Lesson Outline

1
Lesson Outline
I. The Atmosphere
II. Solar Radiation the Global Energy Budget
III. Global Heat Transfer
IV. The Physics of Ideal Gases
V. Vertical Air Motion
VI. Atmospheric Circulation
VII. Cyclones
VIII. El Niño
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The Ocean, Atmosphere, and Climate

• The ocean and atmosphere interact by exchanging
  heat, water, and momentum.

The oceans cover more than 70 of the earths
surface and contain about 97 of its surface
water, which store a vast amount of heat energy.
The heat rises from the oceans, warming the
atmosphere and creating temperature gradients
that drive winds.
The winds in turn push against the sea surface
and set in motion ocean surface currents.
This coupled system of atmospheric and oceanic
circulation patterns distribute the heat and
regulate the climate around the earth.
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The Atmosphere

• The atmosphere is an envelope of gases
  surrounding the earth that extends approximately
  100120 kilometers into space.

The troposphere is where clouds form and weather
systems propagate, often controlled by the jet
stream.
The temperature increase in the stratosphere is
caused the absorption of ultraviolet radiation as
it enters the atmosphere.
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Composition of the Atmosphere

• The earths atmosphere is a mixture of gases.

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Solar Radiation

• Solar radiation reaching the outer edge of the
  atmosphere (red)

• 49 is in the visible range (400 ? 700
  nanometers).

• 9 is shortwave ultraviolet radiation (? lt 400
  nanometers)

• 42 is infrared longwave radiation (? gt 700
  nanometers) such as radiant heat.

Solar radiation penetrating into the atmosphere
may be reflected back into space, absorbed, or
pass through to the earths surface.
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Ultraviolet Radiation and Ozone

• In the upper atmosphere, ultraviolet (UV) rays
  collide with oxygen molecules (O2) to form ozone
  (O3).

This process results in the ozone layer of the
stratosphere.
The formation of ozone absorbs UV energy entering
the atmosphere.
Most of the UV energy is absorbed when ozone is
broken down into oxygen.
Without the ozone layer to filter out the UV
radiation, living organisms on Earth would have
to develop an armor to protect surface tissue
cells from UV damage.
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The Greenhouse Effect

• Most of the visible light passes through the
  atmosphere and is absorbed or reflected at the
  earths surface.

The light energy warms the earths surface, and
the heat energy produced is radiated back into
the atmosphere as longwave infrared radiation.
Most of this back radiation is absorbed again by
the atmosphere.
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Earths Energy Budget

• The earth must balance the incoming solar
  radiation with the loss of longwave radiation
  back into space.

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Angle of Incidence

• The energy budget for any specific region on the
  earth is usually unbalanced, the result of
  differential heating by the sun.

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Differential Heating on the Earth

• In equatorial regions, more solar radiation is
  absorbed than is returned to space, creating a
  heat surplus.

In polar regions, more energy is radiated back
into space than is absorbed, creating a heat
deficit.
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Advection

• In order to balance the energy budget, the ocean
  and the atmosphere transport excess heat from the
  lower latitudes toward the poles.

The transport of the properties of a fluid (such
as heat) by horizontal motion is called
advection.
Surface ocean waters near the equator are warmed
by the sun and transported toward the poles by
currents.
The warm currents, like the Gulf Stream, flow
poleward where excess heat is radiated back to
the atmosphere.
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Oceanic Heat Transport

• The warmer air surrounding these currents
  moderates the climates of nearby continental land
  masses.

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Atmospheric Heat Transport

• The excess heat not carried off by ocean currents
  is transported poleward by the atmosphere by two
  methods.

Advection. Winds transport warm air to higher
latitudes where excess heat is eventually
radiated back into space.
Evaporation and Precipitation. The evaporation
of water at one latitude and its precipitation at
a higher latitude transports heat energy toward
the pole.
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Ocean Atmospheric Heat Transport

• The relative importance of oceanic and
  atmospheric transport of heat depends on
  latitude.

