[ncl-talk] plotting geopotential height

[Guido Cioni]

Hey,

[1] it’s always preferable to use  wrfhelp at ucar.edu <mailto:wrfhelp at ucar.edu> for WRF-related issues with NCL. We generally don’t know so well the WRF functions so that we can not help if something it’s going wrong when interpolating/reading from WRF output files. However it seems that your problem it’s not strictly WRF related so I’ll give you my 2 cents on what is going wrong.

[2] when plotting any model variable @500 hPa you are getting the effect of the orography, especially with high mountains
 peaks like the ones found in the Rockies. In that area you are exactly getting the orography since isobaric levels intersect the mountains so that geopotential height corresponds with geometric height. So, from that point of view, you are getting exactly what you should from a model.

[3] you can mask the data over mountains with missing value so that NCL will automatically try to interpolate with values at lower altitudes. This can be easily achieved with the mask function and using the orography from the model output.

[4] you can smooth the geopotential height field but I doubt that will give you the correct results, since you’ll need to use a really strong filter to mask the effect of the mountains. I personally tried multiple times to use the smoothing functions of NCL and never worked out, so that I cannot give you a lot of advices regarding this option…but you can start from here http://www.ncl.ucar.edu/Document/Functions/Built-in/wrf_smooth_2d.shtml <http://www.ncl.ucar.edu/Document/Functions/Built-in/wrf_smooth_2d.shtml>

Regards,

Guido Cioni
http://guidocioni.altervista.org <http://guidocioni.altervista.org/> 

> On 07 Sep 2016, at 05:57, Lijun Diao <ljdiao at gmail.com> wrote:
> 
> Hi, everyone:
>  
> I am trying to plot 500 hpa geopotential height. I used wrf_user_getvar to get gh and wrf_user_intrp3d to interpolate to 500 hpa. Please verify I am doing right. 
>  
> gh             = wrf_user_getvar(b,"geopotential",-1)
> gh             = gh / 9.8 / 10.
> ; interpolation
> gh_plane       = wrf_user_intrp3d(gh, p, "h", 500, 0., False)
>  
> For the contour lines, I noticed there are a bunch of small circles over the Rocky Mountain as shown in the attached f1.png. What I want is a smoother plot as in the black lines in f2.png. Those small gh line circles actually coincide with the topograph as shown in f3.png. Please let me how I can plot a smooth gh as in f2.
>  
> thanks,
> -----------------------------------------------------------------------------
> Lijun Diao
> ldiao at uh.edu
> Research Assistant
> Department of Earth & Atmospheric Sciences
> University of Houston
> 4800 Calhoun RD., Bldg. S&R1-312
> Houston, TX 77204-5007
> <f1.png><f2.png><f3.png>_______________________________________________
> ncl-talk mailing list
> ncl-talk at ucar.edu
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ucar.edu/pipermail/ncl-talk/attachments/20160907/a9a9854e/attachment.html