In the week including Mother’s Day 2024, active region (AR) 13664 became superactive when AR 13668 emerged nearby, causing multiple X-class flares and coronal mass ejections, and an increase in activity level similar to that inferred from geomagnetic storms associated with the historic 1859 events. By analyzing both global warped toroids on which the active regions are strung, and active-region-scale magnetic flux and helicity, we find (i) the north and south toroids have nearly identical warped patterns, with mostly longitudinal wave numbers m = 1–3; (ii) in three longitude intervals the north and south toroids were tipped away from each other in latitude, with a longitude phase shift between them, creating locations most prone to AR eruptions; (iii) on an active region scale, vector magnetic fields deviate far from potential fields, and therefore contain large amounts of magnetic “free energy” available for conversion into kinetic energy and high-temperature radiation; (iv) the positive and negative polarities converge toward each other, facilitating reconnection and magnetic energy release; and (v) rapid changes in magnetic helicity, caused by helicity injection from below that creates helicity imbalances. Despite the coarser resolution of GONG magnetograms, the derived global toroids are strikingly similar to those derived from the Solar Dynamics Observatory's Helioseismic and Magnetic Imager. We conclude that the Mother’s Day superstorms were caused by enhanced magnetic complexity occurring due to intricate interactions among multiple active regions emerging at nearly the same locations. This suggests that predicting the locations of magnetically complex active regions, and studying and tracking their eruptive states using different proxy parameters can greatly improve our ability to forecast intense storms, not only hours but potentially weeks in advance.

The Sun exhibits episodic surges of magnetic activity across a range of temporal and spatial scales, the most prominent of which is the 11-ish year modulation of sunspot production. Beside the 170 (min to max) decadal variation in sunspot production there is a less-explored quasi-annual variation in the range of 25-50 sunspots/year in magnitude. In addition, there is there is a slower, 80 year period, 10-50 variation in the sunspot number, that is commonly referred to as the 'Gleissberg Cycle.' Using a suite of contemporary and historical observations we will illustrate these elements of our star's episodic behavior and present a hypothesis that may provide a consistent physical link between the observed 'climatic', 'decadal' and 'seasonal' magnetic variation of our star.

The “extended solar cycle” indicates that there are two deeply seated toroidal magnetic field bands in each hemisphere. Both bands migrate equatorward as a sunspot cycle progresses. Here, we examine the consequences of global MHD instability of this migrating double-band system in tachocline on the latitudinal structure of unstable modes, which are essentially MHD Rossby waves. We find that latitude-location, latitude-separation, and the amplitude of the bands strongly influence the latitudinal structure and growth rates of the unstable modes of both symmetries about the equator. These properties can lead to “teleconnections” between low- and high-latitudes in each hemisphere and across the equator. High-latitude bands can destabilize low-latitude bands that would otherwise be stable. Stronger high-latitude bands lead to strong interactions between low and high latitude in each hemisphere, but inhibit cross-equatorial band-interaction. Strong cross-equatorial interactions of modes can synchronize cycle minima in north and south. Symmetric and antisymmetric modes of similar amplitudes can lead to substantial asymmetries between north and south. As a solar cycle progresses, excited MHD Rossby waves go through a sequence of changes in latitude structure and growth rate, while maintaining strong links in latitude. These changes and links are theoretical evidence of teleconnections between widely separated latitudes and longitudes in the Sun, which may explain many of the evolving surface magnetic patterns observed as a solar cycle progresses. The wider the separation between high- and low-latitude bands, the earlier the cross-equatorial teleconnection starts in a cycle, and hence the earlier the cycle starts declining.

Polar vortices are ubiquitous features of planetary atmospheric flows, from the Earth-like rocky planets to Jupiter- and Saturn-like gas giant planets. Very little is known about their existence or dynamics on the Sun. What should be expected near the Sun’s pole for the upcoming solar multi-viewpoint and polar missions? Here, we report the magnetohydrodynamic (MHD) nonlinear simulations for the formation and evolution of solar polar vortices using a near-surface MHD shallow-water model. Our findings indicate that the rush to the poles, the migration of magnetic fields toward the pole following the Sun’s magnetic cycle, can positively contribute to the formation of polar vortices. The mechanism proposed here for the formation of polar vortices involves the role of magnetic fields and may be relevant to any star with a magnetic cycle. The Sun’s polar vortices resulting from this mechanism are predominantly MHD, consisting of a tight pair of cyclonic and anticyclonic swirls. This mechanism is likely to operate during all solar cycle phases except the peak, when the polar field reverses. Polar vortices can impact dynamical evolution of global flows and polar fields, which seed the next activity cycle, hence better knowledge of physics of polar regions may lead to improved solar cycle and space weather forecasts.

