is easily visible in satellite images of Earth, especially over the Pacific Ocean see Figure 8 for an example.
Today, meteorologists and climate scientists call this band of little wind, heavy rain, and low pressure the Intertropical Convergence Zoneabbreviated as ITCZ. At that altitude, the rising air diverges, with some flowing northeast and some flowing southeast deflected from straight north and south by the Coriolis effectfollowing the tropopause while it cools and begins to sink.
Windy Weather II: The Correlation Between Barometric Pressure and Wind Velocity
Exactly opposite to the ITCZ, these two latitude bands are regions of high pressure since the air is descending and very dry conditions, since the air contains very little water vapor.
When the descending air reaches the surface, it again diverges, with some flowing back towards the equator as the trade winds, picking up moisture as it warms, and some flowing towards higher latitudes as the westerlies.
A diagram showing the relationship between the Hadley cell and continental climate. Note that the altitude of the tropopause is higher over the equator than over the poles, and the altitude is greatly exaggerated compared to the diameter of Earth.
The deepest green color in the satellite images indicates dense vegetation, the Congo rainforest, which receives the heavy precipitation within the ITCZ. Comprehension Checkpoint What did sailors call the stretch of ocean between 5 degrees N and 5 degrees S where their sails caught little wind? But while Hadley briefly mentioned why the westerlies might occur, he did not fully explain them — and in fact, they are a bit more difficult to explain.
An important contributor to this effort was Matthew Fontaine Maury, who compiled data on the speed and direction of wind and currents from sailors and scientific organizations around the world, and published his compilation in Maury, The primary object… was to collect the experience of every navigator as to the winds and currents of the ocean, to discuss his observations upon them, and then to present the world with the results on charts for the improvement of commerce and navigation.
Ferrel was a schoolteacher in Nashville, Tennessee, who was unsatisfied with the explanations that other scientists had developed for the winds.
This sinking at the poles drives circulation in the polar cells, which operate over the Arctic and Antarctic regions.
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The Coriolis effect deflects the flowing air to the west, creating bands of polar easterlies. Both the north and south poles are regions of high pressure with little precipitation. You might be used to thinking of the south pole on Antarctica as a snowy place, but the average annual precipitation is 4. But viewed in the context of the Hadley and polar cells, the winds in this region began to make sense.
Wind & Air Pressure
This mid-latitude circulation cell is now called the Ferrel cell after the schoolteacher who first described it. Instead, the westerly flow of air breaks up into a series of eddies, swirls of air whose movement does not match the overall westerly flow see Figure 8, and the animation in Figure 9. These eddies mix the mid-latitude atmosphere and transport heat from the tropics toward the poles; they also produce the mid-latitude storms that roll across weather radars, bringing strong winds and bouts of rain and snow.
The animation below shows how all of these cells interact to produce what we see on the surface: Just like an acrobat with two people stacked on his shoulders would want to move to where there wasn't so much pressure on him, air moves from areas where the pressure is higher to where it is lower.
What causes Air Pressure? Air pressure depends on the density of the air, or how close together its molecules are. You know that a hard rubber ball is more dense than a Styrofoam ball and that ice cream is more dense than whipped cream. Air lower in the atmosphere is more dense than air above, so air pressure down low is greater than air pressure higher up.
Remember those acrobats; there's a lot more pressure on the one on bottom than on the one on top. Temperature also makes changes in air pressure. In cold air, the molecules are more closely packed together than in warm air, so cold air is more dense than warm air. Rising and Sinking Air Since warm air is less dense and creates less air pressure, it will rise; cold air is denser and creates greater air pressure, and so it will sink.
When warm air rises, cooler air will often move in to replace it, so wind often moves from areas where it's colder to areas where it's warmer. The greater the difference between the high and low pressure or the shorter the distance between the high and low pressure areas, the faster the wind will blow.
Wind also blows faster if there's nothing in its way, so winds are usually stronger over oceans or flat ground. Meteorologists can forecast the speed and direction of wind by measuring air pressure with a barometer. Wind Direction Although wind blows from areas of high pressure to areas of low pressure, it doesn't blow in a straight line. That's because the earth is rotating.