Setting time parameters without tidal reference times

[SophieWard]

Hi all,

I’m setting up a shelf-scale ROMS application. I’m using tidal forcing on the boundaries; however the tidal ‘data’ are output from a global model, rather than from a tidal database. The reason behind using these data is the fact that I’ll also be setting up palaeotidal model runs and so the model will need to be forced using palaeotides.

I’m struggling with getting the timing correct, since I don’t have tidal reference times and hence D_START, TIDE_START AND TIME_REF are all somewhat obsolete in my case…I’ve tried a number of different combinations of values of time parameters in the ocean.in file, the latest being:

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  DSTART =  0.0d0                     ! days
  TIDE_START =  0.0d0                      ! days
  TIME_REF = 0.0d0               ! yyyymmdd.dd

Although I don’t think this is a problem as such, problems do arise when I try to set the times in the ocean_bry.nc file. What should tstart, tend, bry_time (and hence length(time)) be considering I don’t have a reference time?

I know that Tmin and Tmax are set by get_cycle.F but this routine obviously doesn’t agree with my data. I’ve tried a variety of values for the time vector in the boundary file, all of which give the same kind of errors:

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NL ROMS/TOMS: started time-stepping: (Grid: 01 TimeSteps: 00000001 - 00010800)
    GET_NGFLD   - 3D u-momentum western boundary condition,  t = ***** **:**:**
                   (Rec=0001, Index=1, File: ocean_bry.nc)
                   (Tmin=          0.0000 Tmax=          0.0000)

(and so on for each of the netcdf variables in my ocean_bry file). And then it says:

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 SET_NGFLD  - current model time exceeds ending value for variable: u_west
              TDAYS     =          0.0000
              Data Tmin =          0.0000  Data Tmax =          0.0000
              Data Tstr =          0.0000  Data Tend =          0.0000
              TINTRP1   = ***************  TINTRP2   = ***************
              FAC1      = ***************  FAC2      = ***************

Any ideas about how I could get around this?

Thanks,
Sophie

[wilkin]

TIDE_START is going to be largely irrelevant in your case - especially the paleo case.

All this parameter does is shift the phase of the tide in the event that the harmonics are with respect to a different time=0 than your model. See the WikiROMS entry https://www.myroms.org/wiki/index.php/tide_start

If you are comparing to time series data in detail, an error in TIDE_START might cause high tide to occur at the wrong time of day, or spring tide in the wrong week, but in the long run the tide range and the attendant mixing would be the same.

For your climatological runs you can add the "cycle_length" attribute to the time dimension in the forcing file, and then ROMS will perpetually cycle the forcing data (there are some notes at http://www.myroms.org/index.php?page=forcing)

[SophieWard]

Thanks John

Very useful pointers. My time was already cyclical but it was the way I was defining the vector itself that was the key, I think...the time-related errors have gone (for now, at least).


Sophie