Energy Budgets of Ohio Grass in Autumn

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Energy Budgets of Ohio Grass in Autumn
Boundary Layer Climatology
ATMOS/GEOG 622.01
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Site Setup
Site Ohio State University Airport Duration
November 3-12, 2005 Flux Region
0.4-3.24m Instrumentation - 3 Fine Wire
Thermocouples - 2 CS HMP45C Temperature and
Humidity probes - 3 Met-One 014A Wind Speed
Sensors - Kipp Zonen CNR1 Net Radiometer
- CS HFT3 Heat Flux Plate Data Recording
- CS CR1000 Data Logger - 10 minute averaged
data
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Radiation Components
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Sensible Heat Flux
Review

• A direct flux in W m-2
• It is directly related to temperature differences
  between the surface and the adjacent atmosphere.
• Usually negative (away from the surface) during
  the day
• Temperatures at the surface are higher than air
  aloft
• Usually positive (toward the surface) at night
• Temperatures at the surface are cooler than air
  aloft
• General timing is not always the case.
• Flux follows the temperature gradient
• Energy flows from higher concentrations to lower
  concentrations

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Sign Convention in this Study

• Sign convention used with respect to the surface
  plane.
• Positive fluxes are those which move toward the
  surface plane.
• Negative fluxes are those which move away from
  the surface plane.

P 13
(Arya 2001)
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Sensible Heat Flux
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Latent Heat Flux
Review

• An indirect flux in W m-2
• A function of the latent energy associated with
  phase changes of H2O, i.e., evaporation and
  condensation
• Negative (away from the surface, toward the
  atmosphere) whenever evaporation or transpiration
  is occurring at the surface
• Evapo-transpiration cools the surface
• Occurring most often during daytime
• Positive (heating the surface) whenever
  condensation is occurring
• Occurs most often during the early morning as dew
  forms
• Occurs during precipitation

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Latent Heat Flux
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Cumulative Evaporation
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• Evaporation process fueled by solar irradiance
• during the day, QE reaches its most negative
  value when downward shortwave radiation is
  greatest
• at night, QE reaches its most positive value when
  downward shortwave radiation is zero

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Ground Heat Flux W m-2

• Due to the conduction of energy up and downward
  in the ground
• Thermal conductivity is a function of at least 7
  soil properties
• Usually negative (away from the surface interface
  and into the ground) during the daytime
• Surface air-ground interface is warmer than the
  soil beneath
• Usually positive (toward the surface plane from
  the ground) during the nighttime
• Surface air-ground interface is cooler than the
  soil beneath
• Opposite conditions are possible
• Surface may be warmed by another feature
• E.g. warm air mass at night (H)
• E.g. strong downward longwave radiation from
  nighttime clouds (RL?)
• What else can warm the surface?

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All Energy Budget Components
net radiation (black), sensible heat flux (red),
latent heat flux (blue), and ground heat flux
(green).
Changes in one component means changes in another.
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(No Transcript)
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Comparison of Heat Storage with Residual Energy
D. Steinhoff
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Frontal Situations
November 6, 2005
November 7, 2005
Surface Weather Maps and Station Weather 700 EST
(NOAA/NCEP)
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Frontal Situations
November 10, 2005
November 9, 2005
Surface Weather Maps and Station Weather 700 EST
(NOAA/NCEP)
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Effect of Fronts on the Microclimate
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Effect of Fronts on the Microclimate
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Effect of Fronts on the Microclimate
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Fronts in the Data
Average Temperature C
Average Pressure hPa
Range of Wind Speed kts
Precip in
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Component Changes
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Warm Fronts

• - Stability shifts from stable to unstable (both
  close to neutral)
• Sensible heat flux switches to negative (normal
  for time of day)
• Latent heat flux becomes more negative (normal
  for time of day)
• Ground heat flux becomes more negative
  (unusually early)

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Cold Fronts

• - Stability becomes slightly more stable
• Sensible heat flux changes are different
• Latent heat flux becomes less negative (normal
  for the 6th)
• Ground heat flux becomes more positive
  (unusually large values)

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Main Conclusions of OSU Airport Energy Budget
Experiment

• The effects of frontal passages on energy budget
  components are clearly observed in changes in
  daily mean values.
• At this time of year, H heats the surface, on
  average, except when cold air masses invade
• Net evaporation loss is evident in the
  measurements
• Net solar irradiance is the driver for
  evaporation
• Most of the residual in energy budget closure can
  be explained by changes in ground stored heat
  energy.