Speaker
Description
Venus lacks plate tectonics, yet its highland–lowland topography and clustering of coronae and volcanic provinces suggest large-scale organization of mantle upwelling and downwelling. We test whether such organization can emerge without imposing a preferred lateral asymmetry through nonlinear interaction between near-degenerate convective modes, within a hypothesis termed pulse thermal reorganization (PTR).
We model a two-dimensional, Venus-scaled annulus with depth- and temperature-dependent viscosity, using the exact logarithmic conductive reference state for annular geometry. Linear stability analysis, validated against planar and constant-viscosity benchmarks, reveals a converged crossing between azimuthal wavenumbers m=3 and m=4 at a depth-viscosity contrast of 100 and temperature-viscosity contrast of ~306, with Ra_c ~516. The crossing persists across depth-viscosity contrasts of 20–500 but is sensitive to the conductive reference profile.
When both modes are seeded and viscosity evolves dynamically through a self-consistent Picard–Stokes iteration, nonlinear coupling generates m=1 and m=7 harmonics consistent with the triadic interactions 4−3=1 and 4+3=7. The relative growth rate of the m=4/m=3 amplitude ratio decreases by ~80% between the initial nonlinear evolution and t=5, indicating progressively slowing modal separation. Whether the competition ultimately saturates, reverses, or continues remains unresolved.
These results demonstrate nonlinear spectral coupling and evolving mode competition without imposed lateral asymmetry. We interpret this calculation as a reduced-order mechanistic test of the PTR hypothesis; boundary treatment, spatial and temporal convergence, and extension to fully three-dimensional spherical geometry are required before assessing planetary significance.