Geophysical & Astrophysical Fluid Dynamics Seminar Series

Title：Bidirectional energy transfer across scales in geophysical

Speaker：Prof. Xie, Jinhan (Peking University)

Location: Middle conference room, 3rd floor

Time：10:00 am Sep 23, 2025 (Tus)

Abstract:
In 1941, Kolmogorov proposed the 4/5 law for the inertial range in three-dimensional isotropic turbulence, which links measurable third-order structure functions with energy transfer. The inertial-range theories are applied to quantify the direction and magnitude of energy transfer in natural turbulence. However, the applicability of these theories is limited due to the effects of forcing scale and bidirectional energy transfer. Thus, expressions for structure functions beyond the inertial range are required. We derive a forcing-scale-resolving global expression that captures the bidirectional energy transfer. We apply this expression to analyse the drifter data in the Gulf of Mexico and provide evidence for bidirectional energy transfer in ocean turbulence. By analyzing the third-order structure functions of measured data for solar winds, we show how simultaneous upscale and downscale energy transfers occur in solar wind, leading statistically to equipartition of the turbulent energy flux. Our study sheds light on the paradigm of the existence of dual energy cascades in astrophysical plasmas, identifying the scales at which energy sources act in the magnetohydrodynamic regime, driving turbulent dynamics in the solar wind. These findings in the ocean and solar imply the universal feature of bidirectional energy transfer in geophysical turbulence.

Bio:
Jin-Han Xie is an Associate Professor at Peking University. He was a Courant instructor at Courant institute advised by Prof. Oliver Bühler, before that he was a postdoctoral researcher at UC Berkeley advised by Prof. Edgar Knobloch.
He got his PhD at the University of Edinburgh under the supervision of Prof. Jacuqes Vanneste and he received Batchelor degree at Peking University. His research focuses on geophysical fluid dynamics, turbulence and internal waves.