How Does Changing Air Pressure Affect The Movement Of Air Masses

Lesson Objectives

List the properties of the air currents within a convection cell.
Draw how high and low pressure level cells create local winds and explicate how several types of local winds class.
Discuss how global convection cells lead to the global wind belts.

Vocabulary

advection
Chinook winds (Foehn winds)
haboob
high pressure zone
jet stream
katabatic winds
state cakewalk
depression pressure zone
monsoon
mountain cakewalk
polar front
rainshadow effect
Santa Ana winds
sea breeze
valley breeze

Introduction

A few bones principles go a long mode toward explaining how and why air moves: Warm air rise creates a low pressure zone at the ground. Air from the surrounding area is sucked into the space left by the rising air. Air flows horizontally at top of the troposphere; horizontal menses is called advection. The air cools until it descends. Where it reaches the ground, it creates a high pressure zone. Air flowing from areas of high pressure to low pressure creates winds. Warm air can hold more moisture than cold air. Air moving at the bases of the 3 major convection cells in each hemisphere north and due south of the equator creates the global wind belts.

Air Pressure and Winds

Within the troposphere are convection cells (Effigy below).

Warm air rises, creating a low pressure zone; cool air sinks, creating a high pressure zone.

Air that moves horizontally between high and depression pressure zones makes air current. The greater the pressure deviation between the pressure zones the faster the air current moves.

Convection in the atmosphere creates the planet's conditions. When warm air rises and cools in a low force per unit area zone, information technology may not be able to hold all the h2o it contains as vapor. Some water vapor may condense to course clouds or precipitation. When cool air descends, it warms. Since information technology can then hold more moisture, the descending air volition evaporate water on the footing.

Air moving between large high and low force per unit area systems creates the global current of air belts that profoundly affect regional climate. Smaller pressure systems create localized winds that touch on the conditions and climate of a local area.

An online guide to air pressure and winds from the University of Illinois is institute hither: http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/domicile.rxml.

Local Winds

Local winds event from air moving between small low and high pressure systems. High and low pressure cells are created past a variety of conditions. Some local winds take very important effects on the weather and climate of some regions.

Land and Ocean Breezes

Since water has a very high specific heat, it maintains its temperature well. So water heats and cools more slowly than land. If there is a large temperature difference between the surface of the ocean (or a big lake) and the country next to it, high and low pressure regions form. This creates local winds.

Body of water breezes blow from the cooler ocean over the warmer country in summertime (Figure below). Where is the loftier pressure zone and where is the low pressure zone? Body of water breezes blow at about x to twenty km (6 to 12 miles) per hour and lower air temperature much as 5 to 10°C (9 to 18°F).
Land breezes blow from the state to the sea in wintertime. Where is the loftier pressure zone and where is the low force per unit area zone? Some warmer air from the bounding main rises and then sinks on land, causing the temperature over the country to go warmer.

How do bounding main and country breezes moderate coastal climates?

Land and sea breezes create the pleasant climate for which Southern California is known. The effect of land and sea breezes are felt only about l to 100 km (30 to lx miles) inland. This same cooling and warming upshot occurs to a smaller caste during solar day and nighttime, because land warms and cools faster than the sea.

Monsoon Winds

Monsoon winds are larger scale versions of country and sea breezes; they accident from the sea onto the land in summertime and from the land onto the ocean in winter. Monsoon winds are occur where very hot summertime lands are side by side to the body of water. Thunderstorms are common during monsoons (Figure below).

In the southwestern United States relatively cool moist air sucked in from the Gulf of Mexico and the Gulf of California meets air that has been heated past scorching desert temperatures.

The most important monsoon in the world occurs each year over the Indian subcontinent. More than ii billion residents of India and southeastern Asia depend on monsoon rains for their drinking and irrigation h2o. Back in the days of sailing ships, seasonal shifts in the monsoon winds carried appurtenances back and forth betwixt India and Africa.

Mountain and Valley Breezes

Temperature differences between mountains and valleys create mountain and valley breezes. During the solar day, air on mountain slopes is heated more than air at the same elevation over an adjacent valley. Equally the solar day progresses, warm air rises and draws the cool air up from the valley, creating a valley breeze. At dark the mount slopes cool more quickly than the nearby valley, which causes a mountain breeze to flow downhill.