Physics of magnetohydrodynamic (MHD) Rossby waves in the tachocline-layer were studied by Dikpati et al., using a fluid-particle-trajectory approach along with solving vorticity and induction equations. By extending that model to include a hydrodynamic turbulent convection zone (CZ), we examine how MHD Rossby waves generated in the tachocline might diffuse upward through the CZ to solar surface. We find that pure hydrodynamic Rossby wave amplitudes decline with height due to viscous diffusion at a rate that is independent of viscosity and increases with longitude wavenumber. Fast MHD Rossby waves amplitude declines faster with height for increasing toroidal field, due to their longitude-phase shifting with height, which increases dissipation of kinetic energy in the wave velocities. Slow MHD Rossby waves decline even faster with height because their longitude-phase shifts more rapidly with height, due to their slow phase speed. We conclude that low wavenumber HD and fast MHD Rossby waves, originating in the tachocline, might be detected at the photosphere, but slow MHD Rossby waves should be virtually impossible to detect. We infer from fluid particle trajectories that wave amplitudes declining with height and longitude phase shifting with height associated with decline, implies a powerful mechanism for tangling of magnetic fields, distinct from convective turbulence effects. This could cause a sustained or dissipative local dynamo action triggered by Rossby waves.

Much of the research on the magnetic activity of the Sun has been focused on its axisymmetric component. However, the longitudinal complexity plays a fundamental role in the solar magnetic activity. Rossby waves have recently been proposed as a fundamental mechanism regarding the nonaxisymmetric nature of the solar magnetic fields. Here, we use HMI and MDI magnetic field synoptic maps to evaluate the magnetic field structures’ (mainly active regions) organization and propagation as a function of time and latitude. We demonstrate, using information theory, that the organization of longitudinal structures observed on synoptic maps is proportional to the level of activity at a given latitude. We further show that this organization on the longitudinal structures is persistent and due to long-lived features. The drift velocity of these long-lived photospheric features is inferred and is shown to significantly vary with latitude, and is compatible with the phase speed of tachocline magnetic Rossby waves with a toroidal field in the range of 5–10 kG. Our results suggest that Rossby waves contribute to the organization and propagation of photospheric magnetic features on the timescale of several months and beyond.

Along with a butterfly diagram of sunspots, combined observational studies of ephemeral active regions, X-ray and EUV bright points, plage, filaments, faculae, and prominences demonstrate a pattern, which is known as the Extended Solar Cycle. This pattern indicates that the wings of the sunspot butterfly could be extended to much higher latitudes (up to ∼60°), to an earlier time than the start of a sunspot cycle, hence yielding a strong overlap between cycles. Thus, during the ongoing cycle’s activity near 30° latitude in each hemisphere, the next cycle kicks off at around 60°. By representing these epochs of overlaps by oppositely directed double magnetic bands in each hemisphere, we compute the unstable eigenmodes for MHD Rossby waves at the base of the convection zone and study how the properties of these energetically active Rossby waves change as these band pairs migrate equatorward. We find that in each hemisphere the low-latitude band interacts with the high-latitude band and drives the MHD instability as the solar activity progresses from 35°–15° latitude, which is essentially the rising phase. When the activity proceeds further equatorward from 15°, the interaction between low- and high-latitude bands weakens, and the cross-equatorial interaction between two low-latitude bands in each hemisphere starts. The eigenmodes in the latitude-longitude plane also reflect such changes in their pattern as the bend of the active cycle moves below 15° latitude.

