what is the movement of hot air up to cooler air

Lesson Objectives

List the properties of the air currents within a convection jail cell.
Describe how high and low pressure cells create local winds and explicate how several types of local winds form.
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 breeze
low pressure zone
monsoon
mountain breeze
polar front
rainshadow effect
Santa Ana winds
ocean cakewalk
valley breeze

Introduction

A few basic principles become a long way toward explaining how and why air moves: Warm air rising creates a low pressure zone at the ground. Air from the surrounding area is sucked into the infinite left by the rising air. Air flows horizontally at top of the troposphere; horizontal flow is chosen advection. The air cools until it descends. Where it reaches the ground, it creates a high pressure level zone. Air flowing from areas of loftier pressure to low pressure level creates winds. Warm air tin can hold more moisture than cold air. Air moving at the bases of the iii major convection cells in each hemisphere north and south of the equator creates the global wind belts.

Air Pressure and Winds

Inside the troposphere are convection cells (Effigy below).

Warm air rises, creating a low force per unit area zone; cool air sinks, creating a high pressure zone.

Air that moves horizontally between high and low pressure zones makes air current. The greater the pressure difference between the pressure zones the faster the wind moves.

Convection in the temper creates the planet's weather. When warm air rises and cools in a low pressure zone, it may not exist able to hold all the water information technology contains as vapor. Some water vapor may condense to class clouds or precipitation. When cool air descends, it warms. Since information technology tin then concur more moisture, the descending air will evaporate h2o on the ground.

Air moving betwixt large loftier and low pressure systems creates the global wind belts that profoundly touch regional climate. Smaller force per unit area systems create localized winds that touch on the weather and climate of a local expanse.

An online guide to air pressure and winds from the Academy of Illinois is found here: http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/home.rxml.

Local Winds

Local winds result from air moving between small low and high pressure systems. High and low force per unit area cells are created past a multifariousness of conditions. Some local winds have very important furnishings on the atmospheric condition and climate of some regions.

Land and Sea Breezes

Since water has a very high specific estrus, it maintains its temperature well. So h2o heats and cools more slowly than state. If there is a large temperature divergence between the surface of the sea (or a large lake) and the land next to it, high and low force per unit area regions form. This creates local winds.

Bounding main breezes blow from the libation ocean over the warmer country in summer (Figure beneath). Where is the loftier pressure level zone and where is the depression pressure zone? Sea breezes accident at well-nigh 10 to twenty km (six 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 high pressure zone and where is the low force per unit area zone? Some warmer air from the bounding main rises and and then sinks on land, causing the temperature over the land to become warmer.

How do sea and land breezes moderate coastal climates?

Country and body of water breezes create the pleasant climate for which Southern California is known. The effect of land and body of water breezes are felt only about 50 to 100 km (xxx to 60 miles) inland. This same cooling and warming effect occurs to a smaller degree during solar day and night, because land warms and cools faster than the ocean.

Monsoon Winds

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

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

The nigh important monsoon in the globe occurs each yr over the Indian subcontinent. More than ii billion residents of Republic of india and southeastern Asia depend on monsoon rains for their drinking and irrigation water. Back in the days of sailing ships, seasonal shifts in the monsoon winds carried goods back and forth betwixt India and Africa.

Mountain and Valley Breezes

Temperature differences betwixt mountains and valleys create mount and valley breezes. During the day, air on mount slopes is heated more than than air at the same height over an adjacent valley. As the day progresses, warm air rises and draws the absurd air up from the valley, creating a valley cakewalk. At night the mountain slopes cool more chop-chop than the nearby valley, which causes a mountain breeze to catamenia downhill.

Katabatic Winds

Katabatic winds move upwards and downwardly slopes, but they are stronger mount and valley breezes. Katabatic winds form over a loftier land area, similar a high plateau. The plateau is normally surrounded on almost all sides past mountains. In winter, the plateau grows common cold. The air above the plateau grows common cold and sinks downwards from the plateau through gaps in the mountains. Current of air speeds depend on the divergence in air pressure over the plateau and over the surroundings. Katabatic winds course 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 upward 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, information technology cools and contracts. If the air is boiling, information technology may class clouds and drop rain or snow. When the air sinks on the leeward side of the mountains, it forms a high pressure level zone. The windward side of a mountain range is the side that receives the current of air; the leeward side is the side where air sinks.

The descending air warms and creates strong, dry out winds. Chinook winds can heighten temperatures more than xx°C (36°F) in an 60 minutes and they rapidly decrease humidity. Snow on the leeward side of the mount disappears melts quickly. If precipitation falls equally the air rises over the mountains, the air will be dry as information technology sinks on the leeward size. This dry, sinking air causes a rainshadow effect (Figure below), which creates many of the world'southward deserts.

As air rises over a mount it 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 consequence.

Santa Ana Winds

Santa Ana winds are created in the belatedly fall and winter when the Great Basin east of the Sierra Nevada cools, creating a high force per unit area zone. The high pressure forces winds downhill and in a clockwise direction (considering of Coriolis). The air pressure rises, so temperature rises and humidity falls. The winds blow beyond the Southwestern deserts then race downhill and west toward the ocean. Air is forced through canyons cutting the San Gabriel and San Bernardino mountains (Figure below).

The winds are specially fast through Santa Ana Coulee, for which they are named. Santa Ana winds blow dust and fume westward over the Pacific from Southern California.

The Santa Ana winds often arrive at the end of California'due south long summer drought season. The hot, dry winds dry out the landscape even more. If a fire starts, it can spread quickly, causing large-scale devastation (Effigy below).

