EGU22-7004
https://doi.org/10.5194/egusphere-egu22-7004
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Turbulent Energy Cascade in the Gulf of Mexico

Yinxiang Ma1, Jianyu Hu1,2, and Yongxiang Huang1,2,3
Yinxiang Ma et al.
  • 1State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
  • 2Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China
  • 3SJTU SMSE-Mingguang Joint Research Center for Advanced Palygorskite Materials, Mingguang 239400, China

Due  to the extreme complexity of the oceanic dynamics, e.g., stratification, air-sea interaction,  waves, current, tide, etc., the corresponding turbulent cascade remains unknown. The third-order longitudinal structure-function is often employed to diagnose  the cascade direction and intensity, which is written as  SLLL(r)=< Δ uL3(r)>, where Δ uL is the  velocity increment along the distance vector r, and r is the modulus of r. In the case of  three-dimension homogeneous and isotropic turbulence, SLLL(r) is scaled as -4/5εr in the inertial range, where ε is the energy dissipation rate per unit.  In this work, SLLL(r) is estimated for two experimental velocities that obtained in the Gulf of Mexico, namely Grand LAgrangian Deployment (GLAD) and the LAgrangian Submesoscale ExpeRiment (LASER). The experimental SLLL(r) for both experiments shows a transition from negative values to a positive one roughly at rT=10km, corresponding to a timescale  around τT=12-hour (e.g., τT=rT/urms with urms ≈0.24m/s.  Power-law is evident for the scale on the range 0.01≤ r≤1km as SLLL(r)∼ -r1.45±0.10, and for the scale on the range 30≤ r≤300km as SLLL(r)∼ r1.45±0.10. Note that a weak stratification with depth of 10∼15m has been reported for the GLAD experiment, indicating a quasi-2D flow topography. The scaling ranges are above this stratification depth. Hence, the famous Kraichnan's 2D turbulence theory or the geostrophic turbulence proposed by Charney are expected to be applicable. However, due to the complexity of real oceanic flows, hypotheses behind these theories cannot be verified either directly or indirectly. To simplify the situation, we still consider here the sign of  SLLL(r) as an indicator of the energy cascade. It thus suggests a possible forward energy cascade below the spatial scale rT, and an inverse one above the scale  spatial rT.  While, the scaling exponents 1.45 are deserved more studied in the future if more data is available.

 

Ref.

Charney, J. G. (1971). Geostrophic turbulence. J. Atmos. Sci., 28(6), 1087-1095.

Frisch, U., & Kolmogorov, A. N. (1995). Turbulence: the legacy of AN Kolmogorov. Cambridge University Press.

Alexakis, A., & Biferale, L. (2018). Cascades and transitions in turbulent flows. Phys. Rep., 767, 1-101.

Dong, S., Huang, Y., Yuan, X., & Lozano-Durán, A. (2020). The coherent structure of the kinetic energy transfer in shear turbulence. J. Fluid Mech., 892, A22.

Poje, A. C., Özgökmen, T. M., Bogucki, D. J., & Kirwan, A. D. (2017). Evidence of a forward energy cascade and Kolmogorov self-similarity in submesoscale ocean surface drifter observations. Phys. Fluids, 29(2), 020701.

How to cite: Ma, Y., Hu, J., and Huang, Y.: Turbulent Energy Cascade in the Gulf of Mexico, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7004, https://doi.org/10.5194/egusphere-egu22-7004, 2022.

Comments on the display material

to access the discussion