Boundary Layer Climatology ATMOSGEOG 622'01

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Boundary Layer ClimatologyATMOS/GEOG 622.01

• Ground Thermal Variations

GEOG 622.02 measurements at OSU Airport, Nov, 2005
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Ground Temperatures Variations

• exponential decrease of diurnal wave amplitude
  (A) with depth
• phase shift of wave with depth
• For typical soil, A becomes insignificant below 1
  m.

Source The Hydrology Technical Group, Pacific
Northwest National Laboratory (PNNL), Richland,
Washington
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Thermal waves

• Pperiod
• t-tm time from time when T average
• Damping depth -z/d

• T Tm As exp(-z/d)sin(2p/P)(t-tm)-z/d
• T Tm As exp(-z/d)sin(2pti)-z/d
• where ti t/P

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Soil Physical Properties

• Porosity (fraction of air volume to total)
• Liquid water content (fraction of water volume to
  total)
• Chemical composition (i.e., mineral properties,
  fraction of various constituents)
• Biomass (roots, insects, bacteria, dead organic
  matter)
• Density (mass per volume, kg m-3)
• Thermal diffusivity (conduction rate)
• Heat capacity specific heat thermal
  diffusivity density

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Conductive heat transfer and soil properties

• Primarily by conduction, i.e. no convection
• Found to be proportional to temperature gradient
  and thermal conductivity (k).
• Thermal diffusivity (ah)
• ah k/C k/rc
• C heat capacity
• c specific heat
• r density
• See Table 4.1 (Arya, 2001)

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A Wave Equation

• T(t)O A sin(P/2p)
• IDL example plotted

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Thermal Wave Propagation in Subsurface

• From Fouriers equation of heat conduction
• Ts Tm As sin(2p/P)(t-tm)
• where Tm mean temperature at some depth
• As amplitude at the surface
• P period
• tm time when Ts Tm
• As the surface temperature is rising

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Wave Amplitude

• A Asexp(-z/d)
• Damping depth (d) is depth at which A is
  reduced by 1/e (e-folding depth)
• d (Pah/p)1/2
• If P 1 day 86400 s
• If ah thermal diffusivity of dry sand
• d0.081m
• If ah thermal diffusivity of wet sand
• d0.143 m

e 2.718281828459045235360287471352662
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Wave Phase Lag

• Phase lag z/d
• Complete reversal of wave at zpd
• The time lag from max and min in T zP/2pd

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Heat Storage (DHS) and Ground Heat Flux (HG)

• Heat storage (DHS) is significant, given time lag
  of wave.
• DHS increases in significance at times when HG
  fluctuations are greatest, i.e. at sunrise and
  sunset

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Evaluating Soil Thermal Conductivity
Temperature sensors -0.04 m -0.12 m -0.20 m 2
Heat Flux Plates at -0.08 m
Go Buckeyes!
GEOG 622.02 measurements at OSU Airport, Nov, 2005
If we know the heat flux (W m-2) from the heat
flux plates, we can solve for the thermal
conductivity, given
The soil pit
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TA,z1 0.38 m TG,z1 -0.02 m TG,z2 -0.08
m TG,z3 -0.16 m TG,z4 -0.32 m
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Measurement of HG

• Desire opaque sub medium
• difficult to measure in shallowest few cm
• difficult not to disturb the soil and thus change
  its conductive properties
• Measuring Tsoil profile near surface
• Must derive as, r, c, to get k or know k somehow
• Heat Flux Plate
• Simplifies above but disturbance problem persists
• Heat storage (DHS) is significant, given time lag
  of wave.

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How important is HG?

• HG tends to be the smallest term in the surface
  energy balance.
• HG is often neglected because over the course of
  1 day, it can average to zero.
• However, no term in SEB is too small to
  neglect. O. Pershan NOAA CMDL

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Applications for HG

• predicting frost conditions
• determining rate of heat storage/release of
  surface
• study of vegetation root zone
• environmental design of sub-surface structures
• determination of frost-depth
• evaluating climate change
• SEB