[ferret_users] dealing with monty-mean time series

[Sang-ki Lee <Sang-ki.Lee@xxxxxxxx>]

Hi,

I have a general question about dealing with monthly-averaged
time series data from different sources.

NCEP1 reanalysis data is a good example. The original (grib format)
data from NCEP have the time index at the beginning of each month,
like 01/JAN/1949, 01/FEB/1949, and etc. One has to be very careful,
because this time index means "initial_time" of the monthly average.
For instance, t=01/JAN/1949 means time average from 01/JAN/1949 to
31/JAN/1949. If one download the CDC-derived NCEP1 reanalysis data
(netcdf format), sometimes the time index is relocated to the
middle of each month.

If I want to mix the original NCEP1 data with the cdc-derived
data, one thing that I should not do is to regrid the original
NCEP1 data to the time index of CDC-derived data in the following
way:

ex) err = sst_cdc - sst_org[gt=sst_cdc]

This is like mixing orange and apple. In my case, I do the
following:

let err = sst_cdc - sst_org[gt=month_reg@asn]
or
let err = sst_cdc[l=1:660] - sst_org[l=1:660]

However, I find such regriding processes time-consuming and
unnecessary. And, it is also very easy to make mistake. I always
get ambiguous time axis warning when I do this way, but I guess
that is ok.

It will be very convenient if there is a way to tell Ferret
to ignore the day, hour and second. So whenever Ferret see JAN/1949,
for instance, it automatically understand that the date is in the
middle of JAN/1949.

I would welcome any other tips for dealing with monthly-mean time
series data.

Sang-ki

--
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Dr. Sang-ki Lee
RSMAS/CIMAS
University of Miami
4600 Rickenbacker Causeway
Miami, FL 33149 USA
Tel) 305-361-4521
Fax) 305-361-4412
E-mail) sang-ki.lee@noaa.gov
Homepage) http://www.aoml.noaa.gov/phod/people/sklee.html
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Mailing-address:
Dr. Sang-ki Lee
AOML/PHOD
4301 Rickenbacker Causeway
Miami, FL, 33149 USA
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