Much of solar activity within a sunspot cycle occurs as bursts, or 'seasons' of strong activity over several months, separated by periods of much less activity.The most important space weather effects occur during these bursty periods.Previous modeling and forecasting efforts have focused on time-scales of hours-to-days and decades-to-centuries.The recent discovery of Rossby waves in the Sun, together with recently developed global models of solar MHD Rossby waves and their interactions with differential rotation and spot-producing magnetic fields, reveal the opportunity to simulate and predict the occurrence, strength and location of enhanced activity bursts a few weeks up to several months in advance.We now have a golden opportunity to fill in this gap in forecasting space weather in these time scales.This requires a) continuous observations of solar Rossby waves by various techniques; b) development of coupled nonlinear MHD models that simulate both global Rossby waves and the much smaller spatial scale emergence of new active regions; c) application of advanced data assimilation techniques to couple surface observations to update the model-system to integrate forward in time for creating forecasts months ahead.Then it will be possible to build operational space weather prediction models to meet the needs of customers and stakeholders, including support of future NASA missions, on a time scale of a few weeks to several months ahead.

We previously identified an event in the solar timeline that appeared to play a role in how sunspot Cycle 23 (SC23) transitioned into sunspot Cycle 24 (SC24). The timeframe for this transition was rapid, taking place over a very short time and perhaps in a time as short as a single solar rotation. Further, we inferred that the transition observed was a critical moment for the Sun’s global-scale magnetic field as it was being manifest in the spatially and temporally overlapping magnetic systems belonging to the Sun’s 22-year (Hale) magnetic cycle. These events have been dubbed as Hale Cycle terminations, or ‘terminators’ for short. Subsequent exploration of the sunspot record revealed a relationship between terminator separation (as a measure of overlap in the Hale Cycles) and the upcoming sunspot cycle amplitude using a Hilbert transform. Finally, we extrapolated the contemporary sunspots data’s Hilbert phase function to project the occurrence of the SC24 terminator in Mid-2020 and inferred that this would result in a large sunspot Cycle 25 (SC25) amplitude. This paper presents observational evidence that the end of SC24 and the initial growth of SC25 followed a terminator that occurred in mid-December 2021 (approximately 12/13/2021). Using this December 2021 terminator identification we can finalize our earlier preliminary forecast of SC25 amplitude - anticipating a peak total monthly sunspot number of 184±17 with 68% confidence, and 184±63 with 95% confidence. Finally, we use other terminator-related superposed epoch analyses developed in parallel work we project the timing of SC25 sunspot maximum to occur between late 2023 to mid 2024.

We investigate whether global toroid patterns and the local magnetic field topology of solar active region (AR) 12673 together can hindcast the occurrence of the biggest X-flares of solar cycle (SC)-24. Magnetic toroid patterns (narrow latitude belts warped in longitude, in which ARs are tightly bound) derived from the surface distributions of ARs, prior and during AR 12673 emergence, reveal that the portions of the south toroid containing AR 12673 was not tipped away from its north-toroid counterpart at that longitude, unlike the 2003 Halloween storms scenario. During the minimum phase there were too few emergences to determine multimode longitudinal toroid patterns. A new emergence within AR 12673 produced a complex nonpotential structure, which led to the rapid buildup of helicity and winding that triggered the biggest X-flare of SC-24, suggesting that this minimum-phase storm can be anticipated several hours before its occurrence. However, global patterns and local dynamics for a peak-phase storm, such as that from AR 11263, behaved like the 2003 Halloween storms, producing the third biggest X-flare of SC-24. AR 11263 was present at the longitude where the north and south toroids tipped away from each other. While global toroid patterns indicate that prestorm features can be forecast with a lead time of a few months, their application to observational data can be complicated by complex interactions with turbulent flows. Complex nonpotential field structure development hours before the storm are necessary for short-term prediction. We infer that minimum-phase storms cannot be forecast accurately more than a few hours ahead, while flare-prone ARs in the peak phase may be anticipated much earlier, possibly months ahead from global toroid patterns.

Through meticulous daily observation of the Sun’s large-scale magnetic field the Wilcox Solar Observatory (WSO) has catalogued two magnetic (Hale) cycles of solar activity. Those two (∼22-year long) Hale cycles have yielded four (∼11-year long) sunspot cycles (numbers 21 through 24). Recent research has highlighted the persistence of the “Extended Solar Cycle” (ESC) and its connection to the fundamental Hale Cycle–albeit through a host of proxies resulting from image analysis of the solar photosphere, chromosphere and corona. This short manuscript presents the correspondence of the ESC, the surface toroidal magnetic field evolution, and the evolution of the Hale Cycle. As Sunspot Cycle 25 begins, interest in observationally mapping the Hale and Extended cycles could not be higher given potential predictive capability that synoptic scale observations can provide.

