[ncl-talk] Vorticity Advection with NCL

[Dennis Shea]

ESMF 37 was
(a)  interpolating u and v onto a rectilinear grid;
(b)  calculating divergence using uv2dv_cfd which requires u and v to be on
a rectilinear grid;
(c)  interpolating the derived divergence on a rectilinear grid back onto
the original WRF grid

---
In your case:

[1] Interpolate the WRF u, v and relative vorticity to a rectilinear grid
with as fine [or finer] resoultion as the WRF grid
[2] Use 'advect_variable' on the rectilinear grid
[3] interpolate the advected quantity on the rectilinear grid back onto the
original WRF grid

---
Caveat: Technically, on a sphere,  u and v must be interpolated together
using the 'rotation' angle.
Why? because the new location has a 'slightly' different orientation
relative to the pole(s)

  unew        = u*cos(rot) - v*sin(rot)
  vnew        = u*sin(rot) + v*cos(rot)

The above approach, independently interpolating u and v ignores the
rotation. It is assumed to be very small.




On Mon, May 21, 2018 at 3:45 AM, Lara Quitián Hernández <
laraquitianhernandez at gmail.com> wrote:

> Good morning,
>
> Thank you so much. Unfortunately, I have some doubts.
>
> 1.- I have read the information for Example 37 but I do not understand the
> need of computing the divergence ("uv2dv_cfd"). I just need my variables on
> a Gaussian, regular o fixed grid in order to apply the *advect_variable*
> function
> 2.- I need to convert my curvilinear WRF grid to a Gaussian, regular o
> fixed grid. However, in both Examples (29a and 37) a regrid from a WRF grid
> to a rectilinear grid is carried out. Are those grids (Gaussian, regular o
> fixed grid) also rectilinear grids?
> 3.-Do I need to regrid back to the WRF curvilinear grid as it is done in
> both examples?
>
> Thanks in advance.
>
> Regards,
> Lara
>
>
>
> 2018-05-20 1:10 GMT+02:00 Dennis Shea <shea at ucar.edu>:
>
>> NCL has no builtin function to advect a field (eg: vorticity) on a
>> curvilinear grid (eg: your WRF Grid)..
>> Maybe ask wrfhelp?
>>
>> ===
>> That said
>>
>> https://www.ncl.ucar.edu/Applications/ESMF.shtml
>> Example 29a
>> or, maybe better,
>> Example 37
>>
>> outlines a method that might be used for your needs.
>>
>> ===
>> Good luck
>>
>>
>> On Wed, May 16, 2018 at 7:40 AM, Lara Quitián Hernández <
>> laraquitianhernandez at gmail.com> wrote:
>>
>>> Hello,
>>>
>>> Thank you. In the case of calculating the horizontal advection for
>>> *vorticity*, it would be better to use the direct WRF variable ( vo =
>>> wrf_user_getvar(a,"*avo*",-1)) or define it via different functions:
>>> https://www.ncl.ucar.edu/Applications/vort.shtml
>>>
>>> The only example in the link defines the Vorticity like this:
>>>
>>> ;************************************************
>>> ; calculate vorticity on a Gaussian Grid
>>> ; scale for visual convenience
>>> ;************************************************
>>>   scale = 1.e05
>>>   vrt   = u                                      ; retain coordinates
>>>   vrt   = uv2vrG_Wrap(u,v) * scale
>>>   vrt at long_name = "vorticity"
>>>   vrt at units     = "scaled"
>>>
>>>
>>> However, my simulations are generated on a Lambert Conformal grid
>>> projection, not Gaussian one. Does this change the procedure to calculate
>>> it?
>>>
>>> Regards,
>>> Lara
>>>
>>> 2018-05-16 14:28 GMT+02:00 Dennis Shea <shea at ucar.edu>:
>>>
>>>> Maybe:
>>>>
>>>> https://www.ncl.ucar.edu/Document/Functions/Contributed/adve
>>>> ct_variable.shtml
>>>>
>>>> 'x' would be vorticity
>>>>
>>>> Good Luck
>>>>
>>>> On Wed, May 16, 2018 at 4:01 AM, Lara Quitián Hernández <
>>>> laraquitianhernandez at gmail.com> wrote:
>>>>
>>>>> Good morning,
>>>>>
>>>>> I would like to know if there is a possibility of calculating the
>>>>> Vorticity Advection with NCL.
>>>>>
>>>>> Thanks in advance.
>>>>>
>>>>> Regards,
>>>>> Lara
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>>
>>>>> *Lara Quitián Hernández, PhD Student*
>>>>> Departamento de Física de la Tierra, Astronomía y Astrofísica
>>>>> Facultad de Ciencias Físicas
>>>>> Ciudad Universitaria, Plaza Ciencias, 1
>>>>> <https://maps.google.com/?q=Ciudad+Universitaria,+Plaza+Ciencias,+1+28040+Madrid.+Spain&entry=gmail&source=g>
>>>>> 28040 Madrid. Spain
>>>>> <https://maps.google.com/?q=Ciudad+Universitaria,+Plaza+Ciencias,+1+28040+Madrid.+Spain&entry=gmail&source=g>
>>>>> Email: lquitian at ucm.es <mlunar at aemet.es>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> ncl-talk mailing list
>>>>> ncl-talk at ucar.edu
>>>>> List instructions, subscriber options, unsubscribe:
>>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>>
>>>>>
>>>>
>>>
>>>
>>> --
>>>
>>>
>>> *Lara Quitián Hernández, PhD Student*
>>> Departamento de Física de la Tierra, Astronomía y Astrofísica
>>> Facultad de Ciencias Físicas
>>> Ciudad Universitaria, Plaza Ciencias, 1
>>> <https://maps.google.com/?q=Ciudad+Universitaria,+Plaza+Ciencias,+1+28040+Madrid.+Spain&entry=gmail&source=g>
>>> 28040 Madrid. Spain
>>> <https://maps.google.com/?q=Ciudad+Universitaria,+Plaza+Ciencias,+1+28040+Madrid.+Spain&entry=gmail&source=g>
>>> Email: lquitian at ucm.es <mlunar at aemet.es>
>>>
>>>
>>
>
>
> --
>
>
> *Lara Quitián Hernández, PhD Student*
> Departamento de Física de la Tierra, Astronomía y Astrofísica
> Facultad de Ciencias Físicas
> Ciudad Universitaria, Plaza Ciencias, 1
> <https://maps.google.com/?q=Plaza+Ciencias,+1+28040+Madrid.+Spain&entry=gmail&source=g>
> 28040 Madrid. Spain
> <https://maps.google.com/?q=Plaza+Ciencias,+1+28040+Madrid.+Spain&entry=gmail&source=g>
> Email: lquitian at ucm.es <mlunar at aemet.es>
>
>
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