Transcript Air Masses

*
*The relative measure of the amount of
water vapor in the air
*Psychrometer
*Water vapor affects the density of the
air.
*Cold air is heavier than warm air.
*
*A
body of air that has the same
temperature and humidity
throughout.
*
*If a large body of air sits over an area of
land or water for a long period of time,
it will take on the characteristics of the
land or water beneath it.
*Temperature
*Humidity
*
*Air masses over the equator will have high
temperatures.
*Air masses over polar regions will have low
temperatures.
*Air masses over water (maritime) will have high
humidity (moisture content).
*Air masses over land (continental) will have low
humidity (moisture content).
*
*Air masses tend to form in areas with
little wind.
*Remember, they sit over an area for a
long period of time without moving.
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*Air masses that form over water are
called maritime.
*Air masses that form over land are
called continental.
*
*mT – maritime tropical
*cT – continental tropical
*mP – maritime polar
*cP – continental polar
*cA – continental arctic
*
*
*mT – warm, moist air
*cT – warm, dry air
*mP – cold, moist air
*cP – cold, dry air
*cA – super cold, dry air
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Convection!
*
*Warm air rises, and cold air moves
in to replace it.
*A circulation pattern is formed.
*Causes air and water currents to
form
*
Density!
*Warm air rises.
*Cool air sinks.
*
How do different air masses
form?
*
*Hurricanes
*What is a hurricane?
* Hurricanes are tropical cyclones.
* They form in the southern Atlantic
Ocean,
Caribbean, Gulf of Mexico, and eastern Pacific
Ocean.
* Their winds spiral outward in a
counterclockwise, circulation pattern.
*What conditions must exist for a
hurricane to form?
* Low to medium winds blowing in the same direction
* 5–30 degrees north of the equator in the ocean
* Ocean surface temperature of greater than 80 F
that extends down to about 150 feet deep (50 m)
* Lower atmosphere must be moist
*How do hurricanes form?
* The air mass above the tropical waters takes on the
temperature and humidity of the water beneath it.
* Incoming winds force the air upward.
* The warm, moist air rises, forming water vapor and
clouds.
* Above the storm, the winds flow outward.
* Outside winds blow inward, and the cycle repeats.
*How do hurricanes move?
* Hurricanes turn to the right, away from the
equator, because of the Coriolis Effect caused
by Earth’s rotation.
* You will learn about this phenomenon later in
the lesson.
*Where does the energy for a
hurricane originate?
* The Sun heats the oceans.
* Warm air rises, and as it cools, it releases
energy, fueling the hurricane.
*Why don’t hurricanes form in
higher latitudes?
* The temperature of the oceans is not
warm enough.
* The distance is too far from the equator.
*Hurricane Katrina
*Reflective Question
How do oceans play a role in the development
of weather systems including hurricanes?
*Winds
*The movement of air in a
horizontal direction
*What is wind?
* The uneven heating of the Earth causes
differences in air pressure.
*What causes wind?
* The Sun’s energy is more concentrated at the Equator
and spread out more over the poles.
* Air over the equator is warm and less dense and has
lower pressure.
* Air over the poles is cold and denser and has higher
pressure.
*Why does this
happen?
* As warm air at the equator rises, cooler air
from the poles will move in and replace it.
* Air pressure moves in a pattern from high
to low.
*Why does this
happen?
*Convection
* As warm air at the equator rises, cooler
air from the poles will move in and
replace it.
* The density changes caused by temperature changes
create convection cells.
* These cause circular patterns of air that circulate over
the whole planet.
*Global
Convection
Currents
* Where the convections cells meet, prevailing winds and
jet streams form.
* They blow from one direction over a certain area of the
Earth’s surface.
*Global Wind Belts
*Jet Stream
*Jet Stream
* Forms high in the upper Troposphere between
two air masses of different temperatures
* Higher temperature difference = faster speed
* Due to the Coriolis Effect, it flows around air
masses.
* Polar Jet:
* It dips southward when frigid polar air masses move
south.
* It tends to stay north in the summer months.
http://www.pbs.org/wgbh/nova/vanished/jetstr_five.
html
*Jet Stream
Animation
*Prevailing Winds
* Named for the direction from which they
blow:
* Polar Easterlies – High latitudes blow east to west
toward the equator
* Westerlies – Mid latitudes blow west to east toward the
poles
* Easterlies (Trade Winds) – Low latitudes blow east to
west toward the Equator
*Prevailing Winds
*Prevailing Winds
* Pressure belts form in between the wind
belts.