At low latitudes (10º 15º), the ocean
transports 60 to 75 of the total heat.
At around latitude 30º, they transport an equal
amount of heat.
North of latitude 60º, nearly all the heat
transport is by the atmosphere.
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Motion of Gases

• A gas will diffuse (spread out) to fill any
  container.

The molecules of gas inside the container are in
constant motion, bouncing off the surfaces that
constrain them.
Every time a molecule hits a surface, it gives up
a small amount of heat energy as it rebounds to
hit another surface.
The constant bouncing off the walls creates a
pressure against the sides of the container, and
the pressure is equal all around that container.
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Ideal Gas Law

• The relationships between the pressure P,
  temperature T, and volume V, of a gas are
  described by the ideal gas law

where k is a gas constant and T is measured on
the Kelvin scale.
On the Kelvin scale, T 0 corresponds to
absolute zero, in which molecular motion ceases.
The relationship between the Kelvin and Celsius
scales is given by
K C 273 or C K 273.
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Example

• Suppose the pressure, temperature, and volume of
  an ideal gas contained in a cylinder are observed
  to be P 5 atm, V 6 L and T 27º C.

(a) Use the ideal gas law to find the constant k
for this gas.
Convert 27º C to Kelvin
K 273 C 300
Apply the Ideal Gas Law
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Example
Suppose the pressure, temperature, and volume of
an ideal gas contained in a cylinder are observed
to be P 5 atm, V 6 L and T 27º C.
(b) Suppose that when the volume of the cylinder
is increased to V 10 L the pressure is
decreased to P 2 atm. Find the resulting
temperature (in degrees Celsius).
gas constant is same
19
Vertical Air Motion

• Consider a scenario in which prevailing winds
  force a mass of dry air to blow over a mountain.

As the altitude of the air mass increases, the
surrounding pressure decreases, allowing the air
mass to expand.
In turn, the expansion of the air causes it to
cool.
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Vertical Air Motion
Consider a scenario in which prevailing winds
force a mass of dry air to blow over a mountain.
The process is reversed as the wind pushes the
air mass down the opposite side of the mountain.
The pressure increases as the air descends to a
lower altitude, the air mass contracts, and the
temperature of the air warms.
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Dew Point and Relative Humidity

• The amount of water vapor that a wet air mass can
  store is determined by its temperature the
  higher the temperature, the more moisture air can
  hold.

The point at which an air mass can hold no more
water vapor at its current temperature is called
the saturation point.
The temperature to which an air mass must be
cooled at constant pressure to reach saturation
is known as the dew point.
The relative humidity is the amount of water
vapor in the air at any moment compared to the
maximum it could hold at that temperature,
usually expressed as a percentage.
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Orographic Lifting

• Consider the case in which winds force a mass of
  wet air over a mountain.

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Convection

• Vertical air movement is also caused by
  convection, the vertical motion that occurs when
  a fluid such as air or water is heated from
  below, causing the density of the fluid to
  decrease.

The land and sea breezes experienced along a
coastline are a result of this process.
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Hadley Cells

• Air rising from the equator cools and sinks
  around 30º (the horse latitudes).

After sinking, some of the air returns to the
equator to complete a Hadley cell.
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Ferrel and Polar Cells

• The rest of the descending air continues poleward
  until around latitude 50º, the air mass is again
  uplifted by cold dense air from the polar
  regions.

Some of this rising air returns to the 30º
parallel to complete a Ferrel cell.
The remaining air travels to the pole where it
cools, sinks, and returns to form a polar cell.
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Evaporation, Precipitation, Salinity

• The effects of the Hadley and Ferrel cells are
  observable in the in the precipitation,
  evaporation, and salinity patterns around the
  globe.

In regions of rising moist air, precipitation
exceeds evaporation and rainfall reduces the
salinity of surface water.
In regions of descending dry air, evaporation
exceeds precipitation and water is removed from
the ocean surface layer, increasing the salinity.
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Coriolis Deflection

• Because the earth is a sphere, the surface of the
  earth is spinning through space at different
  rates from the equator to the pole.

