[S-IT16] Planetary cores: Structure, formation, and evolution

[SIT16-07] Impact of thermal core-mantle interaction on back reaction of magnetic field on rotating penetrative convection

*TIRTHARAJ BARMAN¹, SWARANDEEP SAHOO¹ (1.Department of Applied Geophysics, Indian Institute of Technology Indian School of Mines Dhanbad, Jharkhand, India)

Keywords:Stable stratification, Core-mantle interaction, Outer core convection, Geomagnetism

The Earth's and planetary magnetic fields are believed to arise from the convective flow of conducting molten iron in the deep interiors of planetary systems, driven by dynamo action. This dynamo is fueled by the combined effects of thermal and compositional convection at the Earth's core, deriving energy from the secular cooling and solidification of the inner core. The numerical simulation of the geodynamo and the resulting nature of the obtained magnetic fields depend on the imposition of buoyancy profiles that drive convection within the interior. In this study, a magnetoconvection model is employed to examine the impact of electromagnetic forces on fluid flow, particularly in scenarios where the magnetic field is not inherently self-sustained. This sets the study apart from typical dynamo action scenarios. A novel aspect of the study is the incorporation of heterogeneous thermal structure along with thermal stable stratification, ranging from weak to strong strength of stratification. To explore the effects of laterally varying thermal structure at the core-mantle boundary (CMB) and stable stratification near the CMB on super-critical magnetoconvection, a simplified plane layer geometry is studied. As a result, at weakly driven convection regimes, thermal stable stratification confines convective flows to unstable regions, and heterogeneous thermal structures restrict flow at high thermal gradient regions. Conversely, at strongly driven convection regimes, flow penetrates into stable regions in the presence of stable stratification, and flow develops at lower thermal gradient regions along with higher thermal gradient regions in the presence of thermal heterogeneity at the CMB. As a consequence of the combined effect of thermal heterogeneity and stable stratification, in high and low thermal gradient regions flow is dominated by thermal heterogeneity and by stable stratification, respectively. Spectral analysis is also employed to estimate the characteristic length scale of the flow. However, the spectral characteristics undergo changes as the strength of the magnetic field varies, ranging from weak to strong limits. Furthermore, variations in rotation rates alter the flow characteristics and thermal structures.