View
219
Download
0
Category
Preview:
Citation preview
7/25/2019 -Circulation in the Atmosphere
1/53
Solar Radiation - initial source of energy to theEarth. It can be absorbed, reflected andreradiated. The redistribution of this energycontrols the structure and dynamics of theAtmosphere and Oceans.
Circulation of the Atmosphere
7/25/2019 -Circulation in the Atmosphere
2/53
The Atmosphere Is Composed Mainly ofNitrogen, Oxygen, and Water Vapor
What are some properties of the atmosphere?
The lower atmosphere is a fairly homogeneous mixture of gases.Water vapor occupies up to 4% of the volume of the atmosphere.The density of air is influenced by temperature and water content.
Ascending air cools as it expands. Cooler
air can hold less water, so water vaporcondenses into tiny droplets - clouds.Descending air warms as it compresses the droplets (clouds) evaporate.
7/25/2019 -Circulation in the Atmosphere
3/53
GreenhouseGases
Gases: permanent andvariable
Permanent =present inconstant relative% of total volume Variable =
concentrationchanges with timeand location
Suspendedmicroscopic particles
Water droplets
7/25/2019 -Circulation in the Atmosphere
4/53
The Atmosphere Moves in Response to UnevenSolar Heating and Earths Rotation
An estimate of the heat budget for Earth. On an average day, about half ofthe solar energy arriving at the upper atmosphere is absorbed at Earthssurface. Light (short-wave) energy absorbed at the surface is converted intoheat. Heat leaves Earth as infrared (long-wave) radiation. Since input equals
output over long periods of time, the heat budget is balanced.
7/25/2019 -Circulation in the Atmosphere
5/53
7/25/2019 -Circulation in the Atmosphere
6/53
Heat budget
Solar input must balance solar output
Temperature increases/decreases if input isgreater/less than output
Average Earth Temperature is 16
o
C Solar Energy is reradiated from the surface as a longwave.
Surface of Earth (including oceans) is heated from
above Atmosphere is heated from below
7/25/2019 -Circulation in the Atmosphere
7/53
O3absorbsUV Solar
Radiation,heatsAtm.
Vertical (thermal) structure of theatmosphere
Troposphere: lowest layer 0-12 km,temperature decreases with altitude Tropopause: minimum temperaturezone between the troposphere andstratosphere Stratosphere: layer above
tropopause 12-50 km, temperatureincreases with altitude Mesosphere: layer abovestratosphere 50-90 km, temperaturedecreases with height Thermosphere: layer above
mesosphere >90 km, extends out tospace
The Atmosphere
Density of air depends on temperature, water vapor and altitudeTemperature decrease = density increase
Water vapor increase = density decreaseAltitude increase = density decrease
7/25/2019 -Circulation in the Atmosphere
8/53
The Solar Heating of Earth Varies withLatitude
How solar energy input varies
with latitude.
Equal amounts of sunlight arespread over a greater surfacearea near the poles than in thetropics.
Ice near the poles reflectsmuch of the energy thatreaches the surface there.
The atmosphere reflects, scatters and absorbs solar radiation. At highlatitudes solar radiation travels a longer path through atmosphere.
7/25/2019 -Circulation in the Atmosphere
9/53
The Solar Heating of Earth Varies with Latitude
Earth as a whole is in thermal
equilibrium, but different latitudes arenot.
The average annual incoming solar radiation(red line) absorbed by Earth and the averageannual infrared radiation (blue line) emittedby Earth. Polar latitudes lose more heat to
space than they gain, and tropical latitudesgain more heat than they lose. The amount ofradiation received equal the amount lost atabout 38N and S. The area of heat gained(orange area) equals the area of heat lost(blue areas) so Earths total heat budget isbalanced.
What factors govern the global circulation of air?
Uneven solar heating
The Coriolis effect
7/25/2019 -Circulation in the Atmosphere
10/53
Warm equatorial water flows to higher latitudes
Cool Polar water flow to lower latitudes
Re-distribution of heat
Heat gained at Equatorial latitudes
Heat lost at higher latitudes Winds and ocean currents redistribute heat around
the EarthOceans do not boil away near the equator or freeze solid near
the poles because heat is transferred by winds and oceancurrents from equatorial to polar regions.
7/25/2019 -Circulation in the Atmosphere
11/53
The Seasons: solar heating varies with seasons
During the Northern Hemisphere winter, the Southern Hemisphere istilted toward the sun and the Northern Hemisphere receives less light and
heat. During the Northern Hemisphere summer, the situation is reversed.
