we get the reference time from Identification section (GRIB2), or pds
section (octet 13-17) (GRIB1).
On Tue, Mar 3, 2015 at 8:23 AM, Don Murray (NOAA Affiliate) <
don.murray@xxxxxxxx> wrote:
> Hi John-
>
> Thanks for the updates. Are you looking at determining this for a dataset
> from the analysis/forecast hour 0 fields in a dataset, or from the
> reference time in each GRIB record?
>
> Don
>
> On 3/2/15 5:06 PM, John Caron wrote:
>
>> Hi Don:
>>
>> The CDM now has an "auxiliary coordinate" that gives the reference time
>> (aka run time) for each valid time in a Best dataset. We are working
>> with the IDV group to help them show that info to the user.
>>
>> Currently we are looking at the presence of analysis vs forecast GRIB
>> records in the NCEP datasets to see what makes sense there. As usual,
>> its not really clear what different groups do when they generate GRIB,
>> so we are trying to be careful not to assume too much.
>>
>> All this work is being done on the 4.6 development branch.
>>
>> Thanks for your comments.
>>
>> John
>>
>>
>>
>> On Wed, Feb 11, 2015 at 2:54 PM, Don Murray (NOAA Affiliate)
>> <don.murray@xxxxxxxx <mailto:don.murray@xxxxxxxx>> wrote:
>>
>> Hi Ryan-
>>
>> I think this sounds like a workable solution. I assume that the
>> Complete is essentially how the Best works now. Given the problems
>> it has, I'm not sure if it's needed. An Analysis dataset would be a
>> good addition.
>>
>> And of course, it would be good to be able to query any timestep for
>> the model run time so the forecast hour can be computed.
>>
>> Will this be an update to 4.5 or will we have to wait for 4.6?
>>
>> Thanks for attacking this problem.
>>
>> Don
>>
>>
>> On 2/11/15 11:24 AM, Ryan May wrote:
>>
>> Greetings!
>>
>> The recent upgrades by NCEP to the time range of the operational
>> GFS
>> half degree output has raised an issue with the Best timeseries
>> dataset
>> on Grib Collections in TDS. Best is designed to take all the
>> forecast
>> times available in the Grib Collection and, for each one, use
>> the GRIB
>> record that has the smallest forecast offset (i.e. the forecast
>> closest
>> to the start of its model run).
>>
>> The problem occurs where, for example, NCEP puts out GFS runs
>> every 6
>> hours, but at the later parts of the forecast, the time interval
>> within
>> a single run's output is 12 hours. The result is that even with no
>> missing data, eventually the Best time series has output every 6
>> hours
>> by interleaving two different forecasts. Given that forecasts
>> this far
>> into the future can vary widely from run to run, this can yield
>> very
>> surprising and confusing results. Note that this issue is not
>> limited to
>> the GFS, but for any model collection where time steps in the
>> output
>> become larger than the time between individual model runs.
>>
>> There is also a second issue regarding a model run having multiple
>> fields with a 0 hour forecast offset. It turns out that (at least
>> ideally) NCEP will put out one version of the 0 hour forecast
>> with the
>> analysis flag set, denoting the field as the one to use to
>> initialize
>> the model. Then a second field is put out as 0 hour forecast
>> (without
>> the analysis flag) that actually corresponds to a time after a
>> single
>> model integration step. This non-analysis 0 hour forecast
>> contains the
>> full collection of parameters that are available throughout the
>> forecast, whereas the analysis only contains the fields that
>> result from
>> data assimilation. Currently, the Best time series will contain
>> whichever version of the 0 hour forecast that comes first in the
>> file.
>>
>> To address the first issue and make the data easier to use, we
>> propose
>> to modify Best such that when a set of forecast runs is
>> combined, the
>> forecasts included from a run will be consecutive in time. This
>> implies
>> that any missing forecasts within a run will not be filled by a
>> previous
>> run; however, an older forecast can be used to fill in gaps when a
>> collection is missing entire run(s). This behavior ensures that
>> the Best
>> time series will no longer alternate repeatedly between different
>> forecast solutions, but rather only jump once from one set of
>> forecasts
>> (model run) to another.
>>
>> To address the second issue, we propose an additional
>> modification to
>> Best such that only 0 hour Forecasts are used to make up Best,
>> and not
>> Analysis fields. Additionally, we propose to add two more virtual
>> datasets: Analysis and Complete. Analysis will contain the
>> collection of
>> all analysis fields from the grib collection. Complete behaves
>> just as
>> Best currently does, containing every possible time, using the
>> smallest
>> forecast offset. In this case, the forecasts included from a run
>> will
>> not be guaranteed to be be consecutive in time, as they could be
>> mixed
>> between various runs as long as the smallest forecast offset
>> condition
>> is met.Â
>>
>> We are seeking comments on these solutions to see if they
>> represent a
>> useful set of features given the problems outlined above.
>>
>> Thanks!
>>
>> The TDS development team
>>
>>
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>>
>>
>> --
>> Don Murray
>> NOAA/ESRL/PSD and CU-CIRES
>> 303-497-3596 <tel:303-497-3596>
>> http://www.esrl.noaa.gov/psd/__people/don.murray/
>> <http://www.esrl.noaa.gov/psd/people/don.murray/>
>>
>> _________________________________________________
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>>
>>
> --
> Don Murray
> NOAA/ESRL/PSD and CU-CIRES
> 303-497-3596
> http://www.esrl.noaa.gov/psd/people/don.murray/
>
