# regridding/transforming from monthly to annual

```
I am fairly new to ferret and don't have all the concepts straight yet.
This question may be very elementary, but I can't solve it:

I have a monthly time series of 2-D data (lat x lon) in a netCDF file. I
want to aggregate (sum) the monthly data to annual values. A dynamic
regridding like:

LET eetan = eet[GL=1:84:12@SUM]

works just fine; I'm then able to plot it as, for example:

plot eetan[x=-70,y=-5]

However, it seems that I have to DEFINE a new axis/grid in order to plot,
say the x-y data for one particular year using SHADE. I tried (borrowing
from the Ferret FAQ pages and the release 4.20 notes):

DEFINE AXIS/T="1-JUL-1983":"1-JUL-1989"/UNIT=year tannual
DEFINE GRID/LIKE=eet/T=tannual gannual

LET eetan = eet[GT=tannual@SUM]

But it didn't work -- the define axis statement gave me an error message
saying that the lo:high:delta notation is wrong. There is no delta in this
statement, but this is exactly what was in one of those documents. Adding
some sort of delta value didn't help either. And using something like:

DEFINE AXIS/T=0:83:12/UNITS=years tannual

also didn't work.

What am I doing wrong?

Also, when the @SUM transform is applied, how do I make sure that it is
applied over the desired months (ie, jan-dec, instead of jul-june)? In the
statement above, does the 12-unit box start at the first value (T=0, so
that the result is 0->11, 12->23, etc), or is it *centered* around the
first value (-6->5, 6->17, etc)?

Thanks!

Emilio Mayorga
_________________________________________________________________
University of Washington
School of Oceanography			emiliom@u.washington.edu
Box 357940				ph. (206) 543-5334
Seattle, WA  98195-7940	  USA		FAX (206) 685-3351
http://boto.ocean.washington.edu/staff_pages/emilio/

```