# [ncl-talk] geopotential height calculation

Zhifeng Yang yangzf01 at gmail.com
Fri Oct 26 09:27:53 MDT 2018

```Hi Laura,
the MPAS 6.0 user guide. There is a statement in page 63 about the vertical
coordinates. It says like
------------------------------------------------------------------------------------------------------------
The vertical coordinate in MPAS-Atmosphere is ζ and has units of length,
where 0 ≤ ζ ≤ z t and z t is the
height of the model top. The relationship between the vertical coordinate
and height in the physical domain
is given as
z = ζ + A h s (x, y, ζ)                                (C.1)
where (x, y) denotes a location on the horizontal mesh and ζ is the
vertical coordinate (ζ is directed radially
outward from the surface of the sphere, or perpendicular to the horizontal
(x, y) plane in a Cartesian
coordinate MPAS-A configuration).
---------------------------------------------------------------------------------------------------------

Best,
Zhifeng

On Thu, Oct 25, 2018 at 11:24 AM Laura Fowler <laura at ucar.edu> wrote:

> Hi Barry:
> I am always kind of cautious using "model-specific" functions like the WRF
> suite functions for an other model, especially when the vertical coordinate
> system is different. I have not looked at differences in using wrf
> functions versus generic functions for vertical interpolation so I cannot
> really give you a definitive answer. May be it works just fine.
>
> Cheers,
> Laura
>
>
> On Wed, Oct 24, 2018 at 8:49 AM Barry Lynn <barry.h.lynn at gmail.com> wrote:
>
>> Laura:
>>
>> There are many wrf_ncl functions I use (plus get user variables).
>>
>> Is it possible with MPAS to use similar functions?
>>
>> Barry
>>
>> On Wed, Oct 24, 2018 at 5:25 PM Laura Fowler <laura at ucar.edu> wrote:
>>
>>> Zhifeng:
>>>
>>> I just read your ncl question related to the calculation of the 500 hPa
>>> geopotential height in MPAS. Just wanted to let you know that the vertical
>>> discretization uses a height coordinate and not sigma (see Klemp (2011) for
>>> details on the terrain-following coordinate system used in MPAS).
>>>
>>> To calculate the 500 hPa geopotential height, you need to use the
>>> "height" variable zgrid that is written in the init condition file by
>>> default if you have not saved it in a history file. You also need the
>>> "pressure" variable which you need to save in your history file. Once you
>>> have those 2 fields from your outputs, you can use any of the ncl functions
>>> int2p, int2p_n, or int2p_n_Wrap to interpolate you data to the 500 hPa
>>> level.
>>>
>>> Note that MPAS also calculates the geopotential height at several fixed
>>> pressure levels too (see the User's guide on how to use the "diagnostics"
>>> stream so that you do not have to do that separately.
>>>
>>>
>>> Hope this helps,
>>> Laura
>>>
>>>
>>> On Tue, Oct 23, 2018 at 3:13 PM Zhifeng Yang <yangzf01 at gmail.com> wrote:
>>>
>>>>
>>>> Sorry for less information. The vertical grid in MPAS is sigma. The
>>>> horizontal grid is Voronoi mesh, unstructured grid. I saw there is a
>>>> section in NCL processing MPAS model data. I thought MPAS is very common
>>>> while using NCL. Here I attached the output from ncdump and
>>>> printVarSummary. There are three types of model output files. diagnos,
>>>> history, and restart. I am planning to use history output to calculate the
>>>> geopotential height.
>>>>
>>>> I took a look of several wrf related functions in NCL, e.g.
>>>> wrf_interp_3d_z, wrf_interp_2d_xy. However, they are for latitude-longitude
>>>> grids, like WRF.
>>>>
>>>> Zhifeng
>>>>
>>>>
>>>> On Mon, Oct 22, 2018 at 11:02 PM Barry Lynn <barry.h.lynn at gmail.com>
>>>> wrote:
>>>>
>>>>> Just curious -- have your tried the WRF functions?
>>>>>
>>>>> On Mon, Oct 22, 2018 at 11:53 PM Adam Phillips <asphilli at ucar.edu>
>>>>> wrote:
>>>>>
>>>>>> Hi Zhifeng,
>>>>>> question. Is your data on hybrid-sigma levels, or some other vertical
>>>>>> coordinate? Is your data on an unstructured grid, or some other type? A
>>>>>>
>>>>>> On Mon, Oct 22, 2018 at 1:40 PM Zhifeng Yang <yangzf01 at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Hi all,
>>>>>>>
>>>>>>> I want to get the geopotential height at 500 mb from MPAS model
>>>>>>> output. Do we have NCL function to calculate it, or other possible methods?
>>>>>>> Thank you
>>>>>>>
>>>>>>> Zhifeng
>>>>>>> _______________________________________________
>>>>>>> ncl-talk mailing list
>>>>>>> ncl-talk at ucar.edu
>>>>>>> List instructions, subscriber options, unsubscribe:
>>>>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR
>>>>>> www.cgd.ucar.edu/staff/asphilli/   303-497-1726
>>>>>>
>>>>>> <http://www.cgd.ucar.edu/staff/asphilli>
>>>>>> _______________________________________________
>>>>>> ncl-talk mailing list
>>>>>> ncl-talk at ucar.edu
>>>>>> List instructions, subscriber options, unsubscribe:
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>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Barry H. Lynn, Ph.D
>>>>> Senior Associate Scientist, Lecturer,
>>>>> The Institute of the Earth Science,
>>>>> The Hebrew University of Jerusalem,
>>>>> Givat Ram, Jerusalem 91904, Israel
>>>>> Tel: 972 547 231 170
>>>>> Fax: (972)-25662581
>>>>>
>>>>> C.E.O, Weather It Is, LTD
>>>>> Weather and Climate Focus
>>>>> http://weather-it-is.com
>>>>> Jerusalem, Israel
>>>>> Local: 02 930 9525
>>>>> Cell: 054 7 231 170
>>>>> Int-IS: x972 2 930 9525
>>>>>
>>>>> _______________________________________________
>>>> ncl-talk mailing list
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>>>>
>>>
>>>
>>> --
>>>
>>> !-------------------------------------------------------------------------------------------------------------
>>> Laura D. Fowler
>>>
>>> Mesoscale and Microscale Meteorology Division (MMM)
>>> National Center for Atmospheric Research
>>> P.O. Box 3000, Boulder CO 80307-3000
>>>
>>> e-mail: laura at ucar.edu
>>> phone: 303-497-1628
>>>
>>>
>>> !-------------------------------------------------------------------------------------------------------------
>>>
>>
>>
>> --
>> Barry H. Lynn, Ph.D
>> Senior Associate Scientist, Lecturer,
>> The Institute of the Earth Science,
>> The Hebrew University of Jerusalem,
>> Givat Ram, Jerusalem 91904, Israel
>> Tel: 972 547 231 170
>> Fax: (972)-25662581
>>
>> C.E.O, Weather It Is, LTD
>> Weather and Climate Focus
>> http://weather-it-is.com
>> Jerusalem, Israel
>> Local: 02 930 9525
>> Cell: 054 7 231 170
>> Int-IS: x972 2 930 9525
>>
>>
>
> --
>
> !-------------------------------------------------------------------------------------------------------------
> Laura D. Fowler
>
> Mesoscale and Microscale Meteorology Division (MMM)
> National Center for Atmospheric Research
> P.O. Box 3000, Boulder CO 80307-3000
>
> e-mail: laura at ucar.edu
> phone: 303-497-1628
>
>
> !-------------------------------------------------------------------------------------------------------------
>
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