Solar Radiation - initial source of energy to the Earth. It can be absorbed, reflected and reradiated. The redistribution of this energy controls the structure and dynamics of the Atmosphere and Oceans.

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Chapter 8 Circulation of the Atmosphere
Solar Radiation - initial source of energy to the
Earth. It can be absorbed, reflected and
reradiated. The redistribution of this energy
controls the structure and dynamics of the
Atmosphere and Oceans.
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The Atmosphere Moves in Response to Uneven Solar
Heating and Earths Rotation

• An estimate of the heat budget for Earth. On an
  average day, about half of the solar energy
  arriving at the upper atmosphere is absorbed at
  Earths surface. Light (short-wave) energy
  absorbed at the surface is converted into heat.
  Heat leaves Earth as infrared (long-wave)
  radiation. Since input equals output over long
  periods of time, the heat budget is balanced.

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Earths Uneven Solar Heating Results in
Large-Scale Thermal Cell type of Atmospheric
Circulation
A convection cell is driven by density differences

• A convection current forms in a room when air
  flows from a hot radiator to a cold window and
  back.
• Air warms, expands, becomes less dense, and rises
  over the radiator. Air cools, contracts, becomes
  more dense, and falls near the cold glass window.

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Earths Uneven Solar Heating Results in
Large-Scale Atmospheric Circulation

• What factors govern the global circulation of
  air?
• Uneven solar heating
• The Coriolis effect

• The Coriolis effect is the observed deflection of
  a moving object, caused by the moving frame of
  reference on the spinning Earth.
• How does this apply to the atmosphere?
• As air warms, expands, and rises at the equator,
  it moves toward the pole, but instead of
  traveling in a straight path, the air is
  deflected eastward.
• In the Northern Hemisphere air turns to the
  right.
• In the Southern Hemisphere air turns to the left.

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The Coriolis Effect Influences the Movement of
Air in Atmospheric Circulation Cells

• Global air circulation as described in the
  six-cell circulation model. Air rises at the
  equator and falls at the poles, but instead of
  one great circuit in each hemisphere from equator
  to pole, there are three in each hemisphere. Note
  the influence of the Coriolis effect on wind
  direction. The circulation show here is idea
  that is, a long-term average of wind flow.

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Wind bands Three convection cells in each
hemisphere Trade winds NE (30N to 0) and SE
(30S to 0) Westerlies 60N to 30N and 60S
to 30S Polar easterlies 90N to 60N and 90S
to 60S Low pressure at 0, 60N, and 60S Low
pressure, ascending air, clouds, increased
precipitation High pressure at 30N, 30S,
90N, and 90S High pressure, descending air,
clear skies, low precipitation
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The Coriolis Effect Influences the Movement of
Air 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 within cells?
• Doldrums are calm equatorial areas where two
  Hadley cells converge
• Horse latitudes are areas between Hadley and
  Ferrel cells.
• Trade winds are surface winds of Hadley cells.
• Westerlies are surface winds of Ferrel cells.

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Sea Breezes and Land Breezes Arise from Uneven
Surface Heating

• The flow of air in coastal regions during stable
  weather conditions.
• (a) In the afternoon, the land is warmer than the
  ocean surface, and the warm air rising from the
  land is replaced by an onshore sea breeze.
• (b) At night, as the land cools, the air over the
  ocean is now warmer than the air over the land.
  The ocean air rises. Air flows offshore to
  replace it, generating an offshore flow (a land
  breezes).

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In the Northern Hemisphere Air flows clockwise
around high pressure systems Air flows
counterclockwise around low pressure systems
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Storms Are Variations in Large-Scale Atmospheric
Circulation

• Storms are regional atmospheric disturbances.
  Storms have high winds and most have
  precipitation.
• Tropical cyclones occur in tropical regions.
  These storms can cause millions of dollars worth
  of damage and endanger life.
• Extratropical cyclones occur in Ferrel cells, and
  are winter weather disturbances. These storms can
  also cause extensive damage.
• Both types of storms are cyclones, or rotating
  masses of low-pressure air.

