Stochastic interpretations of the oceanic primitive equations with relaxed hydrostatic assumptions

In this paper, we investigate how weakening the classical hydrostatic balance hypothesis impacts the well-posedness of the stochastic location uncertainty (LU) primitive equations. The models we consider are intermediate between the incompressible 3D LU Navier–Stokes equations and the LU primitive equations with standard hydrostatic balance. As such, they are expected to be numerically tractable, while accounting well for phenomena within the grey zone between hydrostatic balance and non-hydrostatic processes. Our main result is the well-posedness of a low-pass filtering-based stochastic interpretation of the LU primitive equations, with rigid-lid type boundary conditions, in the limit of “quasi-barotropic” flow. This assumption is linked to the structure assumption proposed by Agresti et al. (2024, 2025), which can be related to the dynamical regime where the primitive equations remain valid (Marshall et al. (1997)). Furthermore, we present and study two eddy-(hyper)viscosity-based models.