EGU21-10184
https://doi.org/10.5194/egusphere-egu21-10184
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Inverse energy cascade in ocean macroscopic turbulence:      Energy transfer rate ε and Richardson-Obhukov  constant g from an surface drifter experiment in the Benguela upwelling system

Julia Draeger-Dietel and Alexa Griesel
Julia Draeger-Dietel and Alexa Griesel
  • Universitaet Hamburg, Institute of Oceanography, Hamburg, Germany (julia.draeger-dietel@uni-hamburg.de)

We derive the energy transfer rate ε from the 3rd order relative (longitudinal)  velocity structure function <Δul3>=(3/2)εs from ocean surface drifter trajectories in the turbulent mixed layer of the Benguela upwelling region off the coast of Namibia.  Combination with the  mean squared pair separation<s2(t)> =gεt3 reveals the Richardson-Obhukov constant g≅0.5, which is remarkably close to the one measured in  controlled two-dimensional turbulent flows in laboratory. We verify the  two coupled  cascades of energy (upscale/inverse) and enstrophy (downwscale) by  the  theoretically predicted  slope 1  for <Δul3> for inertial scales (above the injection scale) and slope 2 for  the 2nd order structure function <Δul2> for non-local scales (below the injection scale) respectively. We detect  additional 'ballistic contributions' in the central regime of the corresponding probability distribution P(st) of relative separations s for fixed time t, leading to an additional  power law factor s with  α ≅ 5/3. The algebraic decay with 1<α <2 revives  to the relevance of Levy distributions in the stochastic description of the turbulent transport process in contrast to former claims. Our findings  of a positively skewed   probability distribution P(Δuls) of relative longitudinal velocity Δul  for inertial scales s renews the question of intermittency in the  inverse energy cascade.

How to cite: Draeger-Dietel, J. and Griesel, A.: Inverse energy cascade in ocean macroscopic turbulence:      Energy transfer rate ε and Richardson-Obhukov  constant g from an surface drifter experiment in the Benguela upwelling system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10184, https://doi.org/10.5194/egusphere-egu21-10184, 2021.

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