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strange thing about the grid
Hello, there: I have this weird thing with my underlying grid, and could not
figure out why. Here is what happened:
I have a 52 year monthly mean data from NCEP reanalysis. The underlying t axis
is irregular and centered on the 15/16th of each month. I was trying to extract
a particular month from that long time series by doing
let mar = temp[l=3:624:12]
let apr = temp[l=4:624:12]
....
But, the problem is that I can only do ONE MONTH per time. If I had more than
one definition, the ferret would give me the same value/grid of apr as mar. Here
is an example:
yes? show grid mar
GRID (G002)
name axis # pts start end
LON LONGITUDE 144mr 0E 2.5W
LAT37_73 LATITUDE 37 r 0 90N
LEVEL HEIGHT (millib 17 i- 10 1000
(AX006) TIME 52 i 16-MAR-1948 12:00 16-MAR-1999 12:00
yes? show grid apr
GRID (G002)
name axis # pts start end
LON LONGITUDE 144mr 0E 2.5W
LAT37_73 LATITUDE 37 r 0 90N
LEVEL HEIGHT (millib 17 i- 10 1000
(AX006) TIME 52 i 16-MAR-1948 12:00 16-MAR-1999 12:00
yes?
But if I do
yes? can var mar
yes? show grid apr
GRID (G002)
name axis # pts start end
LON LONGITUDE 144mr 0E 2.5W
LAT37_73 LATITUDE 37 r 0 90N
LEVEL HEIGHT (millib 17 i- 10 1000
(AX005) TIME 52 i 16-APR-1948 00:00 16-APR-1999 00:00
Now the definition for apr is correct, and values are fine, too. It seems that
ferret only can recognize one definition like that, the first one.
However, if I define a regular monthly grid like
yes? define axis/t=15-jan-1948:15-dec-1999:30.44/units=days treg
yes? define grid/t=treg grdnew
and then regrid the data to this new evenly spaced grid
yes? let tnew = temp[g=grdnew]
yes? let mar = tnew[l=3:624:12]
yes? let apr = tnew[l=4:624:12]
Now it works fine:
yes? show grid mar,apr
GRID (G002)
name axis # pts start end
LON LONGITUDE 144mr 0E 2.5W
LAT37_73 LATITUDE 37 r 0 90N
LEVEL HEIGHT (millib 17 i- 10 1000
(AX005) TIME 52 r 15-MAR-1948 21:07 18-MAR-1999 03:50
GRID (G004)
name axis # pts start end
LON LONGITUDE 144mr 0E 2.5W
LAT37_73 LATITUDE 37 r 0 90N
LEVEL HEIGHT (millib 17 i- 10 1000
(AX007) TIME 52 r 15-APR-1948 07:40 17-APR-1999 14:24
yes?
Any idea on what's going on?
Thanks for your thought.
Muyin
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