Dan,
How about that? I'm working on similar products. We haven't even
considered standard names for them.
I went ahead and used 'days since YYYY-MM-DD 00:00:00' for my first and
last frost dates, since they are valid dates. My files are structured as
(example for first frost date):
dimensions:
time = UNLIMITED ; // (56 currently)
lon = 960 ;
lat = 490 ;
bnds = 2 ;
variables:
double time(time) ;
time:standard_name = "time" ;
time:long_name = "time" ;
time:axis = "T" ;
time:units = "days since 1900-01-01 00:00:00" ;
time:calendar = "gregorian" ;
time:bounds = "time_bounds" ;
double time_bounds(time, bnds) ;
double lon(lon) ;
lon:standard_name = "longitude" ;
lon:long_name = "longitude" ;
lon:units = "degrees_east" ;
lon:modulo = 360. ;
lon:axis = "X" ;
lon:bounds = "lon_bounds" ;
double lon_bounds(lon, bnds) ;
double lat(lat) ;
lat:standard_name = "latitude" ;
lat:long_name = "latitude" ;
lat:units = "degrees_north" ;
lat:axis = "Y" ;
lat:bounds = "lat_bounds" ;
double lat_bounds(lat, bnds) ;
float first_freeze_date(time, lat, lon) ;
first_freeze_date:_FillValue = 1.e+20f ;
first_freeze_date:missing_value = 1.e+20f ;
first_freeze_date:comment = "Date of the first day
with a minimum temperature at or below 0 degrees C over the 9 month
period starting Aug 1 of each year." ;
first_freeze_date:flag_meanings =
"No_Freeze_Following" ;
first_freeze_date:long_name = "First freeze date" ;
first_freeze_date:valid_min = 0. ;
first_freeze_date:flag_values = -2. ;
first_freeze_date:units = "days since 1900-01-01
00:00:00" ;
first_freeze_date:calendar = "standard" ;
with the time bounds reflecting 1 Aug to 1 May for each year.
On 3/15/17 1:50 PM, Hollis, Dan wrote:
>
> Hi Jon,
>
> I?d be interested to know how to tackle this problem too. I?ve
> recently been generating some datasets of ?date of first frost? and
> ?date of last frost? and have no idea how to describe them in a
> CF-compliant way.
>
> Jim?s suggestion of ?day_of_year? is better than just ?days?, however
> this doesn?t capture what the ?something? is that has happened, nor
> that is the first/last/Nth occurrence of that event. What sort of
> events are you looking at?
>
> In my application I?m just looking at UK data, hence my ?year? runs
> from 1^st July to 30^th June (to span the N Hemisphere winter). It?s
> easy enough to use the bounds to indicate this, but I?m then not sure
> what values to store in the data array. Number of days since 1^st July
> maybe? Or ordinal date (1^st Jan = 1, 31^st Dec = 365)?
>
> Dan
>
> PS I have a whole bunch of other metrics that I?m looking at e.g.
> length of the longest spell, number of spells greater then N days etc.
> These seem even more complicated to describe using CF. Something for
> another post I think...
>
> *From:*CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] *On
> Behalf Of *Jim Biard
> *Sent:* 15 March 2017 16:28
> *To:* cf-metadata at cgd.ucar.edu
> *Subject:* Re: [CF-metadata] Recording "day of year on which something
> happens"
>
> Jon,
>
> I agree that a cell_methods attribute doesn't seem to be necessary. A
> new standard_name like 'day_in_year' or 'day_of_year' would likely
> make things clearer.
>
> Jim
>
> On 3/15/17 11:22 AM, Jon Blower wrote:
>
> Thanks Jim, that?s very helpful. Is cell_methods necessary in this
> case (for the time axis bounds) ? probably not since this isn?t a
> statistical quantity like an average, but a value that?s
> ?representative? of the year.
>
> I seem to remember from a while back that there was a proposal to
> allow time axes to use ?calendar years since X? (as opposed to
> ?years since X?, which uses a fixed-length UDUNITS year), which
> might handle this use case. I have been out of the loop for a
> while, but I can?t find mention of that in the CF spec, so maybe
> that didn?t go through.
>
> I might consider requesting a new standard name ? ?days? is good,
> but I wonder if a more specific one would be helpful.
>
> Best wishes,
> Jon
>
> *From: *CF-metadata <cf-metadata-bounces at cgd.ucar.edu>
> <mailto:cf-metadata-bounces at cgd.ucar.edu> on behalf of Jim Biard
> <jbiard at cicsnc.org> <mailto:jbiard at cicsnc.org>
> *Date: *Tuesday, 14 March 2017 15:12
> *To: *"cf-metadata at cgd.ucar.edu" <mailto:cf-metadata at cgd.ucar.edu>
> <cf-metadata at cgd.ucar.edu> <mailto:cf-metadata at cgd.ucar.edu>
> *Subject: *Re: [CF-metadata] Recording "day of year on which
> something happens"
>
> Jon,
>
> 1) I'd use 'days'. It is a valid standard name apart from the
> 'days since date' formalism. It's not perfect, but it's legal. You
> could, alternatively, request a new standard name.
>
> 2) Use a time_bounds variable. I would tend to set the time to be
> July 1 at midnight for each year, and set the bounds for each year
> to Jan 1 of that year and Jan 1 of the next year.
>
> Grace and peace,
>
> Jim
>
> On 3/14/17 10:43 AM, Jon Blower wrote:
>
> Hi all,
>
>
>
> We need to structure a NetCDF file that will hold a variable that represents the day of the year on which an event happened (integers from 0 to 366). This value is recorded every year for a number of years. I have a couple of questions about how best to do this:
>
>
>
> 1. What is the best standard name to use for the day of the year? I didn?t find anything in the standard name table, although I might have missed it.
>
>
>
> 2. What would be the best way to define the time axis? Each point along the axis would represent a whole year, rather than an instant in time. I could simply pick an arbitrary instant (e.g. midnight on 1st Jan) to represent the year, but is there a better way?
>
>
>
> Thanks in advance for any help!
>
>
>
> Jon
>
>
>
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Received on Wed Mar 15 2017 - 12:16:19 GMT
