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<body class='hmmessage'><div dir='ltr'><span style="color: rgb(68, 68, 68); font-size: 15px; line-height: 21.299999237060547px; background-color: rgb(255, 255, 255);">Hi,</span><div style="line-height: 21.299999237060547px; color: rgb(68, 68, 68); font-size: 15px; background-color: rgb(255, 255, 255);"><br></div><div style="line-height: 21.299999237060547px; color: rgb(68, 68, 68); font-size: 15px; background-color: rgb(255, 255, 255);">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 style="line-height: 21.299999237060547px; color: rgb(68, 68, 68); font-size: 15px; background-color: rgb(255, 255, 255);"><br></div><div style="line-height: 21.299999237060547px; color: rgb(68, 68, 68); font-size: 15px; background-color: rgb(255, 255, 255);">Thanks,</div><div style="line-height: 21.299999237060547px; color: rgb(68, 68, 68); font-size: 15px; background-color: rgb(255, 255, 255);">David </div><div style="line-height: 21.299999237060547px; color: rgb(68, 68, 68); font-size: 15px; background-color: rgb(255, 255, 255);"><br></div><div style="line-height: 21.299999237060547px; color: rgb(68, 68, 68); font-size: 15px; background-color: rgb(255, 255, 255);"><div>fobj = addfile("~/data/CFSR/cmd_grblow/1979/pgblnl.gdas.1979123118.grb2","r")</div><div><span style="line-height: 22.719999313354492px; 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="line-height: 22.719999313354492px; 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="line-height: 22.719999313354492px; font-size: 12pt;">gsn_panel(wks,plot,(/2,1/),False)</span></div><div><span style="line-height: 22.719999313354492px; font-size: 12pt;"><br></span></div></div> </div></body>
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