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Extratropical Cyclones Form between Two Air Masses

• (a) The genesis and early development of an
  extratropical cyclone in the Northern Hemisphere
• (b) How precipitation develops in an
  extratropical cyclone. These relationships
  between two contrasting air masses are
  responsible for nearly all the storms generated
  in the polar frontal zone and thus responsible
  for the high rainfall within these belts and the
  decreased salinities of surface waters below.

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Tropical Cyclones Form in One Air Mass

• The tracks of tropical cyclones. The breeding
  grounds of tropical cyclones are shown as
  orange-shaded areas. The storms follow curving
  paths First they move westward with the trade
  winds. Then they either die over land or turn
  eastward until they lose power over the cooler
  ocean of mid-latitudes. Cyclones are not spawned
  over the South Atlantic or the southeast Pacific
  because their waters are too chilly nor in the
  still air - the doldrums - within a few degrees
  of the equator.

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Chapter 8 - Summary
The interaction of ocean and atmosphere moderates
surface temperatures, shapes Earth's weather and
climate, and creates most of the 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 the atmosphere and leads to
areas of different atmospheric pressures. The
direction of air flow in these currents is
influenced by the rotation of Earth. To
observers on the surface, Earth's rotation causes
moving air (or any moving mass) in the Northern
Hemisphere to curve to the right of its initial
path, and in the Southern Hemisphere to the left.
This is known as the Coriolis effect.
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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 these
cells is influenced by Earths rotation (Coriolis
effect). Each hemisphere has 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 boundary between air
masses. Tropical cyclones, the most powerful of
Earth's atmospheric storms, occur within a single
humid air mass.
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Chapter 9 Circulation of the Ocean
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Surface Currents Are Driven by the Winds
The westerlies and the trade winds are two of the
winds that drive the oceans surface
currents. About 10 of the water in the world
ocean is involved in surface currents, water
flowing horizontally in the uppermost 400 meters
(1,300 feet) of the oceans surface, driven
mainly by wind friction. (left) Winds, driven by
uneven solar heating and Earths spin, drive the
movement of the oceans surface currents. The
prime movers are the powerful westerlies and the
persistent trade winds (easterlies).
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Surface Currents
What are some effects of ocean currents? Transfer
heat from tropical to polar regions Influence
weather and climate Distribute nutrients and
scatter organisms Surface currents are driven
by wind Most of Earths surface wind energy is
concentrated in the easterlies and
westerlies. Due to the forces of gravity, the
Coriolis effect, and winds, water often moves in
a circular pattern called a gyre.
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Surface Currents Are Driven by the Winds

• The gyres circulate clockwise in the Northern
  Hemisphere and counterclockwise in the Southern
  Hemisphere.

• The North Atlantic gyre, a series of four
  interconnecting currents with different flow
  characteristics and temperatures.

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Surface Currents Flow around the Periphery of
Ocean Basins

• Surface water blown by the winds at point A will
  veer to the right of its initial path and
  continue to the east.
• Water at point B veers right and continues to the
  west.

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Surface Currents Flow around the Periphery of
Ocean Basins

• The Ekman spiral and the mechanism by which it
  operates.

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Surface Currents Flow around the Periphery of
Ocean Basins
Consider the North Atlantic.
The surface is raised through wind motion and
Ekman transport to form a low hill. The
westward-moving water at B feels a balanced
pull from two forces the one due to Coriolis
effect (which would turn the water to the right)
and the one due to the pressure gradient, driven
by gravity (which would turn it to the left).
The hill is formed by Ekman transport. Water
turns clockwise (inward) to form the dome, then
descends, depressing the thermocline.
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Seawater Flows in Six Great Surface Circuits

• Geostrophic gyres are gyres in balance between
  the pressure gradient and the Coriolis effect. Of
  the six great currents in the worlds ocean, five
  are geostrophic gyres. Note the western boundary
  currents in this map.

