Download Circulation

Atmosphere and Ocean Interact
• Atmosphere: volume of gases, water vapor,
and airborne particles that surround Earth
• Water and gases are freely exchanged
between atmosphere and ocean
• Gases entering the atmosphere from the
ocean affect climate
• Gases entering the ocean from the
atmosphere can affect sediment deposition,
distribution of life, and physical characteristics
of seawater (CO2)
Atmosphere and Ocean Interact
• Water evaporated from the ocean is
moved by wind (mass movement of air)
and affects both weather and climate
• Weather: state of the atmosphere at a
specific time and place
– Sunny, rainy, cloudy, windy
• Climate: long term averages of
temperature and precipitation in a given
area
Composition of Atmosphere
• Composed mainly of:
– Nitrogen – 78%
– Oxygen – 21%
– Ar, CO2, Ne, He, CH4 – less than 1%
• Water vapor can occupy as much as 4% of
air’s volume
– Mostly invisible as vapor - humidity
– Can be visible as clouds or fog
Density of Air
• Density of air is influenced by temperature
and water content
• As air is heated, it expands, becomes less
dense and rises
– Warm air can also hold more vapor
• As air is cooled, it shrinks, becomes more
dense and sinks
– Cold air holds less water vapor – as air cools,
its water vapor condenses into clouds
• If enough condensation takes place, you get
precipitation
Solar Heating and the Atmosphere
• Atmospheric circulation is powered by
sunlight – drives wind
• 51% of solar energy is absorbed by Earth’s
land and water
Solar Heating and Latitude
• Not all areas on Earth get the same
amount of solar heating
• Poles get less solar heating due to the
amount of atmosphere the sunrays have to
travel through and also due to reflection
• Equator gets the most solar heating – direct
sunrays, very little reflection
Solar Heating and Latitude
Solar Heating and Seasons
• At different times
of year, places get
different amounts
of solar energy
• This is due to the
23.5 degree tilt of
Earth’s rotational
axis relative to the
plane of its orbit
around the sun
Solar Heating and Circulation
• The concentration of solar energy at the
equator affects the atmosphere
• Uneven solar heating causes convection
currents to form
– Air is heated at the equator, becomes less dense
and rises to high altitude
– The air then turns towards the poles
– At the poles, the air is cooled, becomes more
dense and sinks to the surface
– The air then turns back to the equator
• However, air does not travel directly
north/south – it travels at an angle due to the
Coriolis Effect
Solar Heating and Circulation
Coriolis Effect
• What is it?
– The apparent deflection of a moving object
due to the rotation of the Earth
• What does it cause?
– Causes air masses and water to move in a
clockwise direction in the N. Hemisphere and
counterclockwise in the S. Hemisphere
How Does the Coriolis Effect Work?
• Each city moves at a
rate of 15 degrees/hr
• However, the cities
move at diff speeds –
Buffalo moves
slower because it has
to travel less distance
in a 24 hr period
than Quito
How Does the Coriolis Effect Work?
How Does the Coriolis Effect Work?
• Imagine a massive moving object between the
two cities – a cannonball shot north from Quito
toward Buffalo
• The cannonball would not only be traveling
north, but it will also be traveling eastward at
1,668 km/hr (Quito’s eastward speed)
• So, as it goes north, it also veers to the right
(east) – clockwise direction
• Will it land in Buffalo?
– No – Buffalo doesn’t move at the same speed as Quito
– The cannonball will land ahead of Buffalo since
Buffalo moves at a slower rate
How Does the Coriolis Effect Work?
• Now take a second cannonball. Shoot it south
from Buffalo to Quito. What will happen?
• Not only will it travel south, it will veer to the
right again (this time to the west or clockwise) at
a speed of 1,260 km/hr.
• Will it land in Quito?
– No – Quito travels at a different speed
– The cannonball will land behind Quito since Buffalo
travels slower and the ball was moving at a slower
rate
Coriolis Effect Video
• http://www.youtube.com/watch?v=mcPs_
OdQOYU
• http://www.classzone.com/books/earth_sci
ence/terc/content/visualizations/es1904/es1
904page01.cfm?chapter_no=visualization
Coriolis Effect and the Atmosphere
• The Coriolis Effect causes atmospheric
circulation cells to form
• Convection currents still play a huge role in
the rising and sinking of air
• However, due to the Coriolis Effect, the air
is deflected eastward as is moves towards
the poles
– It turns to the right (clockwise) in the N.
Hemisphere
– It turns to the left (counter clockwise in the S.
Hemisphere
Circulation Cells in the Atmosphere
• Due to changes in air density from
precipitation and changes in temperature,
air can’t travel all the way from the
equator to the poles.
