Data from Virtual Tall Towers

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Data from Virtual Tall TowersWhats Coming
Next

• David Tyndall
• Penn State Dept. of Meteorology
• ChEAS 2007

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• Talk Outline
• overview of virtual tall tower (VTT) methodology
• results from a few well-chosen sites
• future uses
• where this guy fits into the grander picture

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The VTT Method

• objective make an adjustment to near- surface
  observations (30m) to get an estimate of
  mid-CBL CO2
• note CBL -- BL must be convective!
• follows theory of Wyngaard Brost (1984)

assume
the vertical flux profile is linear
then
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The VTT Method

• assume that there are contributions from
  surface flux (bottom-up) and entrainment flux
  (top down)
• pertinent parameters scalar surface flux,
  w ( f heat flux, ABL height, T), h
• via dimensional analysis

b
t
h1 ABL height cws vert flux _at_ surface cw1
vert flux _at_ ABL top

• summing top-down and bottom-up contributions

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The VTT Method

• assume cwtop (entrainment flux) constant
  cwbottom (surface flux)
• gb gt evalutated at WLEF
• ABL top found using empirical relation from Yi
  et al. (2001) (ABL height from daily
• integrated surface heat flux)
• application of VTT method requires accurate
  precise measure of CO2, as well as CO2 flux,
  ABL height, w

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VTT in Practice

• shakedown at WLEF applied VTT method to obs
  taken at 30 m to predict 396 m CO2

WINTER
CORRECTIONS
RESIDUALS
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VTT in Practice

• shakedown at WLEF applied VTT method to obs
  taken at 30 m to predict 396 m CO2

SPRING
CORRECTIONS
RESIDUALS
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VTT in Practice

• shakedown at WLEF applied VTT method to obs
  taken at 30 m to predict 396 m CO2

SUMMER
CORRECTIONS
RESIDUALS
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VTT in Practice

• shakedown at WLEF applied VTT method to obs
  taken at 30 m to predict 396 m CO2

FALL
CORRECTIONS
RESIDUALS
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VTT in Practice

• WLEF (1997 2003), obs 14m above canopy

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VTT in Practice

• Harvard Forest (1993 2004), obs 24m above canopy

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VTT in Practice

• NOBS (1994 2004), obs 17m above canopy

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VTT in Practice

• Hegyhatsal (2002 2005), obs 72m above canopy

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VTT Future Work

• other testbeds for VTT method?
• locations where low-level and upper-level CO2,
  flux, met obs are available
• Cabauw other tall towers?
• aircraft profiles?
• provide as data product
• for use as another
• constraint in inversions
• application to Ring II and
• other friendly inversions

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Final Word where this guy fits in

• Meteo PhD candidate
• initially moved toward BL transport issues
• now moving toward BL-surface layer heterogeneity
  interaction/dynamics and LES modelling

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What are the values of gb gt?

• evalutated at WLEF tall tower using CO2 obs at
  11 m, 30 m, 76 m, 122 m, 244 m, 396 m
• best-fit functions found

Wang et al., in preparation
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What is the CBL height?

• CBL height found using Yi et al. (2001)
• empirical relationship developed using obs at
  WLEF
• ABL height a bG
• a 97.1 m
• b 25.5 m1/2/K1/2

Yi et al. 2001
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Corrections to Low-Level CO2 Measurements
Correction (ppm)
blue Harvard Forestred - WLEFgreen -
NOBSblue-green - Hegyhatsalblack - ARM-SGP
Year
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blue Harvard Forestred - WLEFgreen -
NOBSblue-green - Hegyhatsalblack - ARM-SGP
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Does it work at WLEF?
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Does it work elsewhere?
Harvard Forest Corrections (1994 - 2004)
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Harvard Forest Corrected Mid-CBL CO2 (1994 -
2004)
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