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DY: Fachverband Dynamik und Statistische Physik

DY 4: Fluid Physics and Turbulence

DY 4.5: Vortrag

Montag, 18. März 2024, 10:45–11:00, BH-N 128

Dual energy cascade in ocean macroscopic turbulence: Kolmogorov self-similarity in surface drifter observations and Richardson-Obhukov constant — •Julia Dräger-Dietel and Alexa Griesel — Institut für Meereskunde, Universität Hamburg, Hamburg, Germany

We combine two point velocity and position data from surface drifter observations in the Benguela upwelling region off the coast of Namibia. The compensated third order longitudinal velocity structure function <u^3(s)>/s shows a positive plateau for inertial separations s roughly between 9 km and 120 km revealing an inverse energy cascade with energy transfer rate ε=1.2 10^-7 m^3/s^2. For scales roughly below 800 m a negative plateau for <u^3(s)>/s indicates to a direct energy cascade with energy-transfer rate 30 times smaller. For both regimes the second order longitudinal velocity structure function <u^2(s)> scales as s^(2/3), as theoretically predicted. Deviations from Gaussianity of the corresponding probability distributions are stronger for the direct cascade in accordeance with theoretical expectation, for instance the kurtosis is 3 times larger. The combination of the energy transfer rate ε with Richardson dispersion <s^2(t)>=g ε t^3, where <s^2(t)> is the mean squared pair separation at time t, reveals a Richardson-Obhukov constant of g=0.11 for the inverse cascade regime [1].

[1] Draeger-Dietel et al. https://arxiv.org/abs/2311.13560

Keywords: turbulence; geostrophic turbulence; Intermittency; ocean observations; anomalous diffusion