We present observational signatures of solar cycle 25 onset. Those signatures are visibly following a migratory path from high to low latitudes. They had starting points that are asymmetrically offset in each hemisphere at times that are 21-22 years after the corresponding, same polarity, activity bands of solar cycle 23 started their migration. Those bands define the so-called extended solar cycle. The four magnetic bands currently present in the system are approaching a mutually cancelling configuration, and solar minimum conditions are imminent. Further, using a tuned analysis of the daily band latitude-time diagnostics, we are able to utilize the longitudinal wave number (m=1) variation in the data to more clearly reveal the presence of the solar cycle 25 bands. This clarification illustrates that prevalently active longitudes (different in each hemisphere) exist at mid-latitudes presently, lasting many solar rotations, that can be used for detailed study over the next several years with instruments like the Spectrograph on IRIS, the Spectropolarimeter on Hinode, and, when they come online, similar instruments on the Daniel K. Inouye Solar Telescope (DKIST) as we watch those bands evolve following the cancellation of the solar cycle 24 activity bands at the equator late in 2019.

Features at the Sun’s surface and atmosphere are constantly changing due to its magnetic field. The McIntosh Archive provides a long-term (45 yr) record of these features, digitized from hand-drawn synoptic maps by Patrick McIntosh. Utilizing this data, we create stack plots for coronal holes, i.e., Hovmöller-type plots of latitude bands, for all longitudes, stacked in time, allowing tracking of coronal hole movement. Using a newly developed two-step method of centroid calculation, which includes a Fourier descriptor to represent a coronal hole’s boundary and calculate the centroid by the use of Green’s theorem, we calculate the centroids of 31 unique, long-lived equatorial coronal holes for successive Carrington rotations during the entire solar cycle 23, and estimate their slopes (time versus longitude) as the coronal holes evolve. We compute coronal hole centroid drift speeds from these slopes, and find an eastward (prograde) pattern that is actually retrograde with respect to the local differential rotation. By discussing the plausible physical mechanisms which could cause these long-lived equatorial coronal holes to drift retrograde, we identify either classical or magnetically modified westward-propagating solar Rossby waves, with a speed of a few tens to a few hundreds of meters per second, to be the best candidate for governing the drift of deep-rooted, long-lived equatorial coronal holes. To explore plausible physics of why long-lived equatorial coronal holes appear few in number during solar minimum/early rising phase more statistics are required, which will be studied in future.

EDITORIAL article Front. Astron. Space Sci., 22 June 2022Sec. Extragalactic Astronomy https://doi.org/10.3389/fspas.2022.951370

EDITORIAL article Front. Astron. Space Sci., 10 October 2022Sec. Astrobiology Volume 9 - 2022 | https://doi.org/10.3389/fspas.2022.991696

The Multi-slit Solar Explorer (MUSE) is a proposed NASA MIDEX mission, currently in Phase A, composed of a multi-slit EUV spectrograph (in three narrow spectral bands centered around 171A, 284A, and 108A) and an EUV context imager (in two narrow passbands around 195A and 304A). MUSE will provide unprecedented spectral and imaging diagnostics of the solar corona at high spatial (<0.5 arcsec), and temporal resolution (down to 0.5s) thanks to its innovative multi-slit design. By obtaining spectra in 4 bright EUV lines (Fe IX 171A , Fe XV 284A, Fe XIX-Fe XXI 108A) covering a wide range of transition region and coronal temperatures along 37 slits simultaneously, MUSE will for the first time be able to "freeze" (at a cadence as short as 10 seconds) with a spectroscopic raster the evolution of the dynamic coronal plasma over a wide range of scales: from the spatial scales on which energy is released ( 0.5 arcsec) to the large-scale often active-region size (170 arcsec x 170 arcsec) atmospheric response. We use advanced numerical modeling to showcase how MUSE will constrain the properties of the solar atmosphere on the spatio-temporal scales ( 0.5 arcsec, 20 seconds) and large field-of-view on which various state-of-the-art models of the physical processes that drive coronal heating, solar flares and coronal mass ejections (CMEs) make distinguishing and testable predictions. We describe how the synergy between MUSE, the single-slit, high-resolution Solar-C EUVST spectrograph, and ground-based observatories (DKIST and others) can address how the solar atmosphere is energized, and the critical role MUSE plays because of the multi-scale nature of the physical processes involved. In this first paper, we focus on how comparisons between MUSE observations and theoretical models will significantly further our understanding of coronal heating mechanisms.

