Laurent Bessières

Global tidal residual mean circulation: does it affect a climate OGCM?

A global description of the ocean tidal residual mean circulation (TRMC) is provided and its effect on a global ocean climate model is evaluated. The TRMC is computed from a global barotropic tidal model based on pure hydrodynamical equations and forced by the major tidal constituents. It thus includes both Stokes drift and non-linear tidal dynamics. The TRMC map exhibits remarkable basin scale structures in the Indonesian archipelago-Australian region and on the Malvinas shelf. Regions of largest transport are characterized by sites of high tidal amplitudes, abrupt topography and western boundaries. Yet transport magnitudes remain at a few tenths of a Sverdrup. This TRMC is introduced as an external forcing in an ocean climate model. At equilibrium, the thermohaline structure and the poleward heat transport of the ocean are almost insensitive to the TRMC. It is concluded that the TRMC is negligible for climate purposes in an ocean climate model.

Ricci flow on open 3–manifolds and positive scalar curvature

We show that an orientable 3-dimensional manifold M admits a complete riemannian metric of bounded geometry and uniformly positive scalar curvature if and only if there exists a finite collection F of spherical space-forms such that M is a (possibly infinite) connected sum where each summand is diffeomorphic toS 2 � S 1 or to some member of F. This result generalises G. Perelman’s classification theorem for compact 3-manifolds of positive scalar curvature. The main tool is a variant of Perelman’s surgery construction for Ricci flow.

Intrinsic and Atmospherically Forced Variability of the AMOC: Insights from a Large-Ensemble Ocean Hindcast

AbstractThis study investigates the origin and features of interannual-to-decadal AMOC variability from several ocean simulations, including a large (50-member) ensemble of global, eddy-permitting (1/4°) ocean/sea-ice hindcasts. After an initial stochastic perturbation, each member is driven by the same realistic atmospheric forcing over 1960-2015. The magnitude, spatio-temporal scales and patterns of both the atmospherically-forced and intrinsic/chaotic interannual AMOC variability are then characterised from the ensemble mean and ensemble spread, respectively. The analysis of the ensemble-mean variability shows that the AMOC fluctuations north of 40°N are largely driven by the atmospheric variability, which forces meridionally-coherent fluctuations reaching decadal time-scales. The amplitude of the intrinsic interannual AMOC variability never exceeds the atmospherically-forced contribution in the Atlantic basin, but it reaches up to 100% of the latter around 35°S, and 60% in the northern mid-latitudes. ...

Differentiable rigidity under Ricci curvature lower bound

In this article we prove a differentiable rigidity result. Let

Long time behaviour of Ricci flow on open 3-manifolds

(Y, g)

On the transformation of Pacific Water into Indonesian Throughflow Water by internal tidal mixing

and

Geometrisation of 3-manifolds

(X, g_0)

Collapsing irreducible 3-manifolds with nontrivial fundamental group

be two closed

Weak collapsing and geometrisation of aspherical 3-manifolds

n

Un théorème de rigidité différentielle

-dimensional Riemannian manifolds (