Nonlinear astrophysical dynamos: a novel data-driven approach for interscale dynamics

ended

Magnetic fields are ubiquitous in the Universe, and are thought to play a key role in evolution of stars, planets, accretion discs and black holes. Although it is generally accepted that these fields are created by the motions of conductive fluids – hydromagnetic dynamos, there is no ab initio predictive theory for their origin and evolution. Because of nonlinear coupling between magnetic field and fluid flow, and also due to extreme parameters of astrophysical objects, dynamos arise from interactions of the flow and field on extremely vast range of space and time scales. This limits the utility of computational approaches. The DynMode project seeks to elucidate the nature of interscale nonlinear interactions using the novel data-based approach from dynamical systems theory, and to create nonlinear reduced-order models of astrophysical dynamos that represent dynamics on large, intermediate and small scales. This is crucial for our understanding of the operation of astrophysical dynamos. During this Fellowship, we will decompose the data of dynamo flows into dynamically relevant blocks (modes), identify principal nonlinear dynamics and energy exchange among those blocks, and create a reduced-order dynamo model by projecting the flow onto them. By analyzing data sets from self-sustained and convective-driven dynamos in different geometries, we will also address the question of intrinsic dynamo features as compared to influence of secondary physical effects and flow geometry. This approach, applied for the first time in dynamo research, will explain interactions between small-scale and large-scale dynamos and their nonlinear saturation, as well as physics of weak and strong geodynamos. The project, bringing together physical modelling of the dynamos, study of the flow and magnetic field structures, and innovative data-driven strategy, has a potential to significantly advance the current understanding of dynamos, and impact wider research community in fluid dynamics