Excerpt taken from: WMO No. 386 Manual on the Global Telecommunication System
|T1T2||Data type and/or form designators.|
|A1A2||Geographical and/or data type and/or time designators.|
It shall be a number with two digits. When an originator or compiler of bulletins issues two or more bulletins with the same T1T2A1A2 and CCCC the ii shall be used to differentiate the bulletins and will
be unique to each bulletin.
Alphanumeric bulletins containing reports prepared at the main synoptic hours for the stations included in the Regional Basic Synoptic Networks or stations included in the Regional Basic Climatological Networks shall be compiled into bulletins with ii in the series 01 to 19. This does not apply to bulletins compiled in CREX code.
Alphanumeric bulletins containing “additional” data as defined in Resolution 40 (Cg-XII) shall be compiled into bulletins with ii above 19. This does not apply to bulletins compiled in CREX code.
For bulletins compiled in GRIB, BUFR or CREX code or containing pictorial information, the use of ii is defined in the tables contained in Attachment II-5. Originators or compilers of bulletins shall use the ii values from these tables when they are defi ned for the purpose for which a bulletin is being intended.
For all bulletins ii shall only be used to designate “additional” data as defined in Resolution 40 (Cg-XII) if the same heading is never used for essential data and it complies with all the requirements above. If this is not the case, a unique CCCC shall be used as described below.
International four-letter location indicator of the station or centre originating or compiling the bulletin, as agreed internationally, and published in WMO-No. 9, Volume C1, Catalogue of Meteorological Bulletins.
In order to differentiate sets of bulletins that cannot be distinguished using the T1T2A1A2ii locations, a centre may establish additional CCCCs where the final two characters differ from its original CCCC. The two first letters of any additional CCCCs established by a centre shall remain the same as the original CCCC. For instance, the additional CCCCs could be used to indicate different satellites, different models or to differentiate between bulletins containing “additional” or “essential” data as defined in Resolution 40 (Cg-XII)). All CCCCs established by any centre shall be published and defined in Publication No. 9, Volume C1, Catalogue of Meteorological Bulletins.
Once a bulletin has been originated or compiled, the CCCC must not be changed. If the contents of a bulletin is changed or recompiled for any reason, the CCCC should be changed to indicate the centre or station making the change.
|YYGGgg||International date-time group.|
|YY||Day of the month.|
For bulletins containing meteorological reports intended for standard times of observation, the time shall be the standard time of observation in UTC.
For aerodrome, route and area (aeronautical) forecasts: the full hour in UTC (the last two digits shall be 00) preceding the transmission time.
For other forecasts and analyses: standard time of observation in UTC on which forecast or analysis is based.
For other messages the time shall be the time of compilation in UTC.
An abbreviated heading defined by T1T2A1A2 ii CCCC YYGGgg shall be used only once. Consequently, if this abbreviated heading has to be used again for an addition, a correction or an amendment, it shall be mandatory to add an appropriate BBB indicator, identifi ed by a three-letter indicator which shall be added after the date-time group.
The BBB indicator shall have the following forms:
where x is an alphabetic character of A through as described in Attachment II-12;
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