The Sun’s activity cycle governs the radiation, particle and magnetic flux in the heliosphere creating hazardous space weather. Decadal-scale variations define space climate and force the Earth’s atmosphere. However, predicting the solar cycle is challenging. Current understanding indicates a short window for prediction best achieved at previous cycle minima. Utilizing magnetic field evolution models for the Sun’s surface and interior we perform the first century-scale, data-driven simulations of solar activity and present a scheme for extending the prediction window to a decade. Our ensemble forecast indicates cycle 25 would be similar or slightly stronger than the current cycle and peak around 2024. Sunspot cycle 25 may thus reverse the substantial weakening trend in solar activity which has led to speculation of an imminent Maunder-like grand minimum and cooling global climate. Our simulations demonstrate fluctuation in the tilt angle distribution of sunspots is the dominant mechanism responsible for solar cycle variability.

Filaments and coronal holes, two principal features observed in the solar corona are sources of space weather variations. Filament formation is closely associated with polarity inversion lines (PIL) on the solar photosphere which separate positive and negative polarities of the surface magnetic field. The origin of coronal holes is governed by largescale unipolar magnetic patches on the photosphere from where open magnetic field lines extend to the heliosphere. We study properties of filaments, PILs and coronal holes in solar cycles 20, 21, 22 and 23 utilizing the McIntosh archive. We detect a prominent cyclic behavior of filament length, PIL length, and coronal hole area with significant correspondence with the solar magnetic cycle. The spatio-temporal evolution of the geometric centers of filaments shows a butterfly-like structure and distinguishable pole-ward migration of long filaments during cycle maxima. We identify this rush to the poles of filaments to be co-temporal with the initiation of polar field reversal as gleaned from Mount Wilson and Wilcox Solar Observatory polar field observations and quantitatively establish their temporal correspondence. We analyze the filament tilt angle distribution to constrain their possible origins. Majority of the filaments exhibit negative and positive tilt angles in the northern and the southern hemispheres, respectively -strongly suggesting that their formation is governed by the overall large-scale magnetic field distribution on the solar photosphere and not by the small-scale intra-active region magnetic field configurations. We also investigate the hemispheric asymmetry in filaments, PILs, and coronal holes. We find that the hemispheric asymmetry in filaments and PILs are positively correlated -whereas coronal hole asymmetry is uncorrelated -with sunspot area asymmetry.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractOn 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.

During solar minimum, the Sun is relatively inactive with few sunspots observed on the solar surface. Consequently, we observe a smaller number of highly energetic events such as solar flares or coronal mass ejections (CMEs), which are often associated with active regions on the photosphere. Nonetheless, our magnetofrictional simulations during the minimum period suggest that the solar corona is still dynamically evolving in response to the large-scale shearing velocities on the solar surface. The non-potential evolution of the corona leads to the accumulation of magnetic free energy and helicity, which is periodically shed in eruptive events. We find that these events fall into two distinct classes: One set of events are caused by eruption and ejection of low-lying coronal flux ropes, and they could explain the origin of occasional CMEs during solar minimum. The other set of events are not driven by destabilisation of low-lying structures but rather by eruption of overlying sheared arcades. These could be associated with streamer blowouts or stealth CMEs. The two classes differ significantly in the amount of magnetic flux and helicity shed through the outer coronal boundary. We additionally explore how other measurables such as current, open magnetic flux, free energy, coronal holes, and the horizontal component of the magnetic field on the outer model boundary vary during the two classes of event. This study emphasises the importance and necessity of understanding the dynamics of the coronal magnetic field during solar minimum.

Aims. Hemispheric irregularities of solar magnetic activity is a well-observed phenomenon, the origin of which has been studied through numerical simulations and data analysis techniques. In this work we explore possible causes generating north-south asymmetry in the reversal timing and amplitude of the polar field during cycle minimum. Additionally, we investigate how hemispheric asymmetry is translated from cycle to cycle. Methods. We pursued a three-step approach. Firstly, we explored the asymmetry present in the observed polar flux and sunspot area by analysing observational data of the last 110 years. Secondly, we investigated the contribution from various factors involved in the Babcock–Leighton mechanism to the evolution and generation of polar flux by performing numerical simulations with a surface flux transport model and synthetic sunspot input profiles. Thirdly, translation of hemispheric asymmetry in the following cycle was estimated by assimilating simulation-generated surface magnetic field maps at cycle minimum in a dynamo simulation. Finally, we assessed our understanding of hemispheric asymmetry in the context of observations by performing additional observational data-driven simulations. Results. Analysis of observational data shows a profound connection between the hemispheric asymmetry in the polar flux at cycle minimum and the total hemispheric activity during the following cycle. We find that the randomness associated with the tilt angle of sunspots is the most crucial element among diverse components of the Babcock–Leighton mechanism in resulting hemispheric irregularities in the evolution of polar field. Our analyses with dynamo simulations indicate that an asymmetric poloidal field at the solar minimum can introduce significant north-south asymmetry in the amplitude and timing of peak activity during the following cycle. While observational data-driven simulations reproduce salient features of the observed asymmetry in the solar cycles during the last 100 years, we speculate that fluctuations in the mean-field α-effect and meridional circulation can have finite contributions in this regard.