Katabatic Winds

Katabatic winds move up and downwards slopes, simply they are stronger mountain and valley breezes. Katabatic winds form over a high land area, like a high plateau. The plateau is usually surrounded on about all sides past mountains. In winter, the plateau grows cold. The air above the plateau grows cold and sinks downward from the plateau through gaps in the mountains. Current of air speeds depend on the difference in air pressure over the plateau and over the surroundings. Katabatic winds form over many continental areas. Extremely cold katabatic winds blow over Antarctica and Greenland.

Chinook Winds (Foehn Winds)

Chinook winds (or Foehn winds) develop when air is forced up over a mountain range. This takes identify, for example, when the westerly winds bring air from the Pacific Ocean over the Sierra Nevada Mountains in California. As the relatively warm, moist air rises over the windward side of the mountains, it cools and contracts. If the air is humid, it may class clouds and drop pelting or snowfall. When the air sinks on the leeward side of the mountains, it forms a loftier pressure zone. The windward side of a mountain range is the side that receives the air current; the leeward side is the side where air sinks.

The descending air warms and creates potent, dry winds. Chinook winds can raise temperatures more than 20°C (36°F) in an hour and they rapidly decrease humidity. Snow on the leeward side of the mountain disappears melts quickly. If precipitation falls as the air rises over the mountains, the air volition be dry as it sinks on the leeward size. This dry, sinking air causes a rainshadow effect (Effigy below), which creates many of the world's deserts.

As air rises over a mountain information technology cools and loses moisture, then warms by compression on the leeward side. The resulting warm and dry winds are Chinook winds. The leeward side of the mountain experiences rainshadow effect.

Santa Ana Winds

Santa Ana winds are created in the late fall and winter when the Cracking Basin east of the Sierra Nevada cools, creating a high pressure zone. The loftier pressure level forces winds downhill and in a clockwise direction (because of Coriolis). The air pressure rises, so temperature rises and humidity falls. The winds accident across the Southwestern deserts and so race downhill and westward toward the sea. Air is forced through canyons cutting the San Gabriel and San Bernardino mountains (Effigy below).

The winds are especially fast through Santa Ana Canyon, for which they are named. Santa Ana winds blow dust and smoke due west over the Pacific from Southern California.

The Santa Ana winds often get in at the cease of California'south long summer drought season. The hot, dry winds dry out the landscape even more. If a burn down starts, it tin spread quickly, causing large-scale devastation (Effigy below).

In Oct 2007, Santa Ana winds fueled many fires that together burned 426,000 acres of wild land and more than 1,500 homes in Southern California.

Desert Winds

High summer temperatures on the desert create high winds, which are oft associated with monsoon storms. Desert winds pick up dust because at that place is non as much vegetation to agree downward the dirt and sand. (Figure below). A haboob forms in the downdrafts on the forepart of a thunderstorm.

A haboob in the Phoenix metropolitan expanse, Arizona.

Dust devils, as well called whirlwinds, class as the ground becomes so hot that the air above information technology heats and rises. Air flows into the low pressure and begins to spin. Grit devils are small and brusk-lived but they may cause impairment.

Atmospheric Circulation

Because more solar free energy hits the equator, the air warms and forms a low pressure level zone. At the elevation of the troposphere, one-half moves toward the North Pole and half toward the South Pole. As it moves along the top of the troposphere it cools. The absurd air is dense and when it reaches a high pressure zone it sinks to the ground. The air is sucked back toward the low pressure at the equator. This describes the convection cells n and south of the equator.

If the Earth did not rotate, there would exist 1 convection cell in the northern hemisphere and one in the southern with the rising air at the equator and the sinking air at each pole. But because the planet does rotate, the situation is more complicated. The planet's rotation means that the Coriolis Consequence must be taken into account. Coriolis Effect was described in the Earth'due south Oceans affiliate.

Allow'south look at atmospheric circulation in the Northern Hemisphere every bit a effect of the Coriolis Result (Figure below). Air rises at the equator, but as it moves toward the pole at the top of the troposphere, it deflects to the right. (Recollect that it merely appears to deflect to the correct because the basis below it moves.) At about 30°N latitude, the air from the equator meets air flowing toward the equator from the higher latitudes. This air is cool because it has come from higher latitudes. Both batches of air descend, creating a high pressure zone. One time on the ground, the air returns to the equator. This convection jail cell is called the Hadley Prison cell and is constitute between 0° and thirty°N.

The atmospheric circulation cells, showing management of winds at Globe's surface.

There are 2 more convection cells in the Northern Hemisphere. The Ferrell prison cell is between 30°N and 50° to 60°N. This cell shares its southern, descending side with the Hadley cell to its south. Its northern rising limb is shared with the Polar cell located betwixt 50°Northward to 60°Due north and the North Pole, where common cold air descends.

