Re: [ferret_users] Edges and @AVG

[Alexander Audet <alexander.c.audet@xxxxxxxxx>]

Afternoon Billy,

As far as I can tell (link) although the monthly means are timestamped at the first of the month and seem to be centered there, they actually represent the average value of the month instead 1/2 the last and 1/2 the named month. I am still confused about this, so I could be wrong. 

If so, by my understanding, it wouldn't be smoothing to recenter the data into the middle of the month?

Thank you for your comments! These are definitely details I need to think about!

Alexander Audet

On Tue, Feb 25, 2020 at 4:28 PM William S. Kessler <william.s.kessler@xxxxxxxx> wrote:

> On Feb 25, 2020, at 12:26 PM, Alexander Audet <alexander.c.audet@xxxxxxxxx> wrote:
>
> The full fix would probably be to first regrid it into proper 1-month time slots using the @ASN transformation as described in the above link, then regrid it a second time into the seasonal 3 months using the @AVG.

There's a danger here: The first step of averaging to put the data onto explicit months when the time points are centered on the first of the month is a smoothing operation before you start to do anything else. Won't that have a larger effect than the length-of-month problem?

It seems to me that "1/2 December, January, February, and 1/2 of March" is the right way (least smoothing) to define DJF. You could do this manually, or use @ave specifying dates; in that case if Ferret understands the calendar it will do this correctly.

Billy K