What is temperature

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What is temperature

• A measure of the average kinetic energy (motion)
  of individual molecules in matter.

Low Temperature Slow molecular motion
High Temperature Fast molecular motion
we feel the effect of temperature as sensible
heat transfers from warmer bodies to cooler
bodies
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Lets experiment with crickets Crickets chirp
at a speed that depends on the air
temperature Crickets chirp faster with increasing
temperature and slower with decreasing
temperatures.
Field Cricket T 50 (N - 40 / 4)   Snowy
Tree Cricket T 50 (N - 92 / 4.7)   T is the
temperature and N is the number of chirps per
minute. The simplest method is to count the
number of chirps in 15 seconds and add 40. Lets
try it
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male Apr. 23 1999
male Aug. 17 1999
male Oct. 10 2000
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How does a thermometer work?

• Mercury or alcohol thermometers use the principle
  that fluid expands when heated
• fluid is sealed in a glass tube and rises when
  heated and falls when cooled
• mercury freezes at -38.2?F (-39?C) but alcohol
  freezes at -170?F (-112?C)
• for reference water freezes at 32?F (0?C)
• Thermistor measures temp. by sensing the
  electrical resistance of a semi-conducting
  material
• the resistance changes by 4 per ?C

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Principal Temperature Controls  

• Latitude  
• Affects insolation
• Altitude  
• High altitude has greater daily range
• High altitude has lower annual average
• Cloud Cover  
• High albedo
• Moderate temperatures cooler days, warmer nights

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Altitude

• Normal Lapse Rate 6.4 Co / 1000 m

Because the density of atmosphere decreases with
altitude making it less able to absorb and
radiate sensible heat Areas in mountains are
cooler on average and temp. ranges are greater
than areas at sea level Surfaces in the mountains
gain energy quicker and lose energy quicker than
lowlands
Insolation received is more intense because there
is less atmosphere
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LandWater Heating Differences 

• Land and water absorb and store energy
  differently
• Land heats and cools faster than water
• Moderate temperatures associated with water
  extreme temperatures with land

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This depends on several factors

• Evaporation
• Latent Heat - causes cooling
• More important over water (oceans)
• When water evaporates, heat energy is absorbed
  and stored in water vapor as latent heat (LE)
• Transparency
• Deeper light penetration

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Transparency - ground is opaque, water is
transparent Light hitting the ground is absorbed
and heats the ground surface but not very deep
Light hitting water penetrates to an average
depth of 60m (200ft) and heats the whole area
called the photic zone
Depth (m)
Land
Ocean
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• Oceans can absorb more heat than the land.
• Specific heat heat energy required to raise
  temperature 1 oC.
• Water has a higher specific heat than land
• Water can hold more heat and has a higher heat
  capacity
• Circulation
• Oceans have currents
• Resulting in mixing of cooler and warmer waters,
  spreading the energy over greater volume

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LandWater Heating Differences  
Figure 5.7
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summary (maritime vs. continentality)

• Evaporation causes cooling over water
• why you need a jacket to go out on the water
  even on a hot day
• Transparency or opacity causes heating of only
  the top layer of ground
• why caves remain a constant cool temperature
  year round
• why sand at the beach is dry and scalding on
  top, but cool and wet just underneath

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summary (maritime vs. continentality)

• Specific heat means water takes longer to heat or
  cool than land
• why temperatures near ocean are cooler during
  the day and warmer at night than inland
• Movement of water in general and in currents
  specifically redistributes heat
• why climate is moderate year round in
  midlatitudes on the western margins of oceans

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Mean temperature map for January Isotherm
connecting points with the same temperature by a
line (Just like a contour line on a topographic
map)
Heavy dashed line is the thermal equator
isotherm having the highest mean temperature
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Note that isotherms in general bend southward
over the continents and go back to nearly
straight lines over the oceans This is because
of the uneven heating of land vs. water that we
just talked about Cold air from the pole is
being pushed southward over the continent
Note also that isotherms bunch up northward in
mountainous areas in S hemisphere (Andes)
because of the effects of altitude lowering
temperatures
Air cools at higher altitudes temperatures
equivalent to lowlands much further S closer to
poles
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Thermal equator has shifted northward Isotherms
bend northward over continents now Bunching in
the mountains is still northward, because there
is still cooler air at higher altitudes
Many more isotherms much lower temperatures
over Antarctica in July, the time of 24 hours
darkness for that region
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Map showing annual temperature ranges Larger
ranges are predominantly located in the northern
hemisphere most of the Earth's land is in the N
hemisphere continentality dominates there
Also note the harsh conditions in Siberia with
ranges gt40?C or 70?F (see fig. 5.15 for more
information)
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Air Temperature and the Human Body

• The temperature we actually feel in the air is
  the Sensible Heat of the air.
• Called the apparent temperature
• Varies between individuals and cultures living in
  different parts of the world
• Air also has heat in the form of water vapor.
  This is Latent Heat.
• The temperature we feel depends on the water
  vapor content (humidity) and wind speed as well
  as the real air temperature

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Wind Chill

• The enhanced rate at which body heat is lost to
  the air, related to heat energy loss
• Formula to calculate this relationship developed
  in 1945, National Weather Service began reporting
  the wind chill in 1970
• When the wind is blowing it feels cooler than the
  actual temperature.
• Moving air transports heat away faster.
• Wind chill correlates cold and wind speed

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Wind Chill Table
shaded areas represent amount of time before
frostbite occurs
Figure 1
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Heat Index Apparent Temperature

• Human body's reaction to the combination of air
  temperature and water vapor (humidity)
• It feels hotter than the actual temperature when
  there is high humidity.
• High humidity ? high water vapor in air ?
  Perspiration does not evaporate.
• Heat index
• Correlates heat and humidity

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Heat Index Table
Figure 2