Generation of nonlinear internal waves by flow over topography: Rotational effects

Area of Science:

• Fluid dynamics
• Oceanography
• Nonlinear wave phenomena

Background:

• Internal waves are crucial in oceanic mixing and transport.
• Previous studies focused on wave generation without background rotation.
• The forced Ostrovsky equation models wave dynamics in rotating fluids.

Purpose of the Study:

• To investigate internal wave generation by a background current over topography with rotation.
• To analyze the influence of rotation, topography, and current speed on wave characteristics.
• To understand the transition between subcritical, transcritical, and supercritical flow regimes.

Main Methods:

• Utilized the forced Ostrovsky equation for theoretical analysis.
• Employed linearized response analysis to categorize waves.
• Conducted numerical simulations to validate theoretical predictions.

Main Results:

• Identified steady waves downstream and unsteady waves upstream under specific conditions (negative group velocity minimum).
• Demonstrated that increased background current reduces steady wave numbers.
• Highlighted the significant roles of topographic concavity, width, and rotation strength in wave generation.

Conclusions:

• The study provides a comprehensive framework for understanding rotating internal wave generation.
• Nonlinear effects lead to amplitude modulation and coherent wave packet formation.
• Findings are robustly supported by numerical simulations, offering insights into geophysical fluid dynamics.