Evaluation of HIRLAM sensible heat flux and using wind and temperature profiles

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Evaluation of HIRLAM sensible heat flux and using
wind and temperature profiles

• M.Sofiev (FMI), E.Genikhovich(MGO)

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Problem statement

• Key characteristics of the boundary layer -
  T,u,L,w - can be computed
• from temperature and wind profiles
• from sensible heat flux provided by NWP
• Two approaches do not always meet
• Way to cross-check is to re-state sensible heat
  flux from profile data and compare with the
  internal one

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Methodology

• An approach of Groisman Genikhovich (1997)
• Sensible heat flux H is a diagnostic variable of
  the method, which is based on eddy diffusivity KZ
  estimated from similarity theory

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Heat flux comparison

• Patterns over the whole 2000 were compared
• The sensible heat flux qualitative pattern is
  reproduced very well
• Quantitatively, there are large differences
• Downward flux (inversions) everywhere and upward
  flux (convective) over sea are much stronger in
  the re-stated H
• Upward (convective) flux over land is
  considerably smaller in the re-stated H
• Year-long mean strong downward shift of the
  re-stated flux over land, moderate-to-strong
  upward shift over oceans.

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Mean-2000 comparison
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Question

• How can the sensible heat flux re-stated from
  HIRLAM profiles be that different from HIRLAM-own
  internal variable?

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Possible reasons

• Methodology of the flux re-stating is based on
  similarity theory, i.e. is good for near-neutral
  conditions
• however, quantile chart shows same tendencies for
  near-neutral conditions too
• Latent heat flux is so far ignored
• HIRLAM may have sensible and latent fluxes
  partially compensating each other
• influence of latent heat flux may be enforced due
  to over-estimated low-level clouds and
  evaporation
• however, latent heat does not explain Saharas
  sensible flux gt400 Wm-2, while profiles suggest a
  factor of 4 smaller