On 2/21/2012 7:48 AM, Jim Biard wrote:
> John,
>
> Is this actually climatology data? If it were climatology data, it
> would usually be the average for a given hour, day, or whatever, where
> the average is taken over a decade or so. I think you may just need
> to apply regular bounds.
You might be right, Im trying to get clarification on this. Thanks for
your comments.
John
>
> Grace and peace,
>
> Jim
>
>
> On 2/20/2012 12:27 PM, John Caron wrote:
>> Im working with NOAA's CFSR dataset, reading it into the CDM, which
>> essentially means converting GRIB into CF/netCDF.
>>
>> ref:
>> http://nomads.ncdc.noaa.gov/data.php#cfs-reanal-data
>> http://dss.ucar.edu/datasets/ds093.2/
>>
>> from NCAR's DSS page:
>>
>> "CFSR monthly atmospheric, oceanic and land surface output products
>> are available as 6-hourly diurnal monthly means (00Z, 06Z, 12Z, and 18Z)"
>>
>> If I understand this correctly, the monthly mean data is as follows:
>>
>> for each month:
>> for each day of the month:
>> compute separate averages of the data at the 0,6,12, and 18Z
>> time coordinate.
>>
>> So one ends up with 4 time coordinates per month, and the data
>> represents the average for that month at that time. The time
>> coordinate is not a real calendar date, for example for the month
>> 2008-08, the time coordinate is not really
>>
>> 2008-08-01T00:00:00.000Z
>> 2008-08-01T06:00:00.000Z
>> 2008-08-01T12:00:00.000Z
>> 2008-08-01T18:00:00.000Z
>>
>> but more like:
>>
>> 2008-08-*T00:00:00.000Z
>> 2008-08-*T06:00:00.000Z
>> 2008-08-*T12:00:00.000Z
>> 2008-08-*T18:00:00.000Z
>>
>> where the * indicates an average over the days in that month.
>>
>> From
>>
>> http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/cf-conventions.html#climatological-statistics
>>
>> It appears that CF would represent this as:
>> dimensions:
>> time=4;
>> nv=2;
>>
>> variables:
>> float temperature(time,lat,lon);
>> temperature:long_name="surface air temperature";
>> temperature:cell_methods="time: point within days time: mean over days";
>> temperature:units="K";
>>
>> double time(time);
>> time:climatology="climatology_bounds";
>> time:units="days since 2008-01-01";
>>
>> double climatology_bounds(time,nv);
>>
>> data:
>> time="2008-08-01T00:00Z","2008-08-01T06:00Z","2008-08-01T12:00Z","2008-08-01T18:00Z" ;
>>
>> climatology_bounds="2008-08-01T00:00Z", "2008-08-31T00:00Z",
>> "2008-08-01T06:00Z", "2008-08-31T06:00Z",
>> "2008-08-01T12:00Z", "2008-08-31T12:00Z",
>> "2008-08-01T18:00Z", "2008-08-31T18:00Z" ;
>> Using "point within days" because we have an instantaneous quantity.
>>
>> However, im not sure what this sentence in 7.4 means: "When
>> considering intervals within days, if the earlier time of day is
>> equal to the later time of day, then the method is applied to a full
>> 24 hour day."
>>
>>
>> Another case is when the data are on time intervals, for example
>> "Total Precipitation Accumulation". In this case, the original data
>> are on time intervals which i represent as (start,end) dates:
>>
>> 2008-08-01T00:00:00.000Z, 2008-08-01T00:00:06.000Z
>> 2008-08-01T06:00:00.000Z, 2008-08-01T00:00:12.000Z
>> 2008-08-01T12:00:00.000Z, 2008-08-01T00:00:18.000Z
>> 2008-08-01T18:00:00.000Z, 2008-08-01T00:00:24.000Z
>> 2008-08-02T00:00:00.000Z, 2008-08-02T00:00:06.000Z
>> 2008-08-02T06:00:00.000Z, 2008-08-02T00:00:12.000Z
>> 2008-08-02T12:00:00.000Z, 2008-08-02T00:00:18.000Z
>> 2008-08-02T18:00:00.000Z, 2008-08-02T00:00:24.000Z
>> 2008-08-03T00:00:00.000Z, 2008-08-03T00:00:06.000Z
>> ...
>>
>> which are are averaged over days, giving 4 averages for each month,
>> which i denote as:
>>
>> 2008-08-*T00:00:00.000Z, 2008-08-*T00:00:06.000Z
>> 2008-08-*T06:00:00.000Z, 2008-08-*T00:00:12.000Z
>> 2008-08-*T12:00:00.000Z, 2008-08-*T00:00:18.000Z
>> 2008-08-*T18:00:00.000Z, 2008-08-*T00:00:24.000Z
>>
>> So perhaps this is:
>> dimensions:
>> time=4;
>> nv=2;
>>
>> variables:
>> float precipitation(time,lat,lon);
>> precipitation:long_name="surface air temperature";
>> precipitation:cell_methods="time: sum within days time: mean over days";
>> precipitation:units="K";
>>
>> double time(time);
>> time:climatology="climatology_bounds";
>> time:units="days since 2008-01-01";
>>
>> double climatology_bounds(time,nv);
>>
>> data:
>> time="2008-08-01T03:00Z","2008-08-01T09:00Z","2008-08-01T15:00Z","2008-08-01T21:00Z" ;
>>
>> climatology_bounds="2008-08-01T00:00Z", "2008-08-31T06:00Z",
>> "2008-08-01T06:00Z", "2008-08-31T12:00Z",
>> "2008-08-01T12:00Z", "2008-08-31T18:00Z",
>> "2008-08-01T18:00Z", "2008-08-31T24:00Z" ;
>> ??
>>
>>
>>
>>
>> thanks for any insights,
>> John
>>
>>
>>
>>
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>> CF-metadata at cgd.ucar.edu
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>
> --
> Jim Biard
>
> Government Contractor, STG Inc.
> Remote Sensing and Applications Division (RSAD)
> National Climatic Data Center
> 151 Patton Ave.
> Asheville, NC 28801-5001
>
> jim.biard at noaa.gov
> 828-271-4900
>
>
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Received on Fri Feb 24 2012 - 13:37:44 GMT