• This causes air to sink at 3 latitudes: 30˚
N/S, 60˚ N/S, and at the poles
Circulation Cells in the Atmosphere
• There are 3 pairs of circulation cells
• Hadley Cells
– Occur from 0˚-30˚ N/S of the Equator
• Ferrel Cells
– Occur from 30˚-60˚ N/S
• Polar Cells
– Occurs above 60˚ N/S
Atmospheric Circulation Cells
Atmospheric Circulation Cells and
Wind Patterns
• At boundaries between circulation cells, air
is moving vertically and surface winds are
weak
– Occur where the 2 Hadley cells meet – called
the doldrums
• Also known as the Intertropical Convergence Zone
• Contributes to the success of tropical rain forests
– Also occurs where the Hadley and Ferrel cells
meet – called the horse latitudes
• Contributes to desert-like climates
Atmospheric Circulation Cells and
Wind Patterns
• Within each cell, there is dependable
surface winds that blow almost constantly
• Trade winds (aka – the easterlies)
– Surface winds of the Hadley cells
– Centered at 15˚N and 15˚S
– Winds move toward the equator
• Westerlies
– Surface winds of the Ferrel cells
– Centered at 45˚N and 45˚S
Atmospheric Circulation Cells and
Wind Patterns
Monsoons
• A monsoon is a pattern of wind circulation
that changes with the season
• Areas subject to monsoons generally have wet
summers and dry winters
• What causes monsoons?
– In the spring, land heats more rapidly than the
adjacent ocean.
– The air above the land becomes warmer and rises
– Relatively cool air flows from the ocean to the
land to replace the warm air that had risen
– Continued heating causes this humid air to rise,
condense, and form clouds and rain
Sea Breezes and Land Breezes
• Small, daily mini-monsoons
• Morning sunlight doesn’t warm the ocean
as much as the land
• The warmer inland rocks transfer heat to
the air, which expands and rises, creating a
zone of low atmospheric pressure over the
land; cooler air from over the sea then
moves toward land  sea breeze
• Situation reverses after sunset  land
breeze
Sea Breezes
Cool air
descends
Warm air ascends
Land warmer than
sea; breeze flows
onshore
Storms
• Storms are regional atmospheric
disturbances characterized by strong winds
accompanied by precipitation
• Cyclones – huge rotating masses of lowpressure air in which winds converge and
ascend
– Tropical cyclones – originate in the tropics and
travel poleward
– Extratropical cyclones – originate in the Ferrel
cells (“extra” means outside)
Storms and Air Masses
• Cyclones form between or within air
masses
– Air mass – a large body of air with uniform
temperature, humidity, and density
• Air that pauses over land or water tends to
take on the characteristics of the surface
below
– i.e. cold, dry land causes the air to become
cold and dry
Storms and Air Masses
• Air masses can move within or between
circulation cells, however, air masses
cannot mix with each other due to density
differences
• When 2 air masses meet, the denser air
slides under the lighter air mass, lifting the
lighter one and causing its air to expand
and cool causing water vapor to condense
• The boundary between air masses is called
a front
Extratropical Cyclones
• Form at the boundary between the Polar
and Ferrel cells – the polar front
• Occur mainly in the winter when
temperature and density differences are
more pronounced
• Turns counter clockwise in the N.
Hemisphere and clockwise in the S.
Hemisphere
Extratropical Cyclones
Tropical Cyclones
• Great masses of warm, humid, rotating air
• Occur in all tropical oceans except the
equatorial S. Atlantic
• Large tropical cyclones are called a variety of
names depending on origin:
–
–
–
–
Hurricanes – N. Atlantic and E. Pacific
Typhoons – W. Pacific
Tropical cyclones – Indian Ocean
Willi-willis – near Australia
• Winds must reach 74mph in order to be
called a hurricane
– About 100 reach this status every year!
Tropical Cyclones
Tropical cyclones develop in zones of high humidity and warm air over sea
surfaces with temperatures above 26ºC (79ºF), which are shown in red in the
satellite image above.
Origins/Paths of Tropical Cyclones
As tropical storms move westward on the trade
winds, they veer northward towards the poles
and then hit land or move out to the ocean
going eastward, where the storms die.
Hurricanes
• May be up to 620 miles in diameter
• Can be over 9 miles high
• The eye (or center) of the hurricane can be
8-10 miles in diameter
• Forms between 10˚ and 25˚ latitude in
both hemispheres where the water is warm
and the atmosphere is both warm and
humid
Hurricanes
Rising winds exit
from the storm at
high altitudes.
The calm central
eye usually is about
24 kilometers
(15 miles) wide.
Gales circle the eye at speeds
of up to 320 kilometers
(200 miles) per hour.
Moist surface winds
spiral in towards the
center of the storm
Rotation of Hurricanes
• Rotate counterclockwise in the N.
Hemisphere
• Rotate clockwise in the S. Hemisphere
• Does this mean the that Coriolis effect does
not apply to tropical cyclones? NO
– The opposite rotation is caused by the Coriolis
deflection of winds approaching the center of
a low pressure area from great distance
– In the N. Hemisphere, the approaching air is
deflected rightward, which causes the storm to
spin counter clockwise
Rotation of Hurricanes
Hurricane Katrina - 2005
Hurricane Katrina - 2005
Katrina
25 ft
storm surge
Hurricane Ike - 2008
Ike Aftermath –
Galveston, TX
15-20 ft storm surge
Storm Damage
• Three types
• Wind
• Rain
• Storm Surge = mass of waves driven by storm
winds
• Which is the biggest problem?
• Storm surge
Storm Surges
• Abrupt bulge or dome of water driven ashore
by a hurricane
• The dome becomes bigger as the surge enters
shallower water
– The only way for the water to go is up
• Bigger storms = bigger storm surges
• All of this water does not come ashore as one
wave. Instead, it rushes on land in what looks
like a series of large waves or sometimes looks
like high tide is moving in rapidly
Storm Surges
http://www.nhc.noaa.gov/surge/animations/hurricane_stormsurge.swf