[Thread Prev][Thread Next][Index]
weird regridding behavior
I'm using Ferret 4.91 on an SGI irix64 6.2 (had no luck installing v5.0).
I have a series of NCEP/NCAR daily reanalysis netCDF files. I want to
regrid them to a 2x2 degree grid, from a 2.5x2.5 degree grid. The
original grid is:
yes? show grid air
GRID GMH1
name axis # pts start end
LON LONGITUDE 144mr 0E 2.5W
LAT LATITUDE 73 r 90S 90N
normal Z
TIME TIME 365 r 03-JAN-1978 00:00 02-JAN-1979
00:00
(The days are off by 2 because of the udunits issue.)
The grid I defined is:
define axis/x=0:358:2/unit=degrees/modulo xax
define axis/y=90s:40s:2/unit=degrees yax
define grid/x=xax/y=yax gfine
I've tried two methods to get what I want using the new grid and neither
work.
The first thing I tried was to regrid directly onto grid gfine
"air[g=gfine]". But I get one less than the expected dimension in X (ie,
179 values, from 0e to 356 by 2.
Since both the orignal and new grid are defined modulo in X I don't
understand why the regridding won't act the way I expect, ie, to give 180
values in X, using the modulo function to interpolate between 357.5 and
0.0. On the other hand, at least there are no missing values in longitude
(not that I expect any, but see below):
yes? list/y=60s/l=1 air
mean Daily Air temperature at sigma leve (degK)
regrid: 2 deg on X, 2 deg on Y
TIME: 03-JAN-1978 00:00
DATA SET: ./regrid_1.cdf
60S
16
0E / 1: 272.5
2E / 2: 272.5
4E / 3: 272.4
6E / 4: 272.3
8E / 5: 272.3
10E / 6: 272.4
12E / 7: 272.5
14E / 8: 272.6
16E / 9: 272.6
18E / 10: 272.5
The second way I tried was to explicity tell ferret to regrid on the X
axis using modulo regridding "air[gx=xax@mod,gy=yax]". In this case I get
regridded values with the expected dimensions in X (ie, 180 values, from 0
to 358 by 2) but, every 5th value comes up missing:
yes? list/y=60s/l=1 air
mean Daily Air temperature at sigma leve (degK)
regrid: 2 deg on X@MOD, 2 deg on Y@LIN
TIME: 03-JAN-1978 00:00
DATA SET: ./regrid_2.cdf
60S
16
0E / 1: 272.5
2E / 2: 272.5
4E / 3: ....
6E / 4: 272.3
8E / 5: 272.3
10E / 6: 272.4
12E / 7: 272.6
14E / 8: ....
16E / 9: 272.7
18E / 10: 272.5
Does anyone have an explanation for what's going on here? And, more
importantly, how to get the regridding to do what I want?
Thanks,
Denise
=====================================================================
Denise L. Worthen, SSAI
Oceans and Ice Branch/Code 971
NASA Goddard Space Flight Center
Greenbelt MD 20771
dlw@weka.gsfc.nasa.gov
(301) 286-2339
[Thread Prev][Thread Next][Index]
Dept of Commerce /
NOAA /
OAR /
PMEL /
TMAP
Contact Us | Privacy Policy | Disclaimer | Accessibility Statement