* Earth revolves around theSun (365 days)
* Earth rotates about its ownaxis (1 day)
* angle (tilt) that axis ofrotation makes with planethat contains trajectoryaround the Sun is 23 andit remains that way (sameorientation) as the Earth
revolves around Sun
7/25/2019 -Circulation in the Atmosphere
12/53
Winter (Northern Hemisphere
tilts away from sun)Spring (sun aims
directly at
equator)
Summer
(Northern
Hemisphere tilts
toward sun) Fall(sun aims
directly at
equator)
To
Polaris
The tilt (23 inclination) causes the seasons
7/25/2019 -Circulation in the Atmosphere
13/53
Earths Uneven Solar Heating Results in Large-Scale Thermal Cell type of Atmospheric Circulation
A convection current formsin a room when air flowsfrom a hot radiator to a coldwindow and back.
Air warms, expands,becomes less dense, andrises over the radiator. Aircools, contracts, becomesmore dense, and falls nearthe cold glass window.
A convection cell is driven by density differences
7/25/2019 -Circulation in the Atmosphere
14/53
7/25/2019 -Circulation in the Atmosphere
15/53
The Coriolis Effect Deflects the Path ofMoving Objects
Sketch of the thought experiment in thetext, showing that Buffalo travels ashorter path on the rotating Earth eachday then Quito does.
A continuation of the thought experiment.A look at Earth from above the North Poleshows that Buffalo and Quito move atdifferent velocities.
7/25/2019 -Circulation in the Atmosphere
16/53
The Coriolis Effect Deflects the Pathof Moving Objects
As observed from space,cannonball 1 (shot northward)and cannonball 2 (shotsouthward) move as we mightexpect; that is, they travelstraight away from the cannonsand fall to Earth.
Observed from the ground,however, cannonball 1 veersslightly east and cannonball 2veers slightly west of their
intended targets.The effect depends on theobservers frame of reference.
7/25/2019 -Circulation in the Atmosphere
17/53
The Coriolis Effect Influences the Movement ofAir in Atmospheric Circulation Cells
Global air circulation as described in the six-cell circulation model. Air rises atthe equator and falls at the poles, but instead of one great circuit in eachhemisphere from equator to pole, there are three in each hemisphere. Note the
influence of the Coriolis effect on wind direction. The circulation show here isidea that is, a long-term average of wind flow.
7/25/2019 -Circulation in the Atmosphere
18/53
Wind bands Three convectioncells in each hemisphere
Trade winds = NE (30N to
0) and SE (30S to 0)Westerlies = 60N to30N and 60S to 30S
Polar easterlies = 90Nto 60N and 90S to
60SLow pressure at 0, 60N,and 60S
Low pressure, ascending air,clouds, increased
precipitationHigh pressure at 30N, 30S,90N, and 90SHigh pressure, descendingair, clear skies, low
precipitation
7/25/2019 -Circulation in the Atmosphere
19/53
The Coriolis Effect Influences the Movement ofAir in Atmospheric Circulation Cells
A large circuit of air is called an atmospheric circulation cell.
Three cells exist in each hemisphere.
Hadley cells are tropical cells found on each side of the equator.
Ferrel cells are found at the mid-latitudes.Polar cells are found near the poles.
What are some of the wind patterns found between and withincells?
Doldrums are calm equatorial areas where two Hadley cells
convergeHorse latitudes are areas between Hadley and Ferrel cells.Trade winds are surface winds of Hadley cells.Westerlies are surface winds of Ferrel cells.
7/25/2019 -Circulation in the Atmosphere
20/53
20
THE THREE CELL MODEL
FORMATION OF THE HADLEY CELL (1)
SOLAR ENERGY
Insolation in tropicalareas causes warm airto rise and spreadpolewards, carryingheat energy.
7/25/2019 -Circulation in the Atmosphere
21/53
21
THE THREE CELL MODEL
FORMATION OF THE HADLEY CELL (2)
SOLAR ENERGY
Air cools and begins to fall at
about 30N and 30S of Equator.Cooled air returns to the Equator.
This circulation of air iscaused by solar heating.
It is called the HADLEY CELL.
Heat energy is transferredfrom the Equator to sub-
tropical latitudes.
