[Wrf-users] terrain features in 850mbar geopotential height

[Hein Zelle]

Dear WRF users,

we're seeing an unexpected terrain-following behaviour in the
geopotential height field at 850 mbar in our WRF output.  In the mean
time I'm convinced that I'm computing things correctly, so perhaps
there's a more conceptual problem.  We are computing

1)  the model level at which P+PB = 85000 Pa   (interpolated)
2)  the geopotential height (PH + PHB)/9.81  interpolated to that level.

Please see http://www.icce.rug.nl/~hein/geopotential_terrain.png for
an image over western europe, clearly showing the alps and other
terrain features in this field.  The variable shown is geopotential
height in m at 850 mbar level.  At 500mbar the terrain features are
mostly gone.  I've checked for earlier mails on this topic and found
one, but that poster claimed the problem went away after the first
time steps.  Not so in our case - this behaviour is consistent across
a 48 hour run.  We have also tried WRF POST, it shows the same
terrain-following behaviour and does the same computation as far as I
can see from the source code.

Are we computing the correct variable?  Charts from
www.wetterzentrale.de show the 850 mbar geopotential height field even
above the alps, suggesting they are computing a virtual field.  How
should we compute this from WRF output files?

Kind regards,

     Hein Zelle

-- 

  dr. ir. Hein Zelle

  Project manager

  ARGOSS: Atmospheric, marine & coastal information, systems and consultancy.

  ARGOSS BV
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  8325ZH Vollenhove
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----- End forwarded message -----


-- 

  dr. ir. Hein Zelle

  Project manager

  ARGOSS: Atmospheric, marine & coastal information, systems and consultancy.

  ARGOSS BV
  PO Box 61
  8325ZH Vollenhove
  The Netherlands
  Tel +31 (0)527242299
  Fax +31 (0)527242016
  Web  http://www.argoss.nl/


  Confidentiality Notice & Disclaimer

  This message and its attachments can contain confidential and/or
  proprietary information which could be subject to legal privilege or
  immunity. Unless you are a named addressee or receive this email on
  behalf of a named addressee you may not use, copy or disclose the
  contents in any manner. Should you receive this message in error, you
  are kindly requested to inform the sender and to delete all electronic
  or paper copies. ARGOSS BV does not accept any liability for any
  errors or omissions in the context of this email or its attachments
  which arise as a result of Internet transmission, nor accept liability
  for statements which are those of the author and not clearly made on
  behalf of ARGOSS.