Long-term forcing of Sun's coronal field, open flux and cosmic ray modulation potential during grand minima, maxima and regular activity phases by the solar dynamo mechanism

Magnetic fields generated in the Sun's interior by the solar dynamo mechanism drive solar activity over a range of time-scales. While space-based observations of the Sun's corona exist only for few decades, direct sunspot observations exist for a few centuries, solar open flux and cosmic ray flux variations can be reconstructed through studies of cosmogenic isotopes over thousands of years. While such reconstructions indicate the presence of extreme solar activity fluctuations in the past, causal links between millennia scale dynamo activity, consequent coronal field, solar open flux and cosmic ray modulation remain elusive. By utilizing a stochastically forced solar dynamo model we perform long-term simulations to illuminate how the dynamo generated magnetic fields govern the structure of the solar corona and the state of the heliosphere -- as indicated by variations in the open flux and cosmic ray modulation potential. We establish differences in the nature of the large-scale structuring of the solar corona during grand maximum, minimum, and regular solar activity phases and simulate how the open flux and cosmic ray modulation potential varies over time scales encompassing these different phases of solar activity. We demonstrate that the power spectrum of simulated and reconstructed solar open flux are consistent with each other. Our study provides the theoretical basis for interpreting long-term solar cycle variability based on reconstructions relying on cosmogenic isotopes and connects solar internal variations to the forcing of the state of the heliosphere.Comment: 15 Pages, 8 Figures, Submitted to MNRA

Skyrmions and magnetic bubbles in spin-orbit coupled metallic magnets

Motivated by the observation of Skyrmion-like magnetic textures in 2D itinerant ferromagnets Fe$_n$GeTe$_2$ ($n \geq3$), we develop a microscopic model combining itinerant magnetism and spin-orbit coupling on a triangular lattice. The ground state of the model in the absence of magnetic field consists of filamentary magnetic domain walls revealing a striking similarity with our magnetic force microscopy experiments on Fe$_3$GeTe$_2$. In the presence of magnetic field, these filaments were found to break into large size magnetic bubbles in our experiments. We identify uniaxial magnetic anisotropy as an important parameter in the model that interpolates between magnetic Skyrmions and ferromagnetic bubbles. Consequently, our work uncovers new topological magnetic textures that merge properties of Skyrmions and ferromagnetic bubbles

Long-term forcing of the Sun’s coronal field, open flux, and cosmic ray modulation potential during grand minima, maxima, and regular activity phases by the solar dynamo mechanism

Abstract Magnetic fields generated in the Sun’s interior by the dynamo mechanism drive solar activity over a range of time-scales. Direct sunspot observations exist for a few centuries; reconstructed variations based on cosmogenic isotopes in the solar open flux and cosmic ray flux exist over thousands of years. While such reconstructions indicate the presence of extreme solar activity fluctuations in the past, causal links between millennia scale dynamo activity, consequent coronal field, solar wind, open flux and cosmic ray flux variations remain elusive; a lack of coronal field observations compounds this issue. By utilizing a stochastically forced solar dynamo model and potential field source surface extrapolation, we perform long-term simulations to illuminate how dynamo generated magnetic fields govern the structure of the solar corona and the state of the heliosphere — as indicated by variations in the open flux and cosmic ray modulation potential. We establish differences in the nature of the large-scale structuring of the solar corona during grand maximum, minimum, and regular solar activity phases and simulate how the open flux and cosmic ray modulation potential vary across these different phases of activity. We demonstrate that the power spectrum of simulated and observationally reconstructed solar open flux time series are consistent with each other. Our study provides the theoretical foundation for interpreting long-term solar cycle variations inferred from cosmogenic isotope based reconstructions and establishes causality between solar internal variations to the forcing of the state of the heliosphere

The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations

On 2017 August 21, a total solar eclipse swept across the contiguous United States, providing excellent opportunities for diagnostics of the Sun's corona. The Sun's coronal structure is notoriously difficult to observe except during solar eclipses; thus, theoretical models must be relied upon for inferring the underlying magnetic structure of the Sun's outer atmosphere. These models are necessary for understanding the role of magnetic fields in the heating of the corona to a million degrees and the generation of severe space weather. Here we present a methodology for predicting the structure of the coronal field based on model forward runs of a solar surface flux transport model, whose predicted surface field is utilized to extrapolate future coronal magnetic field structures. This prescription was applied to the 2017 August 21 solar eclipse. A post-eclipse analysis shows good agreement between model simulated and observed coronal structures and their locations on the limb. We demonstrate that slow changes in the Sun's surface magnetic field distribution driven by long-term flux emergence and its evolution governs large-scale coronal structures with a (plausibly cycle-phase dependent) dynamical memory timescale on the order of a few solar rotations, opening up the possibility for large-scale, global corona predictions at least a month in advance