7/25/2019 -Circulation in the Atmosphere
22/53
22
THE THREE CELL MODEL
FORMATION OF THE POLAR CELL (1)
Intensely cold,
dense air sinks atthe poles, thenblows as surfacewinds towards theEquator.
7/25/2019 -Circulation in the Atmosphere
23/53
23
THE THREE CELL MODEL
FORMATION OF THE POLAR CELL (2)
This circular motion iscalled the POLAR CELL.
At about 60N and 60 S,the cold polar air is warmedin contact with the earthssurface.
This warmed air rises andreturns polewards,carrying heat energy.
7/25/2019 -Circulation in the Atmosphere
24/53
24
THE THREE CELL MODEL
FORMATION OF THE FERREL CELL (1)
The Hadley Cell is drivenby differences in heatenergy at the Equator.
As the air in the HadleyCell falls at about 30Nand 30S, it pulls the airbeside it down as well,due to friction
THE THREE CELL MODEL
7/25/2019 -Circulation in the Atmosphere
25/53
25
THE THREE CELL MODEL
FORMATION OF THE FERREL CELL (2)
The Polar Cell is driven by
differences in heat energy.Cold polar air falls andspreads towards the Equator.
As the air in the Polar Cellrises at about 60N and60S, it pulls the air
beside it up as well, due tofriction.
7/25/2019 -Circulation in the Atmosphere
26/53
26
THE THREE CELL MODEL
FORMATION OF THE FERREL CELL (3)
The Polar Cell causes anuplift at about 60N andS.
Unlike the Hadley and PolarCells, the Ferrel Cell is not
driven by differences in heatenergy.
The Ferrel Cell is caused byfriction where air is incontact with the other twocells.
The Hadley Cell drags airdown at about 30N and S.
7/25/2019 -Circulation in the Atmosphere
27/53
27
THE THREE CELLS TOGETHER
Ferrel Cell
Polar Cell
Hadley Cell
Polar Cell
Ferrel Cell
Hadley Cell
7/25/2019 -Circulation in the Atmosphere
28/53
28
THE TRANSFER OF HEAT ENERGY FROM
EQUATORIAL TO POLAR AREAS
Where air carrying energy from theEquator in the Hadley Cell comes into
contact with air in the Ferrel Cell,there is a transfer of heat energyinto the Ferrel Cell.
There is a similar transferof heat energy from the
Ferrel Cell to the Polar Cell.
In this way, heat energy istransferred from the Equator,where there is a surplus ofenergy, to the poles wherethere is a deficit.
SOLAR ENERGY
7/25/2019 -Circulation in the Atmosphere
29/53
29
THE CORRESPONDING MOVEMENT OF COLDER AIR
In the Polar cell cold air from polarregions flows to mid-latitudes as
polar easterly winds
In the Ferrel Cell there is amovement of cold air athigh altitude.
In the Hadley Cell, coolerair moves from the sub-tropics to the Equator.
7/25/2019 -Circulation in the Atmosphere
30/53
30
ASSOCIATED PRESSURE BELTS
Rising air at the equator causes theequatorial belt of low pressure
Descending air at about 30N and30S causes the sub-tropical beltof high pressure
Rising air at about 60N and60S causes a mid-latitudebelt of low pressure
Descending air at the polescauses the polar highpressure areas
Mid latitude low pressure
Mid latitude low pressure
Equatorial low pressure
Sub-tropical high pressure
Sub-tropical high pressure
Polar high pressure
Polar high pressure
7/25/2019 -Circulation in the Atmosphere
31/53
31
ASSOCIATED SURFACE WIND PATTERNS
Winds always blow from high pressure to
low pressure.They are deflected because of theCoriolis Force which come about becauseof the rotation of the earth.
Winds in Northern Hemisphereare deflected to the right.
Winds in the southern hemisphereare deflected to the left.
These wind belts shiftseasonally. (See next section) Mid latitude low pressure
Equatorial low pressure
Sub-tropical high pressure
Polar high pressure
Mid latitude low pressure
Sub-tropical high pressure
Polar high pressure
7/25/2019 -Circulation in the Atmosphere
32/53
32
7/25/2019 -Circulation in the Atmosphere
33/53
33
POSITION OF THE THREE CELLS IN DECEMBER
Polar Cell
Hadley
Cell
FerrelCell
Polar Cell
FerrelCell
Hadley
Cell
SUN OVERHEAD 23S
The sun is overhead at theTropic of Capricorn, 23Sof the Equator.
