Question of interpolation on missing values.

Hi all,
I use a cutoff freqency for 7 day to get low pass filter potential
vorticity. Then I calculate the gradient of this potential vorticity by
using the function "gradsg". When I run my script, it shows that "warning:
gradsg: 6 2-dimensional input array(s) contained missing values. No
interpolation performed on these arrays." My result looks reasonable even
though this warning exists. I try to use "linmsg" to interpolate missing
values before computing their gradient. But the warning still existed and
the pattern is wrong. My script is attached below.

I would be very appreciated if people can give me some suggestions. Thanks
a lot,

Yi-Hui

load "/usr/lib/ncarg/ncarg/nclscripts/csm/contributed.ncl"

begin

yr = new((/160/),float)
yr = 0
do n = 1,80
  yr(n-1) = n
  yr(79+n) = n + 100
end do
Q_sum = new((/152,64,128/),float)
Q_sum = 0

;open files of 160 ensemble members
do i=0,159
  if (yr(i) .lt. 10) then
    name="./ctl_PV_00" + yr(i) + ".nc"
  else
    if (yr(i) .lt. 100) then
      name="./ctl_PV_0" + yr(i) + ".nc"
    else
      name="./ctl_PV_" + yr(i) + ".nc"
    end if
  end if
  f = addfile(name,"r")
  lat = f->lat
  lon = f->lon
  PV = f->PV_total(:,:,:)

  ;low pass filter
  nwt = 7
  fca = 1.0/7.0
  ihp = 0
  nsigma = 1.
  wgt = filwgts_lancos(nwt,ihp,fca,-999.,nsigma)
  PVf = wgt_runave_Wrap(PV(lat|:,lon|:,time|:),wgt,0) ;64*128*152

  PVf!0="lat"
  PVf!1="lon"
  PVf!2="time"
  PVf_reorder = PVf(time|:,lat|:,lon|:)
  PVf_reorder!0="time"
  PVf_reorder!1="lat"
  PVf_reorder!2="lon"

  ;try linmsg, PVf_new replaces PVf_reorder in gradsg
  ;msg = 1e36
  ;PVf_reorder@_FillValue = msg
  ;PVf_new = linmsg(PVf_reorder,-1)
  ;PV_grad_lon = PVf_new
  ;PV_grad_lat = PVf_new

  ;calculate the gradient
  PV_grad_lon = PVf_reorder
  PV_grad_lat = PVf_reorder
  gradsg(PVf_reorder,PV_grad_lon,PV_grad_lat)
  PV_grad_lon_at_long_name = "PV longitudinal gradient (derivative)"
  PV_grad_lat_at_long_name = "PV latitudinal gradient (derivative)"
  Q = sqrt((PV_grad_lon(:,:,:))^2 + (PV_grad_lat(:,:,:))^2)
  Q_sum = Q_sum + Q(:,:,:)
  copy_VarCoords(Q,Q_sum)

  delete(PV)
  delete(PVf)
  delete(PVf_reorder)
  delete(PV_grad_lon)
  delete(PV_grad_lat)
  delete(Q)
end do
  ;average Q from all ensemble members
  Q_avg = Q_sum/160
  copy_VarCoords(Q_sum,Q_avg)
end

Yi-Hui Wang
Graduate Student
2101D Croul Hall, Dept of Earth System Science
University of California at Irvine
Irvine, CA 92697-3100
yihuiw_at_uci.edu
949-824-8448

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Received on Tue Nov 04 2008 - 12:18:38 MST