[Wrf-users] Confused about model height

[Eric Altshuler]

Hello Lynn,

The lowest model level is a surface of constant sigma (native hybrid terrain-following vertical coordinate) so near the ground, the height of model level surfaces will follow the surface topography. However, John was referring to the geopotential height on constant pressure surfaces, not on native model coordinate surfaces. The raw WRF history files (wrfout*) contain fields on native model coordinate surfaces, which is probably what you are looking at. But ARWpost vertically interpolates the WRF history output to constant pressure surfaces.

Best regards,

Eric L. Altshuler
Assistant Research Scientist
Center for Ocean-Land-Atmosphere Studies
4041 Powder Mill Road, Suite 302
Calverton, MD 20705-3106
USA

E-mail: ela at cola.iges.org
Phone: (301) 902-1257
Fax: (301) 595-9793

----- Original Message -----
From: sparling at umbc.edu
To: "Eric Altshuler" <ela at cola.iges.org>
Cc: "John Krasting" <krasting at envsci.rutgers.edu>, wrf-users at ucar.edu
Sent: Tuesday, March 10, 2009 10:54:01 PM GMT -05:00 US/Canada Eastern
Subject: Re: [Wrf-users] Confused about model height

Also,if you do a line plot of elevation vs lat (or lon) and overplot the
geopotential height of the lowest model level and you can see that it
follows the topography.
Cheers,

Lynn

> Hello John,
>
> Geopotential heights are always given as height above sea level (I think
> the definition is more rigorous than this, but the effects of the
> non-spherical earth and non-uniform gravitiational fields are second-order
> effects). Otherwise, if height fields were computed as the height above
> the ground level, height fields would be distorted by the pattern of
> surface topography, and could not be used for calculating geostrophic
> winds, for example.
>
> Best regards,
>
> Eric L. Altshuler
> Assistant Research Scientist
> Center for Ocean-Land-Atmosphere Studies
> 4041 Powder Mill Road, Suite 302
> Calverton, MD 20705-3106
> USA
>
> E-mail: ela at cola.iges.org
> Phone: (301) 902-1257
> Fax: (301) 595-9793
>
> ----- Original Message -----
> From: "John Krasting" <krasting at envsci.rutgers.edu>
> To: wrf-users at ucar.edu, "WRF Help" <wrfhelp at ucar.edu>
> Sent: Tuesday, March 10, 2009 3:01:14 PM GMT -05:00 US/Canada Eastern
> Subject: [Wrf-users] Confused about model height
>
> Hi Users -
>
> Just want to confirm exactly how height is calculated using ARWpost.
>
> Is this the height above ground level or above sea level?  I'm
> assuming that since WRF is using a terrain-following hydrostatic
> coordinate, that these values are above ground level.
>
>
> Thanks,
> John
>
> -----------------------------
>
> more module_calc_height.f90
> !! Diagnostics: Height
>
> MODULE module_calc_height
>
>   CONTAINS
>   SUBROUTINE calc_height(SCR, cname, cdesc, cunits)
>
>   USE constants_module
>   USE module_model_basics
>
>   !Arguments
>   real, pointer, dimension(:,:,:)       :: SCR
>   character (len=128)                   :: cname, cdesc, cunits
>
>
>   SCR      = ( (PH+PHB) / G ) / 1000.
>   cname    = "height"
>   cdesc    = "Model height"
>   cunits   = "KM"
>
>   END SUBROUTINE calc_height
>
> END MODULE module_calc_height
> _______________________________________________
> Wrf-users mailing list
> Wrf-users at ucar.edu
> http://mailman.ucar.edu/mailman/listinfo/wrf-users
> _______________________________________________
> Wrf-users mailing list
> Wrf-users at ucar.edu
> http://mailman.ucar.edu/mailman/listinfo/wrf-users
>
>



^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Lynn Sparling			sparling at umbc.edu
Associate Professor		PH:   410-455-6231
Department of Physics		FAX: 410-455-1072
University of Maryland, Baltimore County
1000 Hilltop Circle
Baltimore, MD 21250

"One can measure to test the ruler." -Wittgenstein