TY - JOUR

T1 - Order out of Chaos

T2 - Slowly Reversing Mean Flows Emerge from Turbulently Generated Internal Waves

AU - Couston, Louis Alexandre

AU - Lecoanet, Daniel

AU - Favier, Benjamin

AU - Le Bars, Michael

N1 - Funding Information:
The authors acknowledge funding by the European Research Council under the European Union’s Horizon 2020 research and innovation program through Grant No. 681835-FLUDYCO-ERC-2015-CoG. D. L. is supported by a PCTS fellowship and a Lyman Spitzer Jr fellowship. LAC thanks Bruno Ribstein for useful discussions and references on parametrizations in General Circulation Models. Computations were conducted with support by the HPC resources of GENCI-IDRIS (Grant No. A0020407543 and A0040407543) and by the NASA High End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center on Pleiades with allocations GID s1647 and s1439.
Publisher Copyright:
© 2018 American Physical Society.

PY - 2018/6/15

Y1 - 2018/6/15

N2 - We demonstrate via direct numerical simulations that a periodic, oscillating mean flow spontaneously develops from turbulently generated internal waves. We consider a minimal physical model where the fluid self-organizes in a convective layer adjacent to a stably stratified one. Internal waves are excited by turbulent convective motions, then nonlinearly interact to produce a mean flow reversing on timescales much longer than the waves' period. Our results demonstrate for the first time that the three-scale dynamics due to convection, waves, and mean flow is generic and hence can occur in many astrophysical and geophysical fluids. We discuss efforts to reproduce the mean flow in reduced models, where the turbulence is bypassed. We demonstrate that wave intermittency, resulting from the chaotic nature of convection, plays a key role in the mean-flow dynamics, which thus cannot be captured using only second-order statistics of the turbulent motions.

AB - We demonstrate via direct numerical simulations that a periodic, oscillating mean flow spontaneously develops from turbulently generated internal waves. We consider a minimal physical model where the fluid self-organizes in a convective layer adjacent to a stably stratified one. Internal waves are excited by turbulent convective motions, then nonlinearly interact to produce a mean flow reversing on timescales much longer than the waves' period. Our results demonstrate for the first time that the three-scale dynamics due to convection, waves, and mean flow is generic and hence can occur in many astrophysical and geophysical fluids. We discuss efforts to reproduce the mean flow in reduced models, where the turbulence is bypassed. We demonstrate that wave intermittency, resulting from the chaotic nature of convection, plays a key role in the mean-flow dynamics, which thus cannot be captured using only second-order statistics of the turbulent motions.

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U2 - 10.1103/PhysRevLett.120.244505

DO - 10.1103/PhysRevLett.120.244505

M3 - Article

C2 - 29957013

AN - SCOPUS:85048619430

VL - 120

JO - Physical Review Letters

JF - Physical Review Letters

SN - 0031-9007

IS - 24

M1 - 244505

ER -