Acoustic-gravity waves in atmospheric and oceanic waveguides

Area of Science:

• Acoustics
• Fluid Dynamics
• Wave Propagation

Background:

• Existing theories describe sound propagation in layered fluids.
• Acoustic-gravity waves (AGWs) are important in various geophysical and astrophysical contexts.
• Understanding AGW behavior in moving media is crucial for accurate modeling.

Purpose of the Study:

• To extend the theory of guided sound propagation to include acoustic-gravity waves (AGWs) in waveguides with piecewise continuous parameters.
• To analyze the orthogonality of AGW normal modes in both moving and motionless media.
• To develop a perturbation theory for quantifying the significance of gravity and compressibility, and the sensitivity of normal modes to environmental variations.

Main Methods:

• Extension of guided sound propagation theory.
• Establishment of AGW normal mode orthogonality.
• Development of perturbation theory to analyze mode sensitivity.
• Analysis of phase and group speeds for waveguides with arbitrary stratification.

Main Results:

• Orthogonality of AGW normal modes confirmed in moving and motionless media.
• Perturbation theory quantifies the influence of gravity, compressibility, and environmental parameters on normal modes.
• Universal properties of phase and group speeds identified for arbitrarily stratified waveguides.
• The Lamb wave is identified as the sole AGW normal mode capable of non-dispersive propagation in layered media.

Conclusions:

• The extended theory provides a robust framework for analyzing AGWs in complex fluid environments.
• Sensitivity analysis highlights key parameters influencing AGW propagation.
• The universal properties of speeds and the unique nature of the Lamb wave offer valuable insights for wave phenomena in stratified media.