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

Desert Winds

High summertime temperatures on the desert create loftier winds, which are often associated with monsoon storms. Desert winds pick up grit because in that location is not as much vegetation to hold down the clay and sand. (Effigy below). A haboob forms in the downdrafts on the front of a thunderstorm.

A haboob in the Phoenix metropolitan area, Arizona.

Dust devils, also called whirlwinds, course as the ground becomes so hot that the air above it heats and rises. Air flows into the low pressure and begins to spin. Dust devils are small and short-lived but they may crusade damage.

Atmospheric Circulation

Considering more solar energy hits the equator, the air warms and forms a depression pressure zone. At the summit of the troposphere, half moves toward the North Pole and half toward the Southward Pole. As it moves along the pinnacle of the troposphere information technology cools. The cool air is dense and when it reaches a high force per unit area zone it sinks to the ground. The air is sucked back toward the low pressure at the equator. This describes the convection cells north and south of the equator.

If the Earth did not rotate, there would be one convection jail 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 Effect must exist taken into business relationship. Coriolis Consequence was described in the Earth's Oceans chapter.

Let's look at atmospheric circulation in the Northern Hemisphere as a result of the Coriolis Issue (Figure below). Air rises at the equator, but equally it moves toward the pole at the summit of the troposphere, it deflects to the correct. (Call up that it just appears to deflect to the right because the ground below it moves.) At about thirty°N latitude, the air from the equator meets air flowing toward the equator from the college latitudes. This air is cool because information technology has come up from higher latitudes. Both batches of air descend, creating a loftier pressure zone. In one case on the ground, the air returns to the equator. This convection cell is chosen the Hadley Cell and is found between 0° and 30°N.

The atmospheric apportionment cells, showing direction of winds at Globe's surface.

In that location are two more convection cells in the Northern Hemisphere. The Ferrell prison cell is between thirty°N and fifty° to 60°N. This prison cell shares its southern, descending side with the Hadley cell to its s. Its northern ascension limb is shared with the Polar prison cell located between l°Northward to lx°Due north and the North Pole, where cold air descends.

At that place are three mirror image circulation cells in the Southern Hemisphere. In that hemisphere, the Coriolis Event makes objects announced 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 movement at the bottom of the major atmospheric circulation cells, where the air moves horizontally from loftier to low pressure.

The major wind belts and the directions that they blow.

Global Wind Belts

Allow's wait at the global air current belts in the Northern Hemisphere.

In the Hadley cell air should movement north to due south, but it is deflected to the right by Coriolis. And then the air blows from northeast to the southwest. This belt is the trade winds, and so called because at the fourth dimension of sailing ships they were practiced for trade.
In the Ferrel jail cell air should move south to n, just the winds actually blow from the southwest. This chugalug is the westerly winds or westerlies. Why exercise you think a flight across the United states from San Francisco to New York Metropolis takes less time than the reverse trip?
In the Polar cell, the winds travel from the northeast and are called the polar easterlies

The wind belts are named for the directions from which the winds come. The westerly winds, for example, accident from westward to east. These names hold for the winds in the wind belts of the Southern Hemisphere as well.

This video lecture discusses the 3-jail cell model of atmospheric circulation and the resulting global wind belts and surface wind currents (5a): http://www.youtube.com/watch?v=HWFDKdxK75E (viii:45).

Global Winds and Atmospheric precipitation

Besides their issue on the global air current belts, the high and low pressure areas created by the half dozen atmospheric circulation cells decide in a full general way the amount of precipitation a region receives. In low pressure regions, where air is rising, pelting is common. In loftier pressure areas, the sinking air causes evaporation and the region is ordinarily dry. More specific climate effects volition be described in the chapter about climate.

Polar Fronts and Jet Streams

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

The polar jet stream is constitute high upward in the atmosphere where the two cells come together. A jet stream is a fast-flowing river of air at the boundary betwixt the troposphere and the stratosphere. Jet streams form where there is a big temperature difference betwixt two air masses. This explains why the polar jet stream is the globe'south about powerful (Figure below).

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

Jet streams motion seasonally only as the angle of the Sun in the heaven moves due north and southward. The polar jet stream, known every bit "the jet stream," moves due south in the winter and north in the summer between about thirty°N and 50° to 75°N.

Lesson Summary

Winds blow from high pressure zones to low pressure zones. The pressure zones are created when air most the ground becomes warmer or colder than the air nearby.
Local winds may be found in a mountain valley or near a coast.
The global air current patterns are long-term, steady winds that prevail effectually a large portion of the planet.
The location of the global wind belts has a nifty deal of influence on the weather and climate of an expanse.

Review Questions

Depict a picture show of a convection cell in the atmosphere. Characterization the low and high force per unit area zones and where the wind is.
Under what circumstances volition winds be 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?
Describe the atmospheric circulation for two places where you are likely to find deserts, and explain why these regions are relatively warm and dry out.
How could the Indian monsoons be reduced in magnitude? What effect would a reduction in these of import monsoons have on that office of the world?
Why is the proper name "snow eater" an apt clarification of Chinook winds?
Why does the Coriolis Event crusade air to announced to move clockwise in the Northern Hemisphere? When does Coriolis Effect cause air to announced to movement counterclockwise?
Sailors once referred to a portion of the ocean as the doldrums. This is a region where at that place is oftentimes no wind, and then ships would become becalmed for days or even weeks. Where practice you remember the doldrums might exist relative to the atmospheric circulation cells?
Imagine that the jet stream is located further s than usual for the summertime. What is the weather condition like in regions just due north of the jet stream, as compared to a normal summer?
Give a general description of how winds grade.

Points to Consider

How do local winds bear upon the weather in an area?
How exercise the global wind belts affect the climate in an area?
What are the main principles that command how the atmosphere circulates?

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