[ncl-talk] geopotential height calculation

[Laura Fowler]

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:

> Hi Adam and Barry,
>
> 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,
>>> I think more information is needed about your data to answer the
>>> 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
>>> printVarSummary of your data would also be helpful.
>>> Adam
>>>
>>> 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
>>>> _______________________________________________
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>>>
>>>
>>> --
>>> Adam Phillips
>>> Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR
>>> www.cgd.ucar.edu/staff/asphilli/   303-497-1726
>>>
>>> <http://www.cgd.ucar.edu/staff/asphilli>
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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
>>
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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

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