Modelling projects in Biology, Ecology and Environment with Vincent Bansaye and Yann Le Poul.

Numerical modelling and satellite remote sensing with Hélène Chepfer (until 2012); see some slides here .

Water Hydrodynamics with Olivier Thual (until 2010)

Climate Dynamics with Hervé le Treut

Distributed and Parallel Computing with Éric Goubault and Sylvie Putot

Atmospheric and Oceanic Dynamics with Hervé le Treut ; see some slides here .

Experimental Projects in Geophysical Fluid dynamics with Alexandre Stegner

Fluid Mechanics with Patrick Huerre (until 2006)

Continuum Mechanics with Patrick le Tallec and formerly Jean Salençon (until 2005)

Since 2010 I lead an effort to re-design the dynamical core of LMD-Z, the global circulation model part of the IPSL Earth System model, with special care given to the consistency of the mass, energy, vorticity and angular momentum budgets, while extending the capabilities of the dynamical core beyond the hydrostatic primitive equations and latitude-longitude grids (DYNAMICO project).

Earlier work of mine deals with instabilities of the Ekman boundary layer and similar flows and multi-scale modelling of the atmosphere by various approaches, often involving eventually the numerical solution of idealized problems (TRANSTEK project).

Various funding opportunities exist through local and national programmes and already funded projects. Please get in touch with me.

Dynamical Core on Icosahedral Grid

LMDZ4, the current version of LMD-Z, has a shallow-atmosphere, hydrostatic dynamical core. It is based on a latitude-longitude C-grid, a hybrid pressure-based terrain-following vertical coordinate, second-order enstrophy-conserving finite-difference discretization and positive-definite advection. Grid refinement is implemented as a continuous zoom via smooth grid stretching. An extensive package of physical paramererizations is coupled to the dynamical core. IPSL-CM is currently used to produce AR5 simulations. LMD-Z is also at the heart of GCMs of planetary atmospheres (Mars, Venus and Titan).

It is well-known that the latitude-longitude coordinates have a strong singularity at the poles which is undesirable in terms of both numerical stability and computational efficiency. Regular tesselations of the sphere such as a recursively subdivided icosahedron provide an almost-uniform grid and a path to highly parallel computations based on domain decomposition. LMD's logo is itself an icosahedron, evoking the pioneering work of Robert Sadourny on the use of icosahedral grids for solving the equations of atmospheric motion.

The primary goal of DYNAMICO is to re-formulate in LMD-Z the horizontal advection and dynamics on a icosahedral grid, while preserving or improving their qualities with respect to accuracy, conservation laws and wave dispersion. In turn, a new grid refinement strategy is required. A broader goal is to revisit all fundamental features of the dynamical core, especially the shallow-atmosphere/traditional approximation, the vertical coordinate and the coupling with physics. Efficient implementation on present and future supercomputing architectures is also a key issue addressed by DYNAMICO.

DYNAMICO is currently able to solve the hydrostatic primitive
equations and participated to the DCMIP
workshop held in August 2012 at NCAR. In the near future we will
investigate its extension to deep-atmosphere and possibly
non-hydrostatic equations following a variational approach that
naturally conserves mass, energy and, in a somewhat restricted sense,
potential vorticity. If you are not afraid of
work-in-progress, you can browse our source code .

DYNAMICO is or has been supported by the
Indo-French Centre for the Promotion of Advanced Research and by
IPSL and by the
G8 Research Councils Initiative on Multilateral Research Funding,
project ICOMEX.

DYNAMICO publications :

T. Dubos and M. Tort ** (2014) **

Equations of atmospheric motion in non-Eulerian vertical coordinates :
vector-invariant form and Hamiltonian formulation

Mon. Wea. Rev. 142(10) : 3860-3880

M. Tort and T. Dubos ** (2014) **

Usual approximations to the equations of
atmospheric motion : a variational perspective

J. Atmos. Sci 71(7) : 2452-2466

Peter H. Lauritzen, P. A. Ullrich,
C. Jablonowski, P. A. Bosler, D. Calhoun, A. J. Conley, T. Enomoto,
L. Dong, S. Dubey, O. Guba, A. B. Hansen, E. Kaas, J. Kent,
J.-F. Lamarque, M. J. Prather, D. Reinert, V. V. Shashkin,
W. C. Skamarock, B. SÃ¸rensen, M. A. Taylor, and M. A. Tolstykh
** (2014) **

A standard test case suite for
two-dimensional linear transport on the sphere: results from a
collection of state-of-the-art schemes.

Geosci. Model Dev., 7, 105-145. doi:10.5194/gmd-7-105-2014.

Related publications :

M. Tort, T. Dubos and T. Melvin

Energy-conserving finite-difference schemes for quasi-hydrostatic equations.

submitted to Quart. J. Roy. Met. Soc.

M. Aechtner, N. Kevlahan and T. Dubos ** (accepted) **

A conservative adaptive wavelet method for the shallow water equations on the sphere.

Quart. J. Roy. Met. Soc.

J. Thuburn, C.J. Cotter, T. Dubos ** (2014) **

A mimetic, semi-implicit, forward-in-time,
finite volume shallow water model : comparison of
hexagonal-icosahedral and cubed sphere grids

Geophys. Mod. Dev. 7 (3) : 909-929

M. Tort, T. Dubos, V. Zeitlin and
F. Bouchut ** (2014) **

Consistent shallow-water equations on the rotating sphere with complete Coriolis force and topography

J. Fluid Mech. 748 : 789-821

M. Tort and T. Dubos ** (2014) **

Dynamically consistent shallow-atmosphere equations with a complete
Coriolis force

Quart. J. Roy. Met. Soc. 10.1002/qj.2274

21 - T. Dubos and N. Kevlahan,
**(2013) **

An adaptive wavelet method for the shallow-water equations on a staggered grid conserving mass and vorticity.

Quart. J. Roy. Met. Soc., 139: 1997-2020

14 - T. Dubos **(2009)**

A conservative Fourier-finite-element method for solving PDEs on the whole sphere.

Quart. J. Roy. Met. Soc. 135(644) 1877-1889

Transition and Turbulence in the Stratified Ekman Layer

In this project, we adopt a fluid dynamical approach aimed at elucidating the purely internal, dynamical mechanisms of turbulence intermittency in the SBL. The backbone of our approach is a thorough study of the transition to turbulence in the stratified Ekman layer, considered as a minimal model of the SBL. Our working hypothesis is that the secondary instability of stratified Ekman layer roll vortices can be a purely internal and dynamical source of intermittency, without invoking other causes that may be relevant depending on atmospheric conditions. Indeed if the time scale of secondary instability is dictated by local overturning, as suggested by stratified free shear layers, while the emergence of a roll vortex takes place within an advective time scale, the emergence/breakdown phases of the eddy life cycle become increasingly asymmetric as stratification increases, with shorter and shorter turbulent phases. TRANSTEK is supported by ANR contract ANR-09-JCJC-0108-01 and by LEFE/INSU.

Related publications :

M. Mathur, S. Ortiz, T. Dubos and J.-M. Chomaz

Effect of an axial flow on the centrifugal, elliptic and hyperbolic instabilities in Stuart vortices

J. Fluid Mech.

N. Mkhinini, T. Dubos and P. Drobinski, **(2013) **

On the nonlinear destabilization of a stratified shear flow

J. Fluid Mech. 731 : 443-460

N. Mkhinini, T. Dubos and P. Drobinski, **(2013) **

Secondary instability of the stratified Ekman layer

J. Fluid Mech. 728 : 29-57