[ncl-talk] vfXArray and vfYArray

[Sheng-Hung Wang]

Thanks for response.

After all kind trials and errors. We kind of figure U10E and V10E with

resstream at vfXArray               = lon2d
resstream at vfYArray               = lat2d
resstream at tfDoNDCOverlay     = False
resstream at gsnAddCyclic           = False

Is the only way working.

So guess we need to calculate those earth-relative components 1st for 
the similar studies.


On 6/21/2017 4:08 PM, David Brown wrote:
> The problem is that you are using grid-relative vector components.
> These are only good when drawing in the native projection with no
> mapping of the coordinates. In NCL terms, it means only when you set
> tfDoNDCOverlay True.
>
> Fortunately your data file also contains the earth-relative components
> that work when the data is mapped into a projection (even if the
> projection produces the same map as the native grid).  You just need
> to substitute U10E and V10E for U10M and V10M. I have created a
> modified version of your script that draws the grid-relative and the
> earth-relative data so you can clearly see the difference.
>
> I should note that often WRF files do not contain the earth-relative
> components, but in many cases instead contain vector rotation
> variables that you can apply to transform from grid-relative to
> earth-relative components.
>
> The modified script produces three plots: first the native ("raw")
> plot, then a grid-relative plot wrongly mapped into the projection,
> and finally an earth-relative plot that should be correct (attached).
> I chose to use curly vectors instead of streamlines because the
> direction of flow is more obvious.
>
>
>
> On Fri, Jun 16, 2017 at 8:52 AM, Sheng-Hung Wang <wang.446 at osu.edu> wrote:
>> Hi there
>>
>> This is Sheng-Hung from BPCRC at the OSU. We are trying to plot wind
>> (U10M, V10M and SPD10M) from WRF model output.  The data files are
>> extracted from wrfout files.
>>
>> As you can see in native model grids (plot_raw.png or plot_raw.ncgm) plot,
>>
>> The winds rotate in clockwise direction at Atlantic Ocean (upperright
>> corner), and counter clockwise at east of Greenland (just above map
>> center).
>>
>> However, after using vfXArray and vfYArray and plot on map (plot.png or
>> plot.ncgm),
>>
>> The winds rotate in opposite directions.
>>
>> The winds over Pacific are still in an agreement (directions and
>> patterns) with model native grids.
>>
>> I tried  NCL 6.4 6.3.x, running on Fedora, all produced same results.
>>
>> Is there a problem with vfXArray/vfYArray functions or did I something
>> wrong in my script.
>>
>> You can find my script/data/plots in
>>
>> http://polarmet.osu.edu/datasets/proj_201706/
>>
>> Thanks
>>
>>
>> Sheng-Hung
>>
>> ps. I also tested sfXArray/sfYArray on each individual variables. The
>> plots are fine.
>>
>> --
>> ========================================
>>    Sheng-Hung Wang, PhD
>>    Polar Meteorology Group
>>    Byrd Polar and Climate Research Center
>>    The Ohio State University
>>    1090 Carmack Road, Columbus, Ohio 43210
>>    Phone: (614) 292-1060
>>    Fax:   (614) 292-4697
>>    email: wang.446 at osu.edu
>> ========================================
>>
>> _______________________________________________
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-- 
========================================
  Sheng-Hung Wang, PhD
  Polar Meteorology Group
  Byrd Polar and Climate Research Center
  The Ohio State University
  1090 Carmack Road, Columbus, Ohio 43210
  Phone: (614) 292-1060
  Fax:   (614) 292-4697
  email: wang.446 at osu.edu
========================================