16 citations · 25 across the 18 of their papers we have counts for
18 papers
Numerical comparison of energy- versus circulation-preserving stochastic vortex dynamics
Sagy Ephrati, Darryl D. Holm
We compare two geometric stochastic frameworks for the two-dimensional Euler equations, being the circulation-preserving stochastic advection by Lie transport (SALT) and the energy…
Minimum-enstrophy solutions in topographic quasi-geostrophic flow on the rotating sphere
Sagy Ephrati, Erik Jansson
The minimum-enstrophy theory of Bretherton and Haidvogel postulates that two-dimensional turbulent systems evolve to a state that minimises enstrophy at a fixed energy level. We ex…
Diffusive behavior of transport noise on
Sagy Ephrati, Erik Jansson, Andrea Papini
We investigate theoretically and numerically transport noise-induced diffusion in flows on the sphere. Previous analysis on the torus demonstrated that suitably chosen transport no…
Trajectory learning for ensemble forecasts via the continuous ranked probability score: a Lorenz '96 case study
Sagy Ephrati, James Woodfield
This paper demonstrates the feasibility of trajectory learning for ensemble forecasts by employing the continuous ranked probability score (CRPS) as a loss function. Using the two-…
Thermal quasi-geostrophic model on the sphere: derivation and structure-preserving simulation
Michael Roop, Sagy Ephrati
We derive the global model of thermal quasi-geostrophy on the sphere via asymptotic expansion of the thermal rotating shallow water equations. The model does not rely on the asympt…
On spectral scaling laws for averaged turbulence on the sphere
Sagy Ephrati, Erik Jansson, Klas Modin
Spectral analysis for a class of Lagrangian-averaged Navier--Stokes (LANS) equations on the sphere is carried out. The equations arise from the Navier--Stokes equations by applying…
Critical latitude in global quasi-geostrophic flow on a rotating sphere
Arnout Franken, Erwin Luesink, Sagy Ephrati +1
In this paper, we study geostrophic turbulence without external forcing or dissipation, using a Casimir-preserving numerical method. The research examines the formation of large zo…
Casimir preserving numerical method for global multilayer geostrophic turbulence
Arnout Franken, Erwin Luesink, Sagy Ephrati +1
Accurate long-term predictions of large-scale flow features on planets are crucial for understanding global atmospheric and oceanic systems, necessitating the development of numeri…
An exponential map free implicit midpoint method for stochastic Lie-Poisson systems
Sagy Ephrati, Erik Jansson, Annika Lang +1
An integrator for a class of stochastic Lie-Poisson systems driven by Stratonovich noise is developed. The integrator is suited for Lie-Poisson systems that also admit an isospectr…
Probabilistic data-driven turbulence closure modeling by assimilating statistics
Sagy Ephrati
A framework for deriving probabilistic data-driven closure models is proposed for coarse-grained numerical simulations of turbulence in statistically stationary state. The approach…
Geometric derivation and structure-preserving simulation of quasi-geostrophy on the sphere
Erwin Luesink, Arnout Franken, Sagy Ephrati +1
We present a geometric derivation of the quasi-geostrophic equations on the sphere, starting from the rotating shallow water equations. We utilise perturbation series methods in vo…
A continuous data assimilation closure for modeling statistically steady turbulence in large-eddy simulation
Sagy Ephrati, Arnout Franken, Erwin Luesink +2
A closure model is presented for large-eddy simulation (LES) based on the three-dimensional variational data assimilation algorithm. The approach aims at reconstructing high-fideli…
Data-driven spectral turbulence modeling for Rayleigh-Bénard convection
Sagy Ephrati, Paolo Cifani, Bernard Geurts
A data-driven turbulence model for coarse-grained numerical simulations of two-dimensional Rayleigh-Bénard convection is proposed. The model starts from high-fidelity data and is b…
Data-driven stochastic spectral modeling for coarsening of the two-dimensional Euler equations on the sphere
Sagy Ephrati, Paolo Cifani, Milo Viviani +1
A resolution-independent data-driven stochastic parametrization method for subgrid-scale processes in coarsened fluid descriptions is proposed. The method enables the inclusion of…
Sparse-stochastic model reduction for 2D Euler equations
Paolo Cifani, Sagy Ephrati, Milo Viviani
The 2D Euler equations are a simple but rich set of non-linear PDEs that describe the evolution of an ideal inviscid fluid, for which one dimension is negligible. Solving numerical…
Data-driven stochastic Lie transport modelling of the 2D Euler equations
Sagy Ephrati, Paolo Cifani, Erwin Luesink +1
In this paper, we propose and assess several stochastic parametrizations for data-driven modelling of the two-dimensional Euler equations using coarse-grid SPDEs. The framework of…
Casimir preserving stochastic Lie-Poisson integrators
Erwin Luesink, Sagy Ephrati, Paolo Cifani +1
Casimir preserving integrators for stochastic Lie-Poisson equations with Stratonovich noise are developed extending Runge-Kutta Munthe-Kaas methods. The underlying Lie-Poisson stru…
Computational modeling for high-fidelity coarsening of shallow water equations based on subgrid data
Sagy Ephrati, Erwin Luesink, Golo Wimmer +2
Small-scale features of shallow water flow obtained from direct numerical simulation (DNS) with two different computational codes for the shallow water equations are gathered offli…