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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. >> >> 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 >> >> >> _________________________________________________ >> thredds mailing list >> thredds@xxxxxxxxxxxxxxxx <mailto:thredds@xxxxxxxxxxxxxxxx> >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/__mailing_lists/ >> <http://www.unidata.ucar.edu/mailing_lists/> >> >> >> -- >> 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/> >> >> _________________________________________________ >> thredds mailing list >> thredds@xxxxxxxxxxxxxxxx <mailto:thredds@xxxxxxxxxxxxxxxx> >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/__mailing_lists/ >> <http://www.unidata.ucar.edu/mailing_lists/> >> >> >> > -- > Don Murray > NOAA/ESRL/PSD and CU-CIRES > 303-497-3596 > http://www.esrl.noaa.gov/psd/people/don.murray/ >
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