From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>

Date: Thu Dec 01 2011 - 16:39:24 MST

Date: Thu Dec 01 2011 - 16:39:24 MST

I think Example 6 may have a documentation error.

The following

dTdX(:,:,nl,:) = center_finite_diff_n (T(:,:,nl,:), dX , True,0,0)

should be

dTdX(:,:,nl:nl,:) = center_finite_diff_n (T(:,:,nl:nl,:), dX , True,0,3)

---- dTdX(:,:,nl:nl,:) 0 1 2 3 <== dimension number the nl:nl forces the array to remain 4D so the dimension numbering stays the same. --- Let us know if this is the issue. +++++ Below ... if hus is already (time,lev,lat,lon) there would be no need to do this: hus(time|:,plev|:,lat|:,lon|:) On 12/1/11 4:17 PM, Nicole Schiffer wrote: > My goal is to calculate the 1-D moisture flux (mfu, mfv)and then use > that to figure moisture convergence. > > I was trying to follow Example 6 from the documentation > (http://www.ncl.ucar.edu/Document/Functions/Built-in/center_finite_diff_n.shtml). > I switched the dimension of n1,n2 because I want to look at divergence > rather than vorticity, as in an earlier post > (http://www.ncl.ucar.edu/Support/talk_archives/2010/2835.html). > > I also tried it using lat and lon without the looping or conversion from > degrees to distance just to get the function to work (see code below). > NCL still sees missing values in the u data and not in the v data (and > hence tries to calculate the gradient between real values and 1e+20). > > mfu(:,:,:,n2) = > center_finite_diff_n((hus(time|:,plev|:,lat|:,lon|:)/g)*ua(:,:,:,:),lon,False,0,2) > mfv(:,:,:,:) = > center_finite_diff_n((hus(time|:,plev|:,lat|:,lon|:)/g)*va(:,:,:,:),lat,False,0,2) > > -Nicole > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > * Nicole Schiffer > * Graduate Research Fellow (Dept. of Energy) > * Department of Atmospheric Sciences > * University of Illinois, Urbana-Champaign > * Email: nschiff2 [at] illinois [dot] edu > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > On 12/1/11 4:56 PM, Mary Haley wrote: >> Hi Nicole, >> >> Why are dx and dy calculated the way they are? >> >>> dx = 6378388*cos(0.0174533*lat(n2))*dlon >>> dy = 6378388.*0.0174533*dlon >> >> >> >> Did you mean to subscript "lat" with n2? You use "n2" as a longitude >> subscript >> in the center_finite_diff_n call, so I'm wondering if there's an error >> there... >> >> Something doesn't look quite right with the above code. I'm guessing >> one or >> both of dx or dy are incorrect. >> >> --Mary >> >> On Dec 1, 2011, at 10:31 AM, Nicole Schiffer wrote: >> >>> I'm using center_finite_diff_n on two 4D array (time, pressure, lat, >>> lon) with missing values. With one array, the u-wind, it handles missing >>> values fine. With the v-wind array, it doesn't. Both arrays have the >>> same metadata (missing and fill values). Any ideas why v-wind is a >>> problem? >>> >>> Code snippet: >>> dlat = 2.5*0.0174533 >>> dlon = dlat >>> do n2=0,nlon-1 >>> dx = 6378388*cos(0.0174533*lat(n2))*dlon >>> mfu(:,:,:,n2) = >>> center_finite_diff_n((hus(time|:,plev|:,lat|:,lon|n2)/g)*ua(:,:,:,n2),dx,False,0,2) >>> >>> end do >>> dlon = 2.5*0.0174533 >>> do n1=0,nlat-1 >>> dy = 6378388.*0.0174533*dlon >>> mfv(:,:,n1,:) = >>> center_finite_diff_n((hus(time|:,plev|:,lat|n1,lon|:)/g)*va(:,:,n1,:),dy,False,0,2) >>> >>> end do >>> >>> Thanks, >>> Nicole >>> >>> -- >>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>> * Nicole Schiffer >>> * Graduate Research Fellow (Dept. of Energy) >>> * Department of Atmospheric Sciences >>> * University of Illinois, Urbana-Champaign >>> * Email: nschiff2 [at] illinois [dot] edu >>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>> >>> _______________________________________________ >>> ncl-talk mailing list >>> List instructions, subscriber options, unsubscribe: >>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk >> > _______________________________________________ > ncl-talk mailing list > List instructions, subscriber options, unsubscribe: > http://mailman.ucar.edu/mailman/listinfo/ncl-talkReceived on Thu Dec 1 16:39:28 2011

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