MoreDirect
Sun Hot
90 o N
60 o N
30 o N
0 o Equator
30 o S
60 o S
90 o S
*Global Wind Belts
* The winds from the poles blow toward the equator.
* The winds from the equator blow toward the poles.
*
If wind is moving north and
south, …
…then why is it defined as the horizontal
movement of air?
Does the Earth stand still?
*The Coriolis Effect
* As the Earth rotates counterclockwise, the winds bend
and curve around the Earth.
* Gustave-Gaspard Coriolis,
an engineer and
mathematician, described this effect as an inertial
force in 1835.
*The Coriolis Effect
* In the Northern Hemisphere,
winds bend
to the right of their direction of travel.
* In the Southern Hemisphere, winds bend
to the left of their direction of travel.
* Let’s try a little investigation to see how
this works.
*Weather patterns and systems move
in a circular motion due to the
bending of the winds caused by the
Earth’s rotation.
*The Coriolis Effect
*Equilibrium
* Our Earth is always seeking balance.
* In an effort to find balance, there is a
continuous cycle of patterns.
* What is the driving force behind the
changes that create these patterns?
How are winds produced?
*Reflection Question
Ocean Currents
Warm currents flow away from the
equator.
Cold currents flow toward the equator.
*Ocean Currents
*Factors Influencing
Currents
*Sun
*Wind
*Coriolis
*Gravity
*Sun
*Energy from the Sun heats the water.
*Warm water is less dense that cold
water.
*Warm water rises, and cold water
sinks.
*As warm water rises, cold water moves
it to replace it.
*Convection Cycle
*Wind
*Just as wind moves from high pressure
to low pressure areas, so does the
water.
*Winds blow across the surface of the
water, causing friction.
*The water piles up because the surface
currents flow slower than the winds.
*Wind
*Gravity
* As water piles up and flows from high
pressure to low pressure, gravity will pull
down on the water.
* This forms vertical columns or mounds of
water.
* The Coriolis Effect causes the water to
curve.
*The Coriolis Effect
*Causes water to move to the right in
the Northern Hemisphere
*Causes water to move to the left in
the Southern Hemisphere
*The Coriolis Effect
*Make up 10% of oceans’ water
*Up to maximum depth of 400 m
*Surface ocean currents are caused by
the surface wind patterns.
*Surface Currents
*Surface Currents
*Gyres
 Vertical columns or mounds of water at the
surface and flow around them
 Produce enormous circular currents
 Five major locations:
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
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North Pacific - clockwise
South Pacific - counterclockwise
Indian Ocean - counterclockwise
South Atlantic - counterclockwise
North Atlantic - clockwise
*Oceanic Gyres
*Gulf Stream
* A strong surface current
* Begins at the tip of Florida
* Flows up the eastern coastline of the
U.S.
* Crosses the Atlantic Ocean
* Causes warmer climate in NW Europe
*Upwelling
*Surface waters blow to the right of
the wind.
*As less dense, surface water moves
off shore, cold, deep, denser waters
come to the surface to replace
them.
*Upwelling
*The Great Ocean
Conveyor:
Helps maintain Earth’s
Balance
*Deep Water
Currents
* Make up about 90% of oceans’ water
* Differences in density cause them to move.
* Differences in density are related to temperature
and salinity.
* At high latitudes, they sink deep into the ocean
basins.
* Temperatures are so cold, they cause the density to
increase.
*How are ocean currents
produced?
*Reflective Question
*El Nino
Abnormally high surface ocean
temperatures off the coast of South
America
Causes unusual weather patterns
across
the globe
*El Nino
* Starts because the easterly trade winds
weaken and allow the warm waters in the
Western Pacific to move east toward South
America
* This changes where the convection current
occurs.
* Causing rain where it usually doesn't occur
and drought where it usually rains
*El Nino Winter
*El Nino Summer
*La Nina
Abnormally low surface ocean
temperatures off the coast of South America
Causes unusual weather patterns across
the globe
*Ocean’s Effect on
Climate
* Ocean currents move more slowly than winds.
* Oceans hold more heat than the atmosphere and
land.
* Cold currents will cause nearby coastlines to be
cooler.
* Warm currents will cause nearby coastlines to be
warmer.
Where do the cold currents come from? The
warm currents?
*Predictable Patterns
How do these currents affect the
climate of the coastline?
*Reflection Questions
*How do our oceans impact
climate?