[Wrf-users] WRF Seasonal Variations

[Hahmann, Andrea N.]

This is only true if using WRF V3.3.   And always check your output to make sure that the important variables (I.e. Albedo, surface roughness, etc) are being changed and used in the simulations.  In previous versions, the output field Z0 (background surface roughness length) changes with time, but this field was not actually used in the model calculations, ZNT was actually the field being used and it had only two values, one for summer and one for winter.

Andrea
----
Andrea N. Hahmann
Senior Scientist
Wind Energy Division
Risø DTU

Technical University of Denmark
Risø National Laboratory for Sustainable Energy
Frederikborgvej 399, P.O. Box 49
4000 Roskilde, Denmark

Direct +45 4677 5471
Mobil: +45 2133 0550
ahah at risoe.dtu.dk
http://www.risoe.dtu.dk

From: Kevin Matthew Nuss <wrf at nusculus.com<mailto:wrf at nusculus.com>>
Date: Fri, 2 Sep 2011 20:21:40 +0200
To: "Huber, David" <dbh409 at ku.edu<mailto:dbh409 at ku.edu>>
Cc: "wrf-users at ucar.edu<mailto:wrf-users at ucar.edu>" <wrf-users at ucar.edu<mailto:wrf-users at ucar.edu>>
Subject: Re: [Wrf-users] WRF Seasonal Variations

Hi David,

No, the VEGPARM.TBL parameters get changed frequently (daily I believe or perhaps with every timestep). The VEGPARM.TBL values represent a range and get adjust within that range corresponding to the range of values the grid cell gets from the greenfrac database within WPS, which populates the GREENFRAC variable with average monthly values. During a run, WRF interpolates between the 12 monthly values for the current day. But to cause the updates to happen, you need to use the "sst_update" option in namelist.input. I believe most of the parameters go up with the exception of albedo, which goes from max to min as less soil is exposed when greenfrac goes from min to max. Also, there is a "usemonalb" variable in the namelist.input file which you might consider using (I don't).

If you turn on "sst_update" you have to re-run real.exe to produce another input file for wrf.exe. Read the WRF Users Guide about configuring for the new input files when "sst_update" is used.

Hmm. That was not explained well, but I hope you get the drift of what I was trying to say. And there is a little more in the User Guide.

Kevin


On Thu, Sep 1, 2011 at 4:22 PM, Huber, David <dbh409 at ku.edu<mailto:dbh409 at ku.edu>> wrote:
Hello,

If I were to perform a 1-year long simulation in WRF, would how often would it change the land cover parameters?  I noticed in VEGPARM.TBL that there are only winter and summer values, so does this mean that there is a sudden change in vegetation parameters once or possibly twice in a year-long simulation, that the vegetation parameters change regularly throughout the simulation, or that they stay the same as the initial vegetation parameters?

Thanks,

David

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