Penetrative rotating magnetoconvection subject to lateral variations in temperature gradients

Abstract

Convection-driven flows in planetary interiors exhibit rich dynamics owing to multiple spatio-temporally varying forcing conditions and physical constraints. In particular, the churning of liquid metals in the Earth's outer core, responsible for the dynamic geomagnetic field, is subjected to lower mantle thermal heterogeneity. Besides, the plausible existence of a stable stratification layer below the mantle influences the columnar convection. These additional symmetry-breaking constraints, motivated from geophysical scenario of the Earth's thermal core--mantle interaction, modulate the otherwise periodic and axially invariant convection flow patterns. Thus, the present study focuses on qualitative characterization and parametric quantification of rotating penetrative convection in the presence of magnetic induction effects with an aim to understand the role of the lower mantle on core convection thermally. Using complementing computational and theoretical calculations, the present study estimates the depth of penetration in bounded and unbounded fluid domains. Apart from qualitative differences in convective flow patterns from the reference homogeneous configurations, the additional constraints spatially modulate the extent of penetration into stable regions. Confinement effects, adding to the damping of penetrative convection, arising out of boundary constraints are quantified for bounded geometry. Appropriate normalizations, implemented to eliminate such effects, result in amended penetration depth estimates that align with the qualitative characteristics obtained for unbounded domains. Exact closed-form expressions for the depth of penetration are obtained, providing insights into the role of individual contributions of multiple physical constraints. Implications are speculated for realistic, yet unreachable, regimes of geophysical conditions of planetary cores.