# tide start

tide_start
tide_start
Reference time origin for tidal forcing. This is the time used when processing input tidal model data. It is needed in routine set_tides.F to compute the correct phase lag with respect ROMS/TOMS initialization time.
option =
units = days
routine = mod_scalars.F
keyword = TIDE_START
input = ocean.in

If the time origin for the harmonic tidal constituents is not the same as the time origin used internally by ROMS then the tidal phase will be in error. To accommodate this possibility, the parameter tide_start in units of days can be used to make the appropriate shift to the phase of the harmonic tidal forcing. The value set in ocean.in.

The parameter is used in routine set_tides.F after conversion into seconds:

For example, if the date corresponding to in ROMS is 1-Jan-2006, i.e. ocean_time has the netcdf units attribute "days since 2006-01-01 00:00:00", but the harmonic forcing data was computed assuming a base date for time of 2005-01-01 00:00:00, then set the value in your ocean.in with

```     TIDE_START = -365.0d0              ! days
```

Note that TIDE_START will typically be negative for tide harmonic reference times that predate the model time origin.

The value of DSTART does not affect how the user sets tide_start.

Tidal forcing is activated by CPP options SSH_TIDES and UV_TIDES and requires a tide harmonic forcing netcdf file.