The cells shiftsouthwards as the
heat equator is in thesouthern hemisphere.
7/25/2019 -Circulation in the Atmosphere
34/53
7/25/2019 -Circulation in the Atmosphere
35/53
35
Equatorial low pressure
Sub-tropical high pressure
Sub-tropical high pressure
IN THE NORTHERN HEMISPHERE:
The winds that blow to the equatoriallow pressure belt are called the NorthEast Trade Winds
The line along which they converge
(meet) is called the INTER-TROPICAL CONVERGENCE ZONE.
This is often abbreviated to ITCZ
THE INTER-TROPICAL CONVERGENCE ZONE
IN THE SOUTHERN HEMISPHERE:
The winds that blow to theequatorial low pressure belt arecalled the South East Trade Winds
Inter-Tropical Convergence Zone
7/25/2019 -Circulation in the Atmosphere
36/53
36
Equatorial low pressure
Sub-tropical high pressure
Sub-tropical high pressure
IN THE NORTHERN HEMISPHERE
OVER WEST AFRICA
The sub-tropical high pressure beltdevelops over the Sahara so is hot anddry.
This is known as continental Tropical(cT) air.
THE INTER-TROPICAL CONVERGENCE ZONE
Inter-Tropical Convergence ZoneIN THE SOUTHERN HEMISPHERE
OVER WEST AFRICA
The sub-tropical high pressure belt
develops over the Atlantic so is warmand moist.
This is known at maritime Tropical (mT)air.
7/25/2019 -Circulation in the Atmosphere
37/53
37
In December, the zone of maximuminsolation (solar energy) is south ofthe Equator. This means that the wind
belts shift southwards.
This means that winds blow out of thesub-tropical high pressure area over theSahara, and take dry air from thecontinental Tropical (cT) air mass acrossmost of West Africa. This causes a dryseason.
THE ITCZ IN DECEMBER
SOLAR ENERGY
Moist air from the maritimeTropical(mT) air mass from the Atlantic cannotreach far inland, where there is a dryseason.
7/25/2019 -Circulation in the Atmosphere
38/53
38
THE ITCZ IN JUNE
By contrast, in June, the zone ofmaximum insolation is well to the north
of the Equator. This means that thewind belts shift northwards.
The winds blow out of the sub-tropical highpressure area over the Sahara, now only affect
the northern part of sub-Saharan Africa.
SOLAR ENERGY
Moist maritime Tropical air from theAtlantic now reaches far inland, wherethere is a rainy season. These winds flow
northwards to the ITCZ to replace airthat has become unstable and risen.
7/25/2019 -Circulation in the Atmosphere
39/53
Monsoons Are Wind Patterns That Change withthe Seasons
Monsoons are patterns of wind circulation that change with the season.Areas with monsoons generally have dry winters and wet summers.
Sea breeze is cool air from over the water moving toward land. Seabreezes occur after sunrise.
Land breezes occur after sunset when air warmed by the land blowstoward the water.
7/25/2019 -Circulation in the Atmosphere
40/53
In the Northern Hemisphere
Air flows clockwise around high pressure systemsAir flows counterclockwise around low pressure systems
M A Wi d P tt Th t Ch
7/25/2019 -Circulation in the Atmosphere
41/53
Monsoons Are Wind Patterns That Changewith the Seasons
A monsoon is a pattern of windcirculation that changes with theseason. Locations where monsoons occurtypically have wet summers and drywinters.
Monsoon patterns.During the monsoon circulations ofJanuary (a) and July (b), surface windsare deflected to the right in theNorthern Hemisphere and to the left inthe Southern Hemisphere. (c) Detail ofsummer Asian monsoon, showing location
of Cherrapunji, India, one f the worldswettest places. Rainfall amounts therecan exceed 10 meters (425 inches) per
year!
Sea Breezes and Land
7/25/2019 -Circulation in the Atmosphere
42/53
Sea Breezes and LandBreezes Arise fromUneven Surface Heating
The flow of air in coastal regionsduring stable weather conditions.
(a) In the afternoon, the land iswarmer than the ocean surface,and the warm air rising from theland is replaced by an onshoresea breeze.
(b) At night, as the land cools,the air over the ocean is now
warmer than the air over theland. The ocean air rises. Airflows offshore to replace it,generating an offshore flow (aland breezes).
