Could hydrodynamic Rossby waves explain the westward drift?

The westward drift of Earth's magnetic field remains an open question in geophysics. Prior research has shown that convection and rotation influence magnetic field behavior. However, no consensus exists on the specific mechanism driving the drift. This gap motivated the exploration of hydrodynamic Rossby waves as a potential explanation. The study builds on established knowledge of fluid dynamics in rotating systems. It introduces a novel hypothesis based on wave propagation in the outer core. The authors propose that certain wave properties could transmit energy westward despite eastward crest movement. This paper contributes a new theoretical framework to a long-standing problem.

The study aims to investigate whether hydrodynamic Rossby waves can explain the westward drift of Earth's magnetic field. The specific problem is understanding how energy might propagate westward despite eastward-moving wave crests. The motivation stems from the need to reconcile observed drift with known fluid dynamics principles. The authors focus on sheet-like flow structures in the outer core. They analyze how these structures might interact with convective upwellings. The study seeks to model energy transmission in rotating fluid systems. The goal is to determine if Rossby waves could account for the drift phenomenon.

The researchers employed the quasi-geostrophic (QG) approximation to model fluid motion. This method assumes horizontal motion independence from rotation axis distance. They accounted for variations in core-mantle boundary slope. The momentum equation was projected onto QG-form flows. A general equation governing evolution was derived. Two initial value problems were adapted for analysis. The first used Cartesian geometry, the second spherical geometry. Both demonstrated westward energy propagation by the waves in question.

The strongest finding is that certain Rossby waves can transmit energy westward. These waves have eastward-moving crests but westward energy propagation. The subset of waves corresponds to sheet-like flow structures. These structures are extended in axial and radial directions. They are likely excited by convective upwellings in the outer core. The QG approximation revealed this energy transmission mechanism. The spherical geometry problem confirmed westward drift preference. The results suggest a plausible explanation for the observed drift.

The authors propose that hydrodynamic Rossby waves may explain the westward drift of Earth's magnetic field. The mechanism relies on sheet-like flow structures in the outer core. These structures are likely excited by convective upwellings. The QG approximation supports the hypothesis. Energy transmission westward is demonstrated in both geometries. The study does not claim this is the only possible explanation. It highlights the need for further analysis of wave properties. The findings suggest a viable mechanism within the constraints of the model.