[Wrf-users] WRF height variables question

Fri Oct 13 00:32:52 MDT 2017

Hi Irina,

the WRF vertical grid is not at constant height above sea but is following the ground with eta levels based on pressure.
To compute altitude above sea, do as follow:  
z = (PH+PHB)/g  where g is 9.81 m/s2 
PH and PHB are the variables extracted from wrfout file 

see bellow extract from wrfout file :
ncdump -h wrfout... | grep PH
	float PH(Time, bottom_top_stag, south_north, west_east) ;
		PH:FieldType = 104 ;
		PH:MemoryOrder = "XYZ" ;
		PH:description = "perturbation geopotential" ;
		PH:units = "m2 s-2" ;
		PH:stagger = "Z" ;
		PH:coordinates = "XLONG XLAT XTIME" ;
	float PHB(Time, bottom_top_stag, south_north, west_east) ;
		PHB:FieldType = 104 ;
		PHB:MemoryOrder = "XYZ" ;
		PHB:description = "base-state geopotential" ;
		PHB:units = "m2 s-2" ;
		PHB:stagger = "Z" ;
		PHB:coordinates = "XLONG XLAT XTIME" ;

To extract values at a given altitude, you will have the compute the eta levels altitude at each grid position in i,j,eta then to interpolate your variable at the wanted altitude.

Best regards
Thierry

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De : Wrf-users [mailto:wrf-users-bounces at ucar.edu] De la part de wrf-users-request at ucar.edu
Envoyé : jeudi 12 octobre 2017 20:00
À : wrf-users at ucar.edu
Objet : Wrf-users Digest, Vol 158, Issue 8

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Today's Topics:

   1. Is this warning in WPS 3.8.1 important? (Douglas Lowe)
   2. WRF height variables question (Irina Rypina)

----------------------------------------------------------------------

Message: 1
Date: Thu, 12 Oct 2017 10:42:38 +0000
From: Douglas Lowe <Douglas.Lowe at manchester.ac.uk>
To: "wrf-users at ucar.edu" <wrf-users at ucar.edu>
Subject: [Wrf-users] Is this warning in WPS 3.8.1 important?
Message-ID:
	<43E6B083008E774B87C4283E0FFA4E700170136382 at MBXP02.ds.man.ac.uk>
Content-Type: text/plain; charset="us-ascii"

Dear all,

While running WPS 3.8.1 using ECMWF meteorology I get this warning message:
WARNING: Entry in METGRID.TBL not found for field ST100255. Default options will be used for this field!
WARNING: Entry in METGRID.TBL not found for field SM100255. Default options will be used for this field!

Comparing the METGRID.TBL for 3.8.1 with that for 3.4.1 I find that the entry for ST100255 has been replaced by an entry for ST100289 (same for SM100255).
<         fill_lev = 289 : ST100289(200100)
---
>         fill_lev = 255 : ST100255(200100)

However my met_grid files have only the ST100255 variable, and no ST100289 variable.
Which is because the Vtable (which I'd copied from my original 3.4.1 setup) has ST100255 not ST100289.

Comparing the default Vtables for 3.4.1 and 3.8.1 I find that ST100289 is essentially ST100255, just with a different variable name. And looking in Registry.EM_COMMON for v3.8.1 I can find an entry for ST100255, but not one for ST100289 - so WRF would not actually be aware of this variable if I were to use it.

So, I guess what I need to do is modify METGRID.TBL to use ST100255 again (instead of ST100289). However, I'd like to also ask 

Why was WPS modified to use the ST100289 variable, but WRF hasn't? Was this in preparation for a change which has now been made in WRF 3.9.1? Should I modify METGRID.TBL to use ST100255 again (instead of ST100289), or would a better solution be to back-port some code from v3.9.1 which uses ST100289 to my version of v3.8.1 (I'm not going to move up to 3.9.1 yet, because we've too many local changes to the code to move versions every year)?

Thanks,
Doug

------------------------------

Message: 2
Date: Wed, 11 Oct 2017 17:57:22 -0400
From: Irina Rypina <irypina at whoi.edu>
To: wrf-users at ucar.edu, WRF Help <wrfhelp at ucar.edu>
Subject: [Wrf-users] WRF height variables question
Message-ID:
	<20171011175722.Horde.hfMoRUv4Cn9Z3pPCPYpHc2A at webmail.whoi.edu>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed; DelSp=Yes

Hi,

I am trying to use WRF output (from a wrfout* file) and have a question about WRF variables.

For my analysis, I only need to know the 3 components of air velocities, u,v and w, and their corresponding grids in 3d (lat, lon, height above sea level) and time.

I believe "U", "V", and "W" variables in WRF give the 3 components of velocity, and I think the lateral lat and long grids for these are given by "XLONG_U,XLATG_U", "XLONG_V,XLATG_V", and "XLONG,XLATG."

I also found the time variable "XTIME" that gives time stamps for "U", "V", and "W."

But what I cannot find are the z-grids (height above sea level in
meters) at which "U", "V", and "W" are given.

Can anyone please help me with this?

Thanks!
Irina

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