Noé Lahaye

National Institute for Research in Computer Science and Control | INRIA · FLUMINANCE - Fluid Flow Analysis, Description and Control from Image Sequences Research Team

Abstract In this work, a stochastic representation based on a physical transport principle is proposed to account for mesoscale eddy effects on the large‐scale oceanic circulation. This stochastic framework arises from a decomposition of the Lagrangian velocity into a smooth‐in‐time component and a highly oscillating noise term. One important chara...

In this work, a stochastic representation based on a physical transport principle is proposed to account for mesoscale eddy effects on the large-scale oceanic circulation. This stochastic framework arises from a decomposition of the Lagrangian velocity into a smooth-in-time component and a highly oscillating noise term. One important characteristic...

A class of exact solutions of the magnetohydrodynamic quasi-geostrophic equations (MQG), which result from rotating shallow water magnetohydrodynamics in the limit of small Rossby and magnetic Rossby numbers is constructed analytically. These solutions are magnetic modons, steady-moving dipolar vortices, which are generalizations of the well-known...

The Lagrangian and Eulerian surface current signatures of a low-mode internal tide propagating through a turbulent balanced flow are compared in idealized numerical simulations. Lagrangian and Eulerian total (i.e. coherent plus incoherent) tidal amplitudes are found to be similar. Compared to Eulerian diagnostics, the Lagrangian tidal signal is mor...

Wide‐swath altimetry, for example, the Surface Water and Ocean Topography mission is expected to provide Sea Surface Height (SSH) measurements resolving scales of a few tens of kilometers. Over a large fraction of the globe, the SSH signal at these scales is essentially a superposition of a component due to balanced motions (BMs) and another compon...

The instability of surface lenticular vortices is investigated using a comprehensive suite of laboratory experiments combined with numerical linear stability analysis as well as nonlinear numerical simulations in a two-layer Rotating Shallow Water model. The development of instabilities is discussed and compared between the different methods. The l...

The future wide‐swath satellite altimeters, such as the upcoming Surface Water Ocean Topography (SWOT) mission, will provide instantaneous 2D measurements of sea level down to the spatial scale of O(10 km) for the first time. However, the validity of the geostrophic assumption for estimating surface currents from these instantaneous maps is not kno...

Internal tides are a predominant source of high‐frequency variability and diapycnal mixing in the ocean. Understanding their dynamics and lifecycle is necessary to better understand their role in the ocean circulation. In this paper, we describe and quantify internal tide generation, propagation and dissipation in a sector of the North Mid‐Atlantic...

The generation of lee waves in the Gulf Stream along the U.S. seaboard is investigated using high resolution realistic simulations. The model reproduces the surface signature of the waves, which compares favourably with observations from satellite sun glitter images in the region. In particular, a large number of internal waves are observed above t...

Coupled-mode equations describing the propagation and scattering of internal waves over large amplitude arbitrary topography in a two-dimensional stratified fluid are derived. They consist of a simple set of ordinary differential equations describing the evolution of modal amplitudes, based on an orthogonality condition that allows one to distingui...

Over mid-ocean ridges, the interaction between the currents and the topography gives rise to complex flows, which drive the transport properties of biogeochemical constituents, and especially those associated with hydrothermal vents, thus impacting associated ecosystems. This paper describes the circulation in the rift valley along the Azores secto...

The upper ocean is energetic at scales below the Rossby deformation radius owing to the existence of internal waves and submesoscale fronts and vortices. These contribute significantly to energy dissipation, tracer mixing and exchanges between the ocean surface layer, the ocean interior, and the atmospheric boundary layer. Internal waves and submes...

A specific instability of vortices is found in rotating shallow water equations with horizontal density/temperature gradients, which is used for modelling atmospheric and oceanic mixed layers. The model is re-interpreted as dynamics of rotating non-isentropic two-dimensional gas. The instability, which was not reported previously, develops in a way...

Instabilities of hurricane-like vortices are studied with the help of a rotating shallow-water model, including the effects of moist convection. Linear stability analysis demonstrates that dominant unstable modes are mixed Rossby-inertia-gravity waves. It is shown that, depending on fine details of the vorticity profile, a wavenumber selection of t...

Instabilities of isolated anticyclonic vortices in the two-layer rotating shallow water model are studied at Rossby numbers up to two, with the main goal to understand the interplay between the classical centrifugal instability and other ageostrophic instabilities. We find that different types of instabilities with low azimuthal wavenumbers exist,...

Coherent structures are ubiquitous features of atmospheric and oceanic flows. The corresponding meso- and large scale circulation is in geostrophic equilibrium. However, at larger Rossby numbers, ageostrophic effects may push the structures away from this equilibrium, and new types of instabilities can also disturb their dynamics. In this thesis, t...

Coherent structures are ubiquitous features of atmospheric and oceanic flows. The cor- responding meso- and large scale circulation is in geostrophic equilibrium. However, at larger Rossby numbers, ageostrophic effects may push the structures away from this equi- librium, and new types of instabilities can also disturb their dynamics. In this thesi...

We report results of direct numerical simulations of decaying turbulence in an inviscid rotating shallow water model. We use a new-generation high-resolution well-balanced shock-capturing finite-volume scheme with several types of initializations: “classical” ones with random velocity and/or height fields, or an initialization with randomly oriente...

We study formation and properties of new coherent structures: ageostrophic modons in the two-layer rotating shallow water model. The ageostrophic modons are obtained by ‘ageostrophic adjustment’ of the exact modon solutions of the two-layer quasi-geostrophic equations with the free surface, which are used to initialize the full two-layer shallow wa...

We show that a new type of coherent structure, a shock modon, exists in a rotating shallow water model at large Rossby numbers. It is a combination of an asymmetric vortex dipole with a stationary hydraulic jump. The structure is long living, despite the energy dissipation by the hydraulic jump, and moving along a circular path. Collisions of shock...

We study collisions of recently discovered ageostrophic modons in rotating shallow water model at different values of impact parameter and find that two new types of coherent vortex structures may be formed during this process: “nonlinear” modons, i.e., coherent dipoles with essentially nonlinear scatter plot and coherent tripoles. Both are known f...