[gradsusr] question about meridional gradient computation in GRADS

[Jeff Duda]

1) You're plotting meridional temperature advection rather than just the
meridional gradient
2) units, units, units
3) The grid spacing of your data could impact the magnitudes of the final
product. Models run on finer grids can resolve higher winds and temperature
gradients. Taking the average might not fully cancel that out.

Jeff Duda

On Thu, May 11, 2017 at 1:19 AM, Lyndon Mark Olaguera <
olagueralyndonmark429 at gmail.com> wrote:

>
> Dear All,
>
> I am trying to compute the meridional gradient of of potential temperature
> (925hPa).
> Then create a latitude-time plot.
> I am getting very small magnitudes of the gradient which is not consistent
> with the literature that I am following (http://wwwoa.ees.hokudai.ac.
> jp/people/yamazaki/D/Dthesis_yOkada.pdf).
>
> Here's the script that I am using:
> 'sdfopen /mnt/dat/wind/vwind/10m/pentad_ensmean_vwnd_surf_1981-2010.nc'
>
> 'set display color white'
> 'c'
> 'set gxout shaded'
> 'set mpdset hires'
> 'set grid off'
> 'set grads off'
> 'set parea 0.5 8 2 10.5'
> 'set font 1'
> 'set lat -90 90'
> 'set lon 0 360'
> 'set dfile 1'
> 'set t 1 73'
> 'define t=pottmp'
> 'set dfile 2'
> 'set t 1 73'
> 'define u=uwnd'
> 'set dfile 3'
> 'set t 1 73'
> 'define v=vwnd'
>
> *'define dty = cdiff(t,y)'*
> *'define Re = 6.37e6'*
> *'define dy = Re*cdiff(lat,y)*(3.1416/180)'*
> *'define mergrad = -1*v*dty/dy'*
>
> 'set t 1 73'
> 'set lat 15 45'
> 'set x 1'
> 'set xyrev on'
> 'set xaxis 1 73'
> 'define a = ave(mergrad,lon=110,lon=120)'
> 'd a'
> 'cbarn'
> 'printim test.png'
> 'quit'
>
> Attached is the output image. In the literature,the unit is between -3 and
> 3, while in my case its x10-5.
>
>
> Any suggestions on how I can do this correctly?
>
>
> Lyndz
>
>
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>


-- 
Jeff Duda
Post-doctoral research fellow
University of Oklahoma School of Meteorology
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