An object moving across latitudes will carry its
original momentum with it, causing an apparent
bending in its path.
The bending is called the Coriolis deflection,
and the acceleration that produced it is known
as the Coriolis acceleration.
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Coriolis Deflection

• Coriolis Deflection is nicely illustrated by a
  simple game of catch between two people on a
  merry-go-round.

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Global Wind Patterns

• A realistic description of global atmospheric
  circulation emerges when the effects of rotation
  are added to the three circulation cells.

As the surface air masses of the Hadley cells
between 30º N and 30º S approach the equator they
are deflected westward by the Coriolis force to
form the system of surface winds known as the
trade winds.
The northeast trade winds and the southeast trade
winds are separated by the intertropical
convergence zone (ITCZ), or doldrums.
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Hurricane Formation

• By early summer, ocean surface temperatures in
  the tropics have warmed and the ITCZ, which
  varies position throughout the year, usually
  shifts northward of the equator.

When a low-pressure disturbance develops in the
ITCZ and is carried westward by the trade winds,
conditions are favorable for cyclogenesis.
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Conditions for Hurricane Development

• Warm sea surface temperatures of 27º C or more to
  a depth of least 50 meters.

• Sufficient Coriolis force to torque the winds
  into the spiraling motion necessary to maintain
  the low pressure center.

• Low vertical wind shear between the sea surface
  and the upper troposphere.

• An unstable atmosphere and high relative humidity
  several miles above the sea surface.

• High pressure aloft to exhaust vertical air flow.

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Effects of Hurricanes on Pinellas County
Storm surge 4-5 feet
Storm surge 6-8 feet
Storm surge 9-12 feet
Storm surge 13-18 feet
Storm surge 18 feet
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El Niño/Southern Oscillation

• El Niño, an abnormal warming of surface ocean
  waters in the eastern tropical Pacific, is one
  part of what scientists refer to as the Southern
  Oscillation.

The Southern Oscillation is an alternating
pattern of surface air pressure between the
eastern and western tropical Pacific.
Because the ocean warming and pressure reversals
usually occur together, they are jointly known as
the El Niño/Southern Oscillation (ENSO).
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Conditions in the Tropical Pacific

• Normally, the Pacific trade winds blow strongly
  from a high-pressure zone in the eastern Pacific
  to a low-pressure zone in the western Pacific.

The trades push warm surface waters westward into
the western Pacific warm pool. In the east cold,
nutrient-rich waters upwell.
The trades tend to lose strength with the onset
of spring and, as a result, waters in the central
and eastern Pacific start to heat up.
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El Niño Conditions

• Every three to seven years, however, the pressure
  gradient that controls the trade winds breaks
  down, causing them to weaken or even reverse
  direction.

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El Nino Sea Surface Temperatures

• With the weakened winds, warm surface waters from
  the western Pacific move eastward.

The natural springtime warming in the central
Pacific is allowed to continue and also spread
eastward through the summer and fall right up to
the coast of Peru.
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Impact on Climate

• The Earths atmosphere responds to an El Niño by
  producing patterns of high and low pressure that
  have a profound impact on weather around the
  globe

Droughts and forest fires in the tropical
rainforests of Indonesia and flooding in the
deserts of Peru.
Higher temperatures in western Canada and the
upper plains of the US colder temperatures in
the southern US.
Drought along the east coast of southern Africa.
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La Niña

• The opposite phase of an El Niño, La Niña is
  characterized by unusually cold ocean
  temperatures in the Equatorial Pacific.

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La Niña Effects on Climate

• La Niñas impacts on weather tend to be opposite
  those of El Niño.

Wet weather returns to Indonesia and dry
conditions to Peru.
Winters are drier and warmer than normal in the
Southeast US and cooler than normal in the
Northwest and Canada.
The east coast of southern Africa experiences a
cooler, wetter summer.
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El Niño Periods

• Eventually within one or two years, normal
  atmospheric pressure gradients are restored, the
  trade winds are reestablished in the tropical
  Pacific, the warm pool retreats to the western
  Pacific, and cold, nutrient-rich waters return to
  the coast of Peru.