Time stepping

Time stepper refers to the means by which a simulation is advanced in time. The configuration of a simulation is set by the TimeIntegration section of the Omega configuration file:

  TimeIntegration:
    CalendarType: No Leap
    TimeStepper: Forward-Backward
    TimeStep: 0000_00:10:00
    StartTime: 0001-01-01_00:00:00
    StopTime: 0001-01-01_02:00:00
    RunDuration: none

This configuration refers to the default time stepping used for the model dynamics (momentum and continuity equations). Additional time steppers can be used for other portions of the model (eg the barotropic mode or tracer transport) that may have different time steps and use different algorithms.

The Calendar choice is describe in the Time Management section.

The TimeStepper option refers to the numerical scheme used to advance the model in time. Omega implements a number of time-stepping schemes. The user can select the scheme they want in the configuration file. The following time steppers are currently available:

Config option name	Scheme
Forward-Backward	forward-backward
RungeKutta2	second-order two-stage midpoint Runge Kutta method
RungeKutta4	classic fourth-order four-stage Runge Kutta method

The time step refers to the main model time step used to advance the solution forward. The format is in dddd_hh:mm:ss for days, hours, minutes and seconds.

The StartTime refers to the starting time for the simulation. It is in the format yyyy-mm-day_hh:mm:ss for year, month, day, hour, minute, second. This refers to the initial start time; for a longer simulation, the current time will be modified by the restart file to update to the present time for the current segment of the simulation.

The simulation will be stopped either at a fixed StopTime if provided or by the RunDuration. For shorter simulations, the StopTime can be used to specify a specific time to stop. For longer simulations with multiple segments that are restarted, the RunDuration should used and should be set to fit within the queue time. The format for StopTime is the same as StartTime. The format for RunDuration is the same as the TimeStep.

Only one of the StopTime or RunDuration should be specified with the other set to either an empty string or “none”. If both are specified, the RunDuration is used instead of the StopTime.