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Boundary Currents Have Different Characteristics

• Western boundary currents These are narrow,
  deep, warm, fast currents found at the western
  boundaries of ocean basins.
• The Gulf Stream
• The Japan Current
• The Brazil Current
• The Agulhas Current
• The Eastern Australian Current
• Eastern boundary currents These currents are
  cold, shallow and broad, and their boundaries are
  not well defined.
• The Canary Current
• The Benguela Current
• The California Current
• The West Australian Current
• The Peru Current

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Boundary Currents Have Different Characteristics

• Eddy formation
• The western boundary of the Gulf Stream is
  usually distinct, marked by abrupt changes in
  water temperature, speed, and direction.
• (a) Meanders (eddies) form at this boundary as
  the Gulf Stream leaves the U.S. coast at Cape
  Hatteras. The meanders can pinch off (b) and
  eventually become isolated cells of warm water
  between the Gulf Stream and the coast (c).
  Likewise, cold cells can pinch off and become
  entrained in the Gulf Stream itself (d). (C
  cold water, W warm water blue cold, red
  warm.)

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Boundary Currents Have Different Characteristics

• Water flow in the Gulf Stream and the Canary
  Current, parts of the North Atlantic gyre.

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Surface Currents Affect Weather and Climate

• Wind induced vertical circulation is vertical
  movement induced by wind-driven horizontal
  movement of water.
• Upwelling is the upward motion of water. This
  motion brings cold, nutrient rich water towards
  the surface.
• Downwelling is downward motion of water. It
  supplies the deeper ocean with dissolved gases.

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Nutrient-Rich Water Rises near the Equator

• Equatorial upwelling.
• The South Equatorial Current, especially in the
  Pacific, straddles the geographical equator.
  Water north of the equator veers to the right
  (northward), and water to the south veers to the
  left (southward). Surface water therefore
  diverges, causing upwelling. Most of the upwelled
  water comes from the area above the equatorial
  undercurrent, at depths of 100 meters or less.

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Wind Can Induce Upwelling near Coasts

• Coastal upwelling.
• In the Northern Hemisphere, coastal upwelling can
  be caused by winds from the north blowing along
  the west coast of a ccontinent. Water moved
  offshore by Ekman transport is replaced by cold,
  deep, nutriend-laden water. In this diagram,
  temperature of the ocean surface is shown in
  degrees Celsius.

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Wind Can Also Induce Upwelling Coastal Downwelling

• Coastal downwelling.
• Wind blowing from the south along a Northern
  Hemisphere west coast for a prolonged period can
  result in downwelling. Areas of downwelling are
  often low in nutrients and therefore relatively
  low in biological productivity.

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El Niño and La Niña Are Exceptions to Normal Wind
and Current Flow
An El Niño Year
A Non-El Niño Year

• In an El Niño year, when the Southern Oscillation
  develops, the trade winds diminish and then
  reverse, leading to an eastward movement of warm
  water along the equator. The surface waters of
  the central and eastern Pacific become warmer,
  and storms over land may increase.
• In a non-El Niño year, normally the air and
  surface water flow westward, the thermocline
  rises, and upwelling of cold water occurs along
  the west coast of Central and South America.

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Thermohaline Circulation Affects All the Oceans
Water

• The movement of water due to different densities
  is thermohaline circulation.
• Remember that the ocean is density stratified,
  with the densest water at the bottom. There are
  five common water masses
• Surface water 0-200m
• Central water 200-thermocline
• Intermediate water thermocline-1500m
• Deep water 1500-4000m
• Bottom water 4000-bottom

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• Thermohaline Circulation
• Vertical, density driven circulation, resulting
  from change in temperature and salinity

• Continuity of flow
• Water is a relatively fixed quantity in the
  oceans
• Water can not accumulate in one location or be
  removed from another location without movement of
  water between those locations
• Vertical movement of water
• Horizontal movement of water

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Chapter 9 - Summary

• Ocean water circulates in currents caused mainly
  by wind friction at the surface and by
  differences in water mass density beneath the
  surface zone.
• Water near the ocean surface moves to the right
  of the wind direction in the Northern Hemisphere,
  and to the left in the Southern Hemisphere.
• The Coriolis effect modifies the courses of
  currents, with currents turning clockwise in the
  Northern Hemisphere and counterclockwise in the
  Southern Hemisphere. The Coriolis effect is
  largely responsible for the phenomenon of
  westward intensification in both hemispheres.
• Upwelling and downwelling describe the vertical
  movements of water masses. Upwelling is often due
  to the divergence of surface currents
  downwelling is often caused by surface current
  convergence or an increase in the density of
  surface water.