There are three mirror paradigm circulation cells in the Southern Hemisphere. In that hemisphere, the Coriolis Consequence makes objects appear to deflect to the left.

Global Air current Belts

Global winds blow in belts encircling the planet. The global wind belts are enormous and the winds are relatively steady (Figure below). These winds are the result of air move at the bottom of the major atmospheric circulation cells, where the air moves horizontally from high to depression pressure.

The major wind belts and the directions that they blow.

Global Wind Belts

Permit'due south look at the global wind belts in the Northern Hemisphere.

In the Hadley prison cell air should move northward to s, but it is deflected to the right by Coriolis. And so the air blows from northeast to the southwest. This belt is the trade winds, then called considering at the time of sailing ships they were good for trade.
In the Ferrel cell air should move south to n, only the winds actually blow from the southwest. This belt is the westerly winds or westerlies. Why do y'all retrieve a flight beyond the U.s. from San Francisco to New York City takes less time than the contrary trip?
In the Polar prison cell, the winds travel from the northeast and are called the polar easterlies

The current of air belts are named for the directions from which the winds come. The westerly winds, for instance, accident from westward to east. These names hold for the winds in the current of air belts of the Southern Hemisphere likewise.

This video lecture discusses the iii-prison cell model of atmospheric circulation and the resulting global wind belts and surface wind currents (5a): http://www.youtube.com/sentry?five=HWFDKdxK75E (8:45).

Global Winds and Atmospheric precipitation

Besides their effect on the global wind belts, the high and low pressure areas created past the six atmospheric circulation cells make up one's mind in a general way the corporeality of precipitation a region receives. In low pressure regions, where air is ascension, rain is mutual. In high pressure areas, the sinking air causes evaporation and the region is ordinarily dry. More specific climate effects volition be described in the affiliate about climate.

Polar Fronts and Jet Streams

The polar front is the junction betwixt the Ferrell and Polar cells. At this low pressure zone, relatively warm, moist air of the Ferrell Cell runs into relatively cold, dry air of the Polar cell. The atmospheric condition where these two meet is extremely variable, typical of much of N America and Europe.

The polar jet stream is constitute high upwards in the atmosphere where the ii cells come together. A jet stream is a fast-flowing river of air at the boundary between the troposphere and the stratosphere. Jet streams grade where there is a large temperature departure betwixt ii air masses. This explains why the polar jet stream is the earth's most powerful (Figure beneath).

A cantankerous section of the atmosphere with major circulation cells and jet streams. The polar jet stream is the site of extremely turbulent weather condition.

Jet streams move seasonally just as the angle of the Sun in the heaven moves north and south. The polar jet stream, known every bit "the jet stream," moves south in the winter and north in the summer between almost thirty°Due north and 50° to 75°N.

Lesson Summary

Winds blow from high force per unit area zones to depression force per unit area zones. The pressure zones are created when air near the basis becomes warmer or colder than the air nearby.
Local winds may be plant in a mount valley or near a coast.
The global wind patterns are long-term, steady winds that prevail around a large portion of the planet.
The location of the global wind belts has a great deal of influence on the weather and climate of an area.

Review Questions

Draw a picture of a convection cell in the atmosphere. Label the depression and loftier pressure zones and where the wind is.
Nether what circumstances will winds exist very strong?
Given what you know about global-scale convection cells, where would y'all travel if you were interested in experiencing warm, plentiful rain?
Depict the atmospheric circulation for 2 places where you are likely to find deserts, and explain why these regions are relatively warm and dry out.
How could the Indian monsoons exist reduced in magnitude? What issue would a reduction in these of import monsoons have on that role of the world?
Why is the name "snow eater" an apt description of Chinook winds?
Why does the Coriolis Event cause air to appear to motion clockwise in the Northern Hemisphere? When does Coriolis Result cause air to appear to move counterclockwise?
Sailors once referred to a portion of the ocean equally the doldrums. This is a region where at that place is oft no wind, so ships would become becalmed for days or even weeks. Where do you call up the doldrums might be relative to the atmospheric apportionment cells?
Imagine that the jet stream is located farther south than usual for the summer. What is the weather similar in regions just north of the jet stream, equally compared to a normal summertime?
Give a general description of how winds form.

Points to Consider

How do local winds affect the weather condition in an area?
How do the global wind belts affect the climate in an area?
What are the primary principles that control how the atmosphere circulates?

Source: https://courses.lumenlearning.com/sanjac-earthscience/chapter/air-movement/

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