Hi Karl,
This is a real use case for us too. And not just for short climatologies. When we compute our 30-year normals we use only the data from those 30 calendar years e.g. for 1981-2010 normals we use data from Jan 1981 to Dec 2010. Like you we create monthly normals first and then combine these to create seasonal normals. I'd not come up with a way to describe the result in a CF-compliant way so I was interested to see your question.
Using daily maximum temperature as an example, I guess what we are doing is something like this:
time: maximum within days time: mean over days time: mean over years time: mean over months
where 'mean over days' means over the days within each calendar month
and 'mean over months' means over the months within a season
I cannot immediately see how to extend/adapt the convention to allow for this possibility.
Regards,
Dan
-----Original Message-----
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Karl Taylor
Sent: 11 February 2016 20:50
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] How to build CF-compliant seasonal climatology when data begins within a season
Hi Jonathan,
Our thinking is the same on this. Thanks.
By the way it is a real use case and I think it is scientifically
defensible: I have 11 full years of data and I first compute a climatological annual cycle, yielding 12 climatological months. Then I compute the climatology for each of the seasons from the monthly climatology. This allows me to use all the data in the 11 years. I especially would want to do it this way if I only had 2 or 3 years of data because I wouldn't want to omit any of it.
[Of course you wouldn't be able to do this if you were calculating say a trend of individual seasons; in that case you clearly wouldn't want to consider partial seasons.]
best wishes,
Karl
On 2/11/16 12:20 PM, Jonathan Gregory wrote:
> Dear Karl
>
> I agree with Seth that this isn't anticipated by the design of the
> convention, which assumes that the mean over seasons is composed of a
> number of complete seasons. Is this a real use-case, with a DJF mean
> made by including JF from one NH winter and D from another? It seems a
> bit odd to me. I wouldn't compute a monthly mean of anything if 2/3 of
> the days were missing in the month. But, following this logic, your
> original choice of "1999-12-1" to "2011-3-1" is OK, and it "just
> happens" that Dec 1999 and Jan-Feb 2011 are actually not included, as
> if they were missing data. Their omission is not recorded by the
> climatology bounds but, equally, if Dec 2005 or Jan-Feb 2008 (for
> example) were missing when computing the mean you would not know about it from the climatology bounds. So perhaps it doesn't matter.
>
> To spell out exactly which months were used, it would be necessary to
> record also the time coordinate and bounds before the collapse. In
> various tickets we have discussed but not agreed a convention for doing that, as extra info.
> Alternatively you could record it as unstandardised info as a comment
> in () in the cell_methods, as you note.
>
> Best wishes
>
> Jonathan
>
> ----- Forwarded message from Karl Taylor <taylor13 at llnl.gov> -----
>
>> Date: Wed, 10 Feb 2016 15:37:01 -0800
>> From: Karl Taylor <taylor13 at llnl.gov>
>> To: cf-metadata at cgd.ucar.edu
>> Subject: [CF-metadata] How to build CF-compliant seasonal climatology when
>> data begins within a season
>> User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:38.0)
>> Gecko/20100101 Thunderbird/38.5.1
>>
>> Dear CF community,
>>
>> In representing the seasonal climatology based on data available for
>> the period January 1, 2000 through December 31 2010, what would be
>> the correct climatology_bounds?
>>
>> climatology_bounds = "1999-12-1", "2011-3-1",
>> "2000-3-1", "2010-6-1",
>> "2000-6-1", "2010-9-1",
>> "2000-9-1", "2010-12-1" ????
>>
>> I would note that this seems to capture the idea that we are
>> reporting seasonal means, but it also seems to indicate that this is
>> based in part on data from Dec. 1999 and Jan.-Feb. 2011, when it
>> isn't. Is this the best I can do? [Of course the convention can
>> never tell us if data are complete in forming a climatology. If 1
>> year were missing, this would not affect the attributes.]
>>
>> I suppose the in the cell_methods attribute ("time: mean over days
>> time: mean over years" I could add non-standardized information (as
>> permitted by CF), for example: "time: mean over days time: mean
>> over years (with data from the period 2000-1-1 to 2011-1-1)"
>>
>> thanks for any suggestions,
>> Karl
>>
>>
>>
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> ----- End forwarded message -----
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Received on Mon Feb 15 2016 - 05:02:04 GMT
