2023/11/22 by Dräger-Dietel, J., Griesel, A.
#FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn)
paper · doi:10.48550/arxiv.2311.13560
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 ⟨Δuℓ\rm 3⟩/s shows a positive plateau for inertial separations s roughly between 9~\rmkm and 120~\rmkm revealing an inverse energy cascade with energy transfer rate ε≃ 1.2 ± 0.1 ⋅ 10-7 m3/s2. Deviations from Gaussianity of the corresponding probability distribution P(Δuℓ |s) of two-point velocity increments Δuℓ for given pair separation s show up in the nth antisymetric structure functions S-(n)(r)=∫ un(P(u)-P(-u)d u, which scale in agreement with Kolmogorov's prediction, S-(n)(r)∼ r(n/3), for n=2,4,6. The combination of ε with Richardson dispersion ⟨ s2(t)⟩=gε t3, where ⟨ s2(t)⟩ is mean squared pair separation at time t, reveals a Richardson-Obhukov constant of g≃ 0.11± 0.03.