I have often wondered about the following question. Never received a
confident answer from anyone, can  anyone enlighten me?

What is the real time on the models?  E.G., Is 12Z LAPS  really for 12z
(11pm AEDST), and if so, why, when the inputs are based on 10Z data? And
wouldnt it be easier if output steps were for 9pm, 12 pm, 3 pm etc?
 

From Paul Stewart

RE: BASE TIMES IN NMOC'S OPERATIONAL NWP SYSTEMS

Dear Colleagues,

The following is an attempt to answer Bob Moore's query as to "What is the real
time on the models?"

The times for the various operational NWP systems in NMOC are still based on 11
and 23 UTC (and also 05 and 17UTC).

However, this does not mean that only observational data for these specific
times are used. The current operational assimilation schemes (LAPS, TLAPS,
including TC_LAPS, and GASP) use 6-hourly data insertions. This effectively
means that 6 hours of observational data is used in generating an analysis at a
given time (ie at 05, 11, 17 or 23 UTC).

Currently for a given analysis time, the time window used is from -2 to +4
hours. Thus, for example, observations from 09 UTC to 15 UTC are used in the
analysis for 11 UTC. (It is further noted that the observations, within the 6
hour window, are effectively weighted according to their time difference from
the nominal analysis time.)

Over the years, a number of changes have been implemented with the aim of
eventually using the base times: 00, 06, 12 and 18 UTC consistently throughout
the operational system in NMOC. These have included:

. the adjustment of chart labels so that base times for analyses were rounded
off to 00, 06, 12 and 18 UTC and valid forecast times adjusted accordingly;

. the use of 00, 06, 12 and 18 UTC in the actual data set names within the real
time data base (which were introduced for GASP several years ago and have, just
in the last few months, been used for the various LAPS systems).

However, the observational extraction procedure and the internal files
(including those in NetCDF form), used within the operational NWP systems, still
have base times of 05, 11, 17 and 23 UTC.

It is only when these latter procedures and file structures are changed that we
can say that the base times are 00, 06, 12 and 18 UTC. (It is planned that this
will happen during 2002.)
 

Hopefully this may be of some use.

With best wishes for the New Year,

Paul Stewart
NMOC