Double-diffusive convection driven dynamos in the strong-field regime

The Earth's liquid outer core is mainly composed of iron and nickel. The secular cooling of the inner core releases latent heat and light elements, driving convection in the liquid outer core and promoting the upward transport of these lighter elements, thereby forming thermal and compositional driven convection. However, due to the uncertainty of the temperature distribution within the liquid outer core, two types of convection may occur: top-heavy and salt-fingers double-diffusive convection, the latter characterized by a thermal stable stratification where the thermal gradient is stabilizing. Most dynamo models, however, do not account for such complex driving mechanisms. Instead, they simplify the system by assuming no distinction between thermal and compositional convection, which is termed the co-density model. In our study, we compared the top-heavy double-diffusive model with the co-density model within the strong field regime, where the Lorentz force plays a significant role. Our results suggest that, under strong fields and similar magnetic Reynolds numbers, different types of buoyancy do not show significant differences in driving the dynamo process. Furthermore, we investigate the effects of varying the strength of thermal stratification on the dynamo. Our analysis indicates that when the thermal stratification becomes sufficiently strong, it can suppress convection entirely, ultimately halting the dynamo process.