<div dir="ltr"><div>As noted in the <em>documentation:<br><br><a href="https://www.ncl.ucar.edu/Document/Functions/Built-in/uv2vrF.shtml">https://www.ncl.ucar.edu/Document/Functions/Built-in/uv2vrF.shtml</a><br><br></em></div>
<em>[SNIP]</em><ul><li>input values must be in ascending latitude order <**********<br></li><li>input array must be on a global gri
</li></ul><p>========<br></p><p>Typically, NCEP, ECMWF, etc are ordered N=>S. You want S=>N</p><p> ugrd = ugrd(:,:,::-1,:) ; time,lev,lat,lon<br></p><p> vgrd = ugrd(:,:,::-1,:)</p><p><br></p><p>or , 3D<br></p><p>
ugrd = ugrd(:,::-1,:) ; time,lat,lon<br></p><p> vgrd = ugrd,:,::-1,:)</p><p><br></p></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Aug 15, 2014 at 2:15 PM, David Wang <span dir="ltr"><<a href="mailto:dw2116@outlook.com" target="_blank">dw2116@outlook.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div dir="ltr">Hi,<div><br></div><div>It is said in the documentation that uv2vrF is more accurate than uv2vr_cfd if the input velocity data are global and have no missing values. However, I found that using the 2.5x2.5-degree CFSR data, the relative vorticity field computed with uv2vr_cfd is almost identical to the CFSR output for absolute vorticity minus planetary vorticity (f); whereas the relative vorticity field computed with uv2vrF is quite different. I wonder if I missed anything obvious and didn't use uv2vrF correctly. Below is my NCL code.</div>
<div><br></div><div>Thanks,</div><div>David </div><div><br></div><div><div>fobj = addfile("~/data/CFSR/cmd_grblow/1979/pgblnl.gdas.1979123118.grb2","r")</div><div><span style="font-size:12pt">absv = fobj->ABSV_P0_L100_GLL0({50000},:,:) ;absolute vorticity</span></div>
<div>ugrd = fobj->UGRD_P0_L100_GLL0({50000},:,:) ; zonal velocity</div><div>vgrd = fobj->VGRD_P0_L100_GLL0({50000},:,:) ; meridional velocity</div><div><br></div><div>; Compute relative vorticity from zonal/meridional velocity</div>
<div>vort = ugrd</div><div>vort = uv2vrF(ugrd,vgrd)</div><div>;vort = uv2vr_cfd(ugrd,vgrd,ugrd&lat_0,ugrd&lon_0,1)</div><div><br></div><div>; Compute relative vorticity from absolute vorcitity</div><div>rad = 4.*atan(1.)/180.</div>
<div>clat = fobj->lat_0</div><div>f = 2*7.2921e-5*sin(rad*clat)</div><div><span style="font-size:12pt">relv = absv</span></div><div>relv = absv - conform(absv,f,0)</div><div>relv@long_name = "Relative vorticity"</div>
<div><br></div><div>wks = gsn_open_wks("x11","relative.vorticity")</div><div>res = True</div><div>res@gsnDraw = False</div><div>res@gsnFrame = False</div><div>res@cnFillOn = True</div><div>res@cnLinesOn = False</div>
<div>symMinMaxPlt(relv,20,False,res)</div><div>plot = new(2,graphic)</div><div>plot(0) = gsn_csm_contour_map(wks,relv,res)</div><div>plot(1) = gsn_csm_contour_map(wks,vort,res)</div><div><span style="font-size:12pt">gsn_panel(wks,plot,(/2,1/),False)</span></div>
</div><div><br></div> </div></div>
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<br></blockquote></div><br></div>