NetCDF time coordinate
From BAWiki
Contents
Introduction
Date, time and calendar plus (optional) use of time intervals.
Time information in a netCDF file
Dimensions
dimensions:
- time = number of time steps or UNLIMITED;
- bnd = 2 ;
Comment: In case the number of time steps is known before-hand, Bert Jagers (Deltares) recommends to use a fixed length instead of an UNLIMITED dimension due to performace reasons. But this only works for variables not exceeding 4 GiB.
Variables
Coordinate time
double time(time) ;
- time:standard_name = "time" ;
- time:long_name = "time" ;
- time:units = "time units since YYYY-MM-DD hh:mm:ss zone" ;
- time:axis = "T"
- time:calendar = "gregorian"
- time:bounds = "timebnd"
Comment:
- For time units the following units are common:
- seconds,
- minutes,
- hours, and
- days.
- Specification of zone is optional (default is UTC). Some examples for other time zones:
- zone = +1:00 for CET (Central European Time), or
- zone = +2:00 for CEST (Central European Summer Time).
- Attribute bounds must be specified, in case (some) data are e.g. mean or integral (sum) values with respect to time. Examples: Daily mean temperature, daily rainfall. These data must possess attribute cell_methods with e.g. "time: mean" or "time: sum". See also CF Conventions "cell_methods".
Time intervals
double timebnd(time,bnd) ;
Comment:
- timebnd(n,1) is equivalent to the lower bound for the n-th time step.
- timebnd(n,2) is equivalent to the upper bound for the n-th time step.
- Subsequent intervals may not be continous.
- For continuous intervals timebnd(n,2) == timebnd(n+1,1) holds.
Remarks
- A double precision variable should be used for time to guarantee sufficient accuracy..
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