Annick Pouquet
LASP

Biography

Annick Pouquet defended her PhD in astrophysics in Nice in December 1976 and has been a scientist in Nice (OCA) and Boulder (today, NCAR as Emerita & LASP as part-time researcher). She was the director of several laboratories and programs over the years and held several administrative jobs for the community. She has developed new tools at the forefront of theory and high-performance computing and has 200+ publications and 10900+ citations. She was elected fellow of the American Physical Society (2004) and of AGU (2023). She received the Alfvén Prize (EPS) in 2020 and the Richardson Medal (EGU) in 2024. She was a guest Editor for a Wiley journal on Past and Future of Nonlinear Geophysics and is a Divisional Associate Editor for PRL until 2026, as well as co-editing other scientific journals. She also co-organized international meetings and gave invited lectures worldwide in laboratories and in conferences, and graduate classes locally and at international schools (Aspen, Les Houches, …).

She has performed inter-disciplinary research and education on multi-scale interactions in geophysical fluid dynamics, with applications to the atmosphere, the ocean, and the magnetospheric, solar and interstellar environments. An understanding of such interactions is at the root of lifting many obstacles in weather and climate modeling, and in the prediction of extreme events as tornadoes, hurricanes or coronal mass ejections. She works today on the multi-scale interplay between nonlinear eddies and waves leading to intermittent dissipation for neutral fluids with gravity and/or rotation, without or with magnetic fields.

Abstract: Strong dissipation in turbulence: waves and structures

Many flows in the laboratory and in Nature support waves and are also turbulent and thus difficult to characterize, model and predict. Fluids and plasmas for which the dissipative time based on viscosity is much longer than the time-scale of vortices (i.e. at large Reynolds numbers) need a way to dissipate the energy injected in the system, say by the Sun or the wind for the atmosphere and the oceans. Turbulence provides such a mechanism through numerous nonlinear mode coupling and the systematic formation of strong localized (intermittent) small-scale gradients, for instance in the form of current, vorticity and shear structures competing with inertial, gravity or Alfvén waves. It is in these structures that energy dissipation can occur, in a complex interplay between the large scales and the small intense scales at the origin of intermittency (see Figure 1).
Thus, why and how dissipation takes place physically in hydrodynamics, magnetohydrodynamic (MHD) and in other turbulent nonlinear systems as in the solar wind, the sun, the interstellar medium and beyond, is briefly presented, starting from basic considerations relying on simple models. The role of waves – such as those due to gravity, rotation or magnetic fields – is then analyzed in this context in terms of one governing parameter, namely the ratio of the wave period to the turbulent eddy (turn-over) time. It is shown that the spatially localized dissipation in such systems can be, in some cases and by some measure, stronger than for homogeneous isotropic turbulence in the absence of waves. This is associated with the occurrence of non-Gaussian probability distribution functions (PDFs) for various fields. The intermittency of strong localized structures is then analyzed in more detail through the joint behavior of normalized third and fourth-order moments (namely skewness S and kurtosis K) of the PDFs of these fields (see Rosenberg et al., 2023 Atmosphere 15 and references therein), noting that S = 0, K = 3 for a Gaussian. Parabolic K(S) ∼ S² relations are observed in many instances, possibly justified through a Langevin model with additive and multiplicative noise, as already proposed for the sea-surface temperature of the ocean, the planetary boundary layer, the climate, as well as for fusion plasmas, the magnetosphere, the solar wind and dwarf galaxies. Is this a universal key to characterize turbulence properties?