Earth Science Winds & air masses

1. WindsWinds

2. Wind is theWind is the horizontalhorizontal movement of air frommovement of air from
an area ofan area of highhigh pressure to an area ofpressure to an area of lowlow
pressure.pressure. All winds are causedAll winds are caused
by differences inby differences in airair
pressurepressure
 Most differences in airMost differences in air
pressure are due topressure are due to
unequalunequal heatingheating in thein the
atmosphereatmosphere
 Water has a higherWater has a higher
specific heatspecific heat thanthan
sand, so it heats muchsand, so it heats much
slower.slower.
 CoolCool, dense air sinks, dense air sinks
and has higher airand has higher air
pressurepressure
 WarmWarm, less dense air, less dense air
rises and has lowerrises and has lower
pressurepressure

3. Why Air Moves
 Air Rises at the Equator
and Sinks at the Poles
As the cold air sinks, it
creates areas of high
pressure around the
poles. This cold polar air
then flows toward the
equator.
 Pressure Belts Are
Found Every 30º
Convection cells are
separated by pressure
belts, bands of high and
low pressure.

4. Global WindsGlobal Winds
 Caused by globalCaused by global
convection currentsconvection currents..
 They blow steadily fromThey blow steadily from
specific directions overspecific directions over
great distances.great distances.
 The high pressure coolThe high pressure cool
air at the poles tries to fillair at the poles tries to fill
in the low pressure areasin the low pressure areas
at the equator.at the equator.
 This causes theThis causes the globalglobal
winds.winds.
 This is why the weatherThis is why the weather
systems tend to alwayssystems tend to always
come from west to east income from west to east in
Georgia.Georgia.

5. Polar EasterliesPolar Easterlies
 Wind belts thatWind belts that
extend from theextend from the
poles topoles to 6060°°
latitudelatitude
 Formed from coldFormed from cold
sinking air movingsinking air moving
from the polesfrom the poles
creatingcreating coldcold
temperaturestemperatures

6. WesterliesWesterlies
Wind belts foundWind belts found
between 30between 30°°
and 60° latitudeand 60° latitude
Flow towardsFlow towards
the poles fromthe poles from
west to eastwest to east
carryingcarrying moistmoist
airair over theover the
United StatesUnited States

7. Trade WindsTrade Winds
Winds that blowWinds that blow
fromfrom 3030° almost° almost
to the equatorto the equator
Called the tradeCalled the trade
winds because ofwinds because of
their use bytheir use by earlyearly
sailorssailors

8. Doldrums and Horse LatitudesDoldrums and Horse Latitudes
DoldrumsDoldrums
 Located along theLocated along the
equator whereequator where nono
winds blowwinds blow
because the warmbecause the warm
rising air createsrising air creates
and area of lowand area of low
pressurepressure
Horse LatitudesHorse Latitudes
 Occur at about 30Occur at about 30° north° north
and south of the equatorand south of the equator
where the winds arewhere the winds are
very weakvery weak
 Most deserts on theMost deserts on the
Earth are located hereEarth are located here
because of thebecause of the dry airdry air

10. Jet StreamJet Stream
 The jet streams areThe jet streams are
narrow belts ofnarrow belts of
high speedhigh speed windswinds
that blow in thethat blow in the
upperupper tropospheretroposphere
and lowerand lower
stratospherestratosphere
 SeparatesSeparates warmwarm
air from cold airair from cold air

12. Pressure CellsPressure Cells
 The earth isThe earth is
encircled byencircled by
several broadseveral broad
prevailing windprevailing wind
belts.belts.
 The threeThe three
primaryprimary
circulation cellscirculation cells
are known asare known as
the:the: HadleyHadley cell;cell;
FerrelFerrel cell; andcell; and
PolarPolar cell.cell.

13. Why Air Moves, continued
• The Coriolis Effect
The apparent
curving of the path
of currents due to
the Earth’s rotation
is called the Coriolis
effect.
• This causes winds
to curve to the right
in the northern
hemisphere, and the
opposite in the
southern
hemisphere.

15. Measuring WindsMeasuring Winds
 Winds are described byWinds are described by
theirtheir directiondirection and speedand speed
 A windA wind vanevane determinesdetermines
wind directionwind direction
 The name of a wind is theThe name of a wind is the
direction it is coming fromdirection it is coming from
so a north wind is fromso a north wind is from
thethe northnorth. It is headed to. It is headed to
thethe southsouth..
 Wind speed is measuredWind speed is measured
with anwith an anemometeranemometer..

16. Local winds are. . .Local winds are. . .
 Winds that blow overWinds that blow over
shortshort distancesdistances
 Caused byCaused by unequalunequal
heating of the earth’sheating of the earth’s
surface within a smallsurface within a small
areaarea
 This creates localThis creates local
convection currents.convection currents.
 Form only when no windsForm only when no winds
are blowing from far awayare blowing from far away

17. Sea BreezeSea Breeze
 In the morning the sandIn the morning the sand
heats up much faster thanheats up much faster than
the water, so the airthe water, so the air
above the sand is hotter.above the sand is hotter.
 Hotter air is less dense, soHotter air is less dense, so
it rises.it rises.
 The cooler air over theThe cooler air over the
ocean will push in to causeocean will push in to cause
the hot air to rise.the hot air to rise.
 So in the morning the windSo in the morning the wind
is in your face as you faceis in your face as you face
the ocean.the ocean.

18. Sea Breeze 2Sea Breeze 2
 1. Warm air1. Warm air
over land risesover land rises
 2. Sea Breeze2. Sea Breeze
moves inlandmoves inland
 3. Cumuli3. Cumuli
develop aloftdevelop aloft
and moveand move
seawardseaward
 4. Upper level4. Upper level
return landreturn land
breezebreeze
 5. Cool air5. Cool air
aloft sinks overaloft sinks over
waterwater
 6. Sea Breeze6. Sea Breeze

19. Land BreezeLand Breeze
 At night, the sand coolsAt night, the sand cools
very quickly, while thevery quickly, while the
ocean temperature changesocean temperature changes
very little.very little.
 So the warm air over theSo the warm air over the
ocean rises, pushed up byocean rises, pushed up by
the cooler air over thethe cooler air over the
beach.beach.
 So the wind will hit yourSo the wind will hit your
back as you look out overback as you look out over
the ocean at night.the ocean at night.

20. Land Breeze 2Land Breeze 2
 1. Cool air over1. Cool air over
land sinksland sinks
 2. Land Breeze2. Land Breeze
moves out overmoves out over
waterwater
 3. Relatively3. Relatively
warmer waterwarmer water
heats air whichheats air which
then risesthen rises
 4. Upper level4. Upper level
return sea breezereturn sea breeze
 5. Cool air over5. Cool air over
land sinksland sinks

21. Sea/Land BreezesSea/Land Breezes