7/25/2019 -Circulation in the Atmosphere
43/53
Storms Are Variations in Large-ScaleAtmospheric Circulation
Storms are regional atmospheric disturbances. Storms have high windsand most have precipitation.
Tropical cyclones occur in tropical regions. These storms can causemillions of dollars worth of damage and endanger life.
Extratropical cyclones occur in Ferrel cells, and are winter weatherdisturbances. These storms can also cause extensive damage.
Both types of storms are cyclones, or rotating masses of low-pressureair.
7/25/2019 -Circulation in the Atmosphere
44/53
Extratropical Cyclones Form between Two AirMasses
(a) The genesis and earlydevelopment of anextratropical cyclone inthe Northern Hemisphere
(b) How precipitation
develops in anextratropical cyclone.These relationshipsbetween two contrastingair masses areresponsible for nearly allthe storms generated in
the polar frontal zone andthus responsible for thehigh rainfall within thesebelts and the decreasedsalinities of surfacewaters below.
7/25/2019 -Circulation in the Atmosphere
45/53
Tropical Cyclones Form in One Air Mass
The internal structure of a mature tropical cyclone, or hurricane.(The vertical dimension is exaggerated in this model of ahurricane.)
7/25/2019 -Circulation in the Atmosphere
46/53
Tropical Cyclones Form in One Air Mass
The dynamics of a tropical cyclone, showing the influence of the Corioliseffect. Note that the storm turns the wrong way (that is,counterclockwise) in the Northern Hemisphere, but for the right
reasons.
7/25/2019 -Circulation in the Atmosphere
47/53
Tropical Cyclones Form in One Air Mass
7/25/2019 -Circulation in the Atmosphere
48/53
Tropical Cyclones Form in One Air Mass
The tracks of tropical cyclones. The breeding grounds of tropical cyclones areshown as orange-shaded areas. The storms follow curving paths: First theymove westward with the trade winds. Then they either die over land or turneastward until they lose power over the cooler ocean of mid-latitudes. Cyclonesare not spawned over the South Atlantic or the southeast Pacific because theirwaters are too chilly; nor in the still air - the doldrums - within a few degrees
of the equator.
Hurricanes
7/25/2019 -Circulation in the Atmosphere
49/53
Hurricanes
Easterly waves = pressure disturbancesresulting from variations in trade winds due tochanging surface water temperature
Critical sea surface temperature = 27o C Decrease in atmospheric pressure
Increases evaporation rate Increased wind speeds
Energy from ocean fuels hurricanes
Water vapor extracted from warm seasurface
Energy released during condensation
7/25/2019 -Circulation in the Atmosphere
50/53
7/25/2019 -Circulation in the Atmosphere
51/53
Heat capacity (review)
Heat capacity of ocean is greater than that of land
Ocean currents, wind and waves can transfer heatdownward in summer and upward in winter
Larger seasonal variations of temperature over land Oceans control surface temperatures in Southern
Hemisphere
Land in the Northern Hemisphere influences the
range in surface temperature
Chapter 8 S mmar
7/25/2019 -Circulation in the Atmosphere
52/53
Chapter 8 - Summary
The interaction of ocean and atmosphere moderates surface
temperatures, shapes Earth's weather and climate, and creates most ofthe sea's waves and currents.
Different amounts of solar energy are absorbed at different latitudes,and this makes the tropics warmer than the polar regions.
Uneven solar heating causes convection currents to form in theatmosphere and leads to areas of different atmospheric pressures. Thedirection of air flow in these currents is influenced by the rotation ofEarth.
To observers on the surface, Earth's rotation causes moving air (or any
moving mass) in the Northern Hemisphere to curve to the rightof itsinitial path, and in the Southern Hemisphere to the left. This is known asthe Coriolis effect.
Chapter 8 Summary
7/25/2019 -Circulation in the Atmosphere
53/53
Chapter 8 - Summary
The atmosphere responds to uneven solar heating by flowing in three
great circulating cells over each hemisphere. The flow of air within thesecells is influenced by Earths rotation (Coriolis effect). Each hemispherehas three large atmospheric circulation cells: a Hadley cell, a Ferrel cell,and a polar cell (less pronounced over the South Pole).
Large storms are spinning areas of unstable air that develop between or
within air masses. Extratropical cyclones originate at the boundarybetween air masses.
Tropical cyclones, the most powerful of Earth's atmospheric storms,occur within a single humid air mass.
Recommended