Robin Hogan

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Observations of boundary-layer turbulence using
Doppler lidar and surface fluxes

• Robin Hogan
• Department of Meteorology
• University of Reading

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Daytime surface energy budget
Longwave
Shortwave
Warm, moist surface
Latent heat flux loss of energy by evaporation
Sensible heat flux heat transported to air by
turbulence and convection
Net radiation
Ground heat flux

• Updrafts (wgt0) tend to be warmer (Tgt0) and
  moister (qgt0) than average
• Downdrafts (wlt0) tend to be cooler (Tlt0) and
  dryer (qlt0) than average
• Hence the temperature flux ( ) and water
  vapour flux ( ) are both positive in the
  day
• They can be measured with fast-response w, T and
  q.

Height
Temperature or mixing ratio
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Fluxes on 11 July 2007
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Skewness in convective BLs

• Both model simulations and laboratory
  visualisation show convective boundary layers
  heated from below to have narrow, intense
  updrafts and weak, broad downdrafts, i.e.
  positive skewness

Narrow fast updrafts
Wide slow downdrafts
Courtesy Peter Sullivan NCAR
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Conclusions

• Potential for lots of new boundary-layer science
  to be done with such instruments
• Possible applications
• Evaluation of boundary-layer schemes, e.g. Met
  Office scheme (Adrian Lock) which predicts the
  depth to which surface- and cloud-top-driven
  turbulence will penetrate can infer directly
  from skewness
• Test the inferences of turbulence intensity using
  tethered balloon
• Study turbulence in the poorly understood and
  poorly modelled nocturnal boundary layer
• Combine Doppler lidar with RAMAN humidity to get
  profiles of latent heat flux
• Potential for Chilbolton to become a FLUXNET
  site with its CO2 measurements?

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