Hi John,
from the EC and Norwegian models I usually use, the grib reference time
is usually equivalent to the forecast_reference_time. 'run time' does
not work so well for our models. We usually have some hours model
warm-up (analysis) and then, usually at the forecast_reference_time, we
switch to forecast-mode. When translating those to netcdf, I try to put
negative 'run times' for analysis, and positive for forecasts, derived
from octed 20 in PDS (end-time) - I'm not sure if this fits with your
definition of run-time.
Accumulation-period should be defined by start-time and end-time (octet
19/20/21 in PDS), but more often than not, it is just defined in the
parameter (i.e. accumulated_precipitation) and one has to guess the
accumulation period.
It really gets messy when looking at special deliveries to other
institutions which aren't used to reference-times. Some of them require
each run-time to be encoded in octed 13-17 (PDS). Grib2 is less used, so
I haven't seen these artifacts there yet, it might be that in this case,
3: Observation time, should be used?
Heiko
On 2013-11-22 19:03, John Caron wrote:
The question is whether the CDM can assume that GRIB "Reference time of data" is the
"run time" of a forecast model.
In GRIB-1 docs, in the PDS there is:
"Reference time of data – date and time of start of averaging or accumulation
period"
In GRIB-2 in Identification section, there is:
12 Significance of reference time (see Code table 1.2)
Reference time of data:
13–14 Year (4 digits)
15 Month
16 Day
17 Hour
18 Minute
19 Second
And Code table 1.2 has the following:
Code Table Code table 1.2 - Significance of reference time (1.2)
0: Analysis
1: Start of forecast
2: Verifying time of forecast
3: Observation time
-1: Reserved
-1: Reserved for local use
255: Missing
None of this obviously refers to "run time", although I suspect that's how many
centers use it. However, it appears that when you want to define a time interval, say
"average of the temperature, starting 12 hours and ending 24 hours from reference, you
may use the reference time to define the start of that interval. In which case, its not the
runtime. Im hoping thats not the case, that reference time is the same as the run time for
forecast models.
So if you know how to interpret these for any or all datasets, please send me a
note, or post to this group. Please pass this question on to anyone who might
be willing to contribute.
Thanks!
John
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