9 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…
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…
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…
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…