Tides

MOM6 can include tidal forcing at the open boundaries, by superimposing tidal variations onto the boundary condition SSH and velocity fields, and throughout the domain, by adding tidal forcing to the momentum equations.

Tidal variations in a field such as sea level can be represented as a sum over a series of harmonic constituents: $\zeta(t) = \sum_{c=1}^{n_c} f_c A_c \cos\left(\omega_c (t - t_0) + u_c + V_c - \phi_c \right)$.

In this equation,

• $f$ and $u$ are modulation of the amplitude and phase, respectively, by the 18.6 year nodal cycle.
• $A$ is the amplitude of the constituent.
• $\omega$ is the angular frequency of the constituent.
• $t$ is the current time and $t_0$ is some origin time.
• $V$ is the phase of the equilibrium tide at $t_0$ and along 0 degrees lon.
• $\phi$ is the phase lag of the local tide relative to the equilibrium tide at 0 degrees lon.

TIDE_REF_DATE

TIDE_REF_DATE sets the origin date used in the calculation of the tides ($t_0$). In most cases, it is an arbitrary date and can be set to any fixed value near the start of the model run. In less common cases where the phases in the tidal boundary condition data are specified relative to a certain date, TIDE_REF_DATE should be set to this date.

Example: TIDE_REF_DATE = 1993, 1, 1

TIDE_NODAL_REF_DATE

TIDE_NODAL_REF_DATE sets the date used to calculate the amplitude and phase modulation factors for the 18.6 year nodal variation of the tide. Generally, it is set to the middle of the current model year and is updated every time the model starts a new year using #override.

Recommended value: ${year},7,2.

TIDE_USE_EQ_PHASE

Includes the $V$ term in the calculation of the tidal forcing.

Recommended value: True