Net Radiation and Surface Temperature

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Net Radiation and Surface Temperature
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Surface Energy Fluxes and Temperature

• When the surface absorbs more energy than it
  loses, then the temperature of the surface
  increases.
• When the surface loses more energy than it gains,
  then the temperature of the surface decreases.

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Net Radiation

• The net radiation is the difference between the
  radiant energy absorbed and the radiant energy
  emitted.

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Net Radiation (Cont.)

• Net radiation solar radiation absorbed
• terrestrial radiation absorbed
• - terrestrial radiation emitted

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Net Radiation Example

• If the solar radiation absorbed by the Earths
  surface is 600 W/m2, the terrestrial radiation
  absorbed is 80 W/m2, and the terrestrial
  radiation emitted by the Earths surface is 300
  W/m2, then what is the net radiation at the
  surface?

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Net Radiation Example (Cont.)

• Net Radiation 600 W/m2
• 80 W/m2
• - 300 W/m2
• __________
• Net Radiation 380 W/m2

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Net Radiation Example (Cont.)
From atmosphere
From surface
From sun
300 W/m2
600 W/m2
80 W/m2
Net Radiation 380 W/m2 at surface
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Daily Cycles of Net Radiation and Temperature

• The daily cycle of net radiation is the primary
  factor that determines the normal daily cycle of
  temperature.
• When the net radiation is positive, the
  temperature usually increases and when the net
  radiation is negative the temperature usually
  decreases.

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At night the terrestrial radiation emitted by the
surface exceeds the terrestrial radiation emitted
to the surface by the atmosphere and the
temperature decreases.
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Around sunrise some solar radiation starts to
reach the surface and the net radiation starts to
increase. However, the net radiation is still
negative and so the temperature continues to
decrease.
Sunrise
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At some point after sunrise enough solar
radiation reaches the ground that the net
radiation becomes zero. This is the time when
the minimum temperature occurs.
Net Rad. is zero
Minimum Temp.
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As the sun moves higher in the sky increasing
solar radiation reaches the surface, the net
radiation becomes positive and the temperature
increases.
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Solar radiation peaks at noon Local Solar Time
when the sun is at its highest point in the sky.
This is also the time when the net radiation is
at a maximum.
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After noon the sun starts to move lower in the
sky and the net radiation starts to decrease.
However, as long as the net radiation remains
positive, the temperature will continue to
increase.
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Eventually, as the sun gets lower in the sky the
net radiation will again be zero. At this point
the temperature stop increasing and the maximum
temperature occurs
Net rad. is zero
Maximum Temp.
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Once the net radiation goes negative again, then
the temperature starts to decrease.
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The Annual Cycle of Net Radiation

• The annual cycle of net radiation plays a large
  role in the determination of the observed pattern
  of temperatures.
• In the tropics the net radiation is positive
  throughout the year producing warm temperatures
  during all months.

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The Annual Cycle of Net Radiation (Cont.)

• In the middle latitudes the net radiation is
  negative in winter and positive in summer. This
  produces a pattern of cold winters and warm
  summers.
• In the polar regions the net radiation is
  negative throughout the year. This produces the
  cold temperatures we associated with polar
  regions.

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Other Processes That Affect Temperatures at the
Surface

• Latent energy transfers affect the surface
  temperature. It takes energy to evaporate water
  and melt snow. Energy that is absorbed during
  phase changes of water is not available to
  increase the surface temperature.

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Other Processes That Affect Temperatures at the
Surface (Cont.)

• When a lot of energy is absorbed during the
  evaporation of water from a moist surface, the
  temperature will not increase as much.

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Other Processes That Affect Temperatures at the
Surface (Cont.)

• When air passes over a surface with a different
  temperature, there is a transfer of internal
  energy between the warmer and colder molecules.
• When the air is cooler than the surface, internal
  energy is transferred from the surface to the air
  and the air temperature increases.

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Other Processes That Affect Temperatures at the
Surface (Cont.)

• When the air is warmer than the surface, then
  internal energy is transferred from the air to
  the surface and the air temperature decreases.

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Other Processes That Affect Temperatures at the
Surface (Cont.)

• The movement of large air masses and front can
  affect the temperature of the air at the surface.
  
• Proximity to a body of water can affect the
  temperature if the wind blows across the water
  before reaching land.

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Land and Water Contrasts

• Specific heat (energy) is the amount of energy to
  raise the temperature of one kilogram of a
  substance by one degree Celsius.

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Land and Water Contrasts (Cont.)

• The specific heat of water is about five times
  greater than the specific heat of a typical land
  surface.
• Thus, it takes a transfer of approximately five
  times as much energy to change the temperature of
  water than it does to change the temperature of
  land by the same number of degrees.

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Land and Water Contrasts (Cont.)

• The result is that land warms up more quickly in
  spring and cools off more quickly in the autumn.

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Lake Erie is usually colder than the land during
the spring and summer. When the winds blows from
the lake toward the land, it brings in air with a
lower temperature.
Cool Lake
Cool lake breeze
Warmer inland
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In the autumn the land cools off faster than Lake
Erie. So the temperatures are higher over the
lake than over the surrounding land. When the
wind blows from the lake toward the land it
brings air with a higher temperature.
Warmer Lake
Warm lake breeze
Cooler inland
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Land and Water Contrasts

• Thus, the effect of a body of water is to
  moderate the temperatures by making them cooler
  in spring and summer, and warmer in autumn and
  winter.
• Areas near the oceans or other large bodies of
  water tend to have milder temperatures than
  places further inland.

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Temperature Ranges

• The temperature range is the difference between
  the maximum and minimum temperature.
• The annual temperature range is the difference
  between the temperature of the warmest month and
  the coldest month.

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Fargo
Seattle
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Annual Temperature Ranges

• Fargo, North Dakota (47N, 97W, 273m)
• J F M A M J J A S O
  N D
• (TF) 7 11 25 42 55 65 71 69 59 46 23 13
• Annual Range 71F - 7F 64F

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Annual Temperature Ranges (Cont.)

• Seattle, WA (47.5N, 122.5W, 118 m)
• J F M A M J J A S O N
  D
• (TF) 38 41 44 49 56 60 65 64 60 52 44 41
• Annual range 65F - 38 27F

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Eureka
Columbus
Phoenix
Miami
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Annual Temperature Range (Cont.)

• The annual temperature range is much greater for
  inland locations than it is for places closer to
  the oceans.

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Boston
Seattle
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East Vs. West Coast

• The annual temperature range in the the middle
  latitudes is greater on the east coast of the
  U.S. than it is on the west coast, because the
  prevailing wind direction is from the west.

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Atlantic Main Development Region (MDR) (10-25N,
30-60W)
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Monthly Sea Surface Temperatures (SSTs)

• The maximum and minimum Sea Surface Temperatures
  (SSTs) usually occur a month or two after they do
  on land.