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Chapter 9 - Summary

• El Niño, an anomaly in surface circulation,
  occurs when the trade winds falter, allowing warm
  water to build eastward across the Pacific at the
  equator.
• Circulation of the 90 of ocean water beneath the
  surface zone is driven by gravity, as dense water
  sinks and less dense water rises. Since density
  is largely a function of temperature and
  salinity, the movement of deep water due to
  density differences is called thermohaline
  circulation.
• Water masses almost always form at the ocean
  surface. The densest (and deepest) masses were
  formed by surface conditions that caused water to
  become very cold and salty.
• Because they transfer huge quantities of heat,
  ocean currents greatly affect world weather and
  climate.

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Period ( wavelength) and Wave Energy
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Deep- to Shallow-Water Waves
Progressive Waves
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Wave Speed
Keep in mind wave energy, NOT the water
particles move across the surface of the sea.
Wave propagates with C, energy moves with V
Wave Speed is C - Group Speed is
V wave speed wavelength / period or
C L / T T is determined by generating force so
it remain the same after the wave formed, but C
changes. In general, the longer the wavelength
the faster the wave energy will move through the
water.
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Deep Water Waves

• Period to about 20 seconds
• Wavelength to at most 600 meters (extreme)
• Speed to about 100 kilometers/hour (70 mi/hr)
  (extreme)

For example, for a 300 meters wave and 14 sec
period, the speed is about 22 meters per second
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Deep Water Waves
surface waves progressing in waters of D larger
than 1/2 L as the wave moves through, water
particles move in circular orbit diameter of
orbits decrease with depth, orbits do not reach
bottom, particles do not move below a depth D
L/2 The wave speed can be calculated from
knowledge of either the wavelength or the
wave period C 1.56 m/s2
T or C2 1.56 m/s2 L Group Speed (which
really transport the energy) is half of the
wave speed for deep-water waves
V C/2
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Shallow-Water Waves

• Seismic Sea Waves Shallow-Water Waves
• Period to about 20 minutes
• Wavelength of about 200 kilometers
• Speed of about 750-800 km/hr (close to 500
  mi/hr!!)

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• Shallow-Water Waves
• surface waves generated by wind and progressing
  in waters of D
• less than (1/20) L
• wave motion as the wave moves through, water
  particles move in
• elliptical orbits
• diameter of orbits remains the same with depth,
  orbits do reach the
• bottom where they flatten to just an
  oscillating motion back and
• forth along the bottom
• The wave speed and the wavelength are
  controlled by the depth D of the waters only
• 
  
• Group Speed (which transport the energy) is
  the same as the wave speed for shallow-water
  waves
• V C

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Wind Blowing over the Ocean Generates Waves Waves
development and growth are affected by
Wind Speed velocity at which the wind is
blowing Fetch distance over which the wind is
blowing Duration length of time wind blows
over a given area
Larger Swell Move Faster ? waves separate into
groups wave separation is called dispersion
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• Storm centers and dispersion
• Winds flow around low pressure
• Variety of periods and heights are generated ?
  grouped into wave trains

Waves with longer period (T) and larger length
move faster - these get ahead of the pack.
Wave sorting of these free waves is dispersion
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Wave Height, Wavelength Wave Steepness
Typical ratio wave height to wavelength in open
ocean 17 wave steepness angle of the crest
120 Exceed these conditions and wave will
break at sea ? whitecaps
Wave Height is controlled by (1) wind speed, (2)
wind duration and (3) fetch ( the distance over
water that the wind blows in the same direction
and waves are generated) Significant Wave Height
- average wave height of the highest one-third of
the waves measured over a long time
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Breaker Types
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Wave Refraction slowing and bending of waves as
they approach shore at an angle
part of wave in shallow water slows down
oblique angle between direction of motion of
waves and depth contours
part of same wave still in deep water hence faster
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Wave refraction- propagation of waves around
obstacles, for example over a shallow ridge
energy is focused (waves get interrupted, waves
generate other waves)
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Wave refraction in a shallow bay energy is
spread
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Wave Diffraction
narrow opening
diffraction and wave interaction
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when????

• Tsunamis
• Vertical sea floor displacement
• Shallow water waves
• Long wavelength
• Low period
• Wave height changes (quite dramatically!)
• At point of origin
• Close to shore where depth decreases