Weather and Climate

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Weather and Climate
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What is Energy?

• By definition, energy is the ability or capacity
  to do work on some form of matter.
• Energy comes in many different forms
• Kinetic energy
• Potential energy
• Radiant energy
• Chemical energy
• Electric energy
• Magnetic energy

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Potential Energy

• The energy that a body possesses by virtue of its
  position with respect to other bodies in the
  field of gravity.
• Huh?
• PEmgh
• Where mmass of object,
• g gravity
• hheight of object above ground

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Kinetic Energy

• The energy within a body that is the result of
  its motion.
• KE1/2mv2
• Where mmass of object
• vvelocity of object
• If a volume of water and an equal size volume of
  air were moving at the same speed, which would
  have the greater kinetic energy?

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1st Law of Thermodynamics

• Energy cannot be created nor can it be
  destroyed.
• Energy can change form
• that is, the energy lost during one process must
  equal the energy gained during another.

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Temperature

• Temperature is a measure of the average speed of
  atoms and molecules comprising a matter.
• Higher Temperature gt Faster Molecules
• Lower Temperature gt Slower Molecules
• Temperature is a measure of the average kinetic
  energy.

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Temperature Scales

• If we allowed some molecules to cool to a point
  where they no longer had any motion, that point
  would be called absolute zero.
• At absolute zero there is a minimum amount of
  energy, and theoretically no thermal motion.
• Absolute zero is
• -459 oF (Fahrenheit)
• -273oC (Celsius)
• 0 K (Kelvin)

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Kelvin Scale

• This scale begins at absolute zero, so there are
  no negative numbers in this scale.
• Introduced by a British scientist, Lord Kelvin.
• Has the same increment as the celsius scale.
• K oC 273
• Example -20 oC ? In Kelvin
• Answer -20 oC 273 253 K

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Fahrenheit ltgt Celsius

• An increment of 1 oC is equal to an increment of
  1.8 oF.
• oC 5/9 (oF 32)

Example 50 oF ? oC Answer 5/9 (50 32) 10
oC

• oF 9/5 oC 32

Example -5 oC ? oF Answer 9/5(-5) 32 23
oF
Math Review
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What is heat?

• Heat is energy in the process of being
  transferred from one object to another because of
  the temperature difference between the the two
  objects.

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Heat Capacity

• Heat capacity is the ratio of the heat absorbed
  (released) by a system to the corresponding
  temperature rise (fall).
• Water has a high heat capacity/specific heat.

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What is latent heat?
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Sensible Heat

• Sensible heat is the heat we can feel and
  measure with a thermometer.

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How is heat transferred in the Atmosphere?

• Conduction
• Convection
• Advection
• Radiation
• Energy propagated in the form of electro-magnetic
  waves

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Conduction
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How is heat transferred in the Atmosphere?

• Conduction
• Convection
• Advection
• Radiation
• Energy propagated in the form of electro-magnetic
  waves

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Convection
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How is heat transferred in the Atmosphere?

• Conduction
• Convection
• Advection
• Radiation
• Energy propagated in the form of electro-magnetic
  waves

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Advection
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In Class Activity
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How is heat transferred in the Atmosphere?

• Conduction
• Convection
• Advection
• Radiation
• Energy propagated in the form of electro-magnetic
  waves

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Types of Radiation
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Can we see this radiation being emitted?

• Not with our eyes, unless it is very hot!

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Stefan-Boltzmann Law

• E sT 4
• Objects at a higher temperature emit radiation at
  a greater rate.
• gt As the temperature of an object increases,
  more total radiation is emitted per second.

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Sun Vs. Earth

• The surface temperature of the sun is 6000K
  (10,500 oF).
• The surface temperature of the earth is 288 K
  (59 oF).
• lmax constant/T
• The above equation known as Weins Law allows us
  to determine the maximum wavelength at which the
  sun and earth emit radiation.

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Sun Vs. Earth

• SUN gt 0.5 mm
• (shortwave radiation)
• EARTH gt 10 mm
• (longwave radiation)

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The Suns Electromagnetic Spectrum

• While the sun has a maximum emitted at .5 mm, it
  still emits at almost all other wavelengths.

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If the earth and everything on the earth are
continually emitting radiation, why is the earth
not getting progressively colder?
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• Objects not only emit radiation, but also absorb
  radiation!

If an object Emits gt Absorbs gt cools Emits lt
Absorbs gt warms Emits Absorbs gt no change
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What affects the rate at which something emits
and absorbs radiation?

• Depends strongly on surface characteristics
• Color
• Texture
• Moisture
• Temperature

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Blackbodies

• Definition Any object that is a perfect absorber
  and a perfect emitter.
• Perfect absorber Absorbs all radiation that
  strikes it.
• Perfect emitter Emits the max. radiation
  possible at the given temperature.

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Radiative Equilibrium

• The sun constantly bathes the earth in radiation.
• Earth is constantly emitting infrared radiation.

• The average temperature at which this occurs is
  called the radiative equilibrium temperature.

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Selective Absorbers

• Objects that selectively absorb and emit
  radiation, such as the gases in our atmosphere.
• Our atmosphere absorbs some wavelengths of
  radiation, and is transparent to others.

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Why dont we get sunburned through a window?

• Glass is a selective absorber.
• Glass absorbs some infrared and ultraviolet
  radiation.
• Glass does not absorb visible light wavelengths

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Why can you get sunburned on cloudy days?
Clouds are also selective absorbers!
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• Infrared radiation is absorbed by greenhouse
  gases.
• Clouds can absorb in the atmospheric window,
  where CO2 and H2O dont.

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Kirchhoffs Law

• Objects that selectively absorb radiation also
  selectively emit radiation at the same
  wavelength.
• Definition Good absorbers are good emitters at a
  particular wavelength, and poor absorbers are
  poor emitters at the same wavelength.

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Lets Look at how Kirchhoffs law works on
earth.
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How does color fit into all this talk about
absorption and emittence?

• Why is it hard to tell in the dark what color
  your crayon is?
• Color does NOT represent the wavelengths at which
  an object is emitting.
• Color represents the wavelengths that an object
  is reflecting or scattering.

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Scattering

• When sunlight strikes very small objects, the
  light itself is deflected forward, sideways, and
  backwards.
• Air molecules are more effective scatterers of
  short (blue) wavelengths than long (red)
  wavelengths.

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Reflection

• Reflection differs from scattering in that
  reflection sends more light backwards.

• The amount of radiation returning from a surface
  compared to the amount initially striking that
  surface represents the reflectivity of the
  surface, called albedo.

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Albedo
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Energy Balance

• The earth and its atmosphere combined send off to
  space just as much energy as they receive.