Space weather refers to conditions around a star, like our Sun, and its interplanetary space that may affect space- and ground-based assets as well as human life. Space weather can manifest as many different phenomena, often simultaneously, and can create complex and sometimes dangerous conditions. The study of space weather is inherently trans-disciplinary, including subfields of solar, magnetospheric, ionospheric, and atmospheric research communities, but benefiting from collaborations with policymakers, industry, astrophysics, software engineering, and many more. Effective communication is required between scientists, the end-user community, and government organizations to ensure that we are prepared for any adverse space weather effects. With the rapid growth of the field in recent years, the upcoming Solar Cycle 25 maximum, and the evolution of research-ready technologies, we believe that space weather deserves a reexamination in terms of a “risk and resiliency” framework. By utilizing open data science, cross-disciplinary collaborations, information systems, and citizen science, we can forge stronger partnerships between science and industry and improve our readiness as a society to mitigate space weather impacts. The objective of this manuscript is to raise awareness of these concepts as we approach a solar maximum that coincides with an increasingly technology-dependent society, and introduce a unique way of approaching space weather through the lens of a risk and resiliency framework that can be used to further assess areas of improvement in the field.

Rossby waves are found at several levels in the Sun, most recently in its supergranule layer. We show that Rossby waves in the supergranule layer can be excited by an inverse cascade of kinetic energy from the nearly horizontal motions in supergranules. We illustrate how this excitation occurs using a hydrodynamic shallow-water model for a 3D thin rotating spherical shell. We find that initial kinetic energy at small spatial scales inverse cascades quickly to global scales, exciting Rossby waves whose phase velocities are similar to linear Rossby waves on the sphere originally derived by Haurwitz. Modest departures from the Haurwitz formula originate from nonlinear finite amplitude effects and/or the presence of differential rotation. Like supergranules, the initial small-scale motions in our model contain very little vorticity compared to their horizontal divergence, but the resulting Rossby waves are almost all vortical motions. Supergranule kinetic energy could have mainly gone into gravity waves, but we find that most energy inverse cascades to global Rossby waves. Since kinetic energy in supergranules is three or four orders of magnitude larger than that of the observed Rossby waves in the supergranule layer, there is plenty of energy available to drive the inverse-cascade mechanism. Tachocline Rossby waves have previously been shown to play crucial roles in causing seasons of space weather through their nonlinear interactions with global flows and magnetic fields. We briefly discuss how various Rossby waves in the tachocline, convection zone, supergranule layer, and corona can be reconciled in a unified framework.

We study the solar wind helium-to-hydrogen abundance’s ( $A_{ {\mathrm {He}}}$ ) relationship to solar cycle onset. Using OMNI/Lo data, we show that $A_{ {\mathrm {He}}}$ increases prior to sunspot number (SSN) minima. We also identify a rapid depletion and recovery in $A_{ {\mathrm {He}}}$ that occurs directly prior to cycle onset. This $A_{ {\mathrm {He}}}$ shutoff happens at approximately the same time across solar wind speeds ( $v_{\mathrm{sw}}$ ) and the time between successive $A_{ {\mathrm {He}}}$ shutoffs is typically on the order of the corresponding solar cycle length. In contrast to $A_{ {\mathrm {He}}}$ ’s $v_{\mathrm{sw}}$ -dependent phase lag with respect to SSN (Alterman and Kasper, 2019), $A_{ {\mathrm {He}}}$ shutofff’s concurrence across $v_{\mathrm{sw}}$ likely implies it is independent of solar wind acceleration and driven by a mechanism near or below the photosphere. Using brightpoint (BP) measurements to provide context, we infer that $A_{ {\mathrm {He}}}$ shutoff is likely related to the overlap of adjacent solar cycles and the equatorial flux cancelation of the older, extended solar cycle during solar minima.

We explore the fundamental physics of narrow toroidal rings during their nonlinear magnetohydrodynamic evolution at tachocline depths. Using a shallow-water model, we simulate the nonlinear evolution of spot-producing toroidal rings of 6° latitudinal width and a peak field of 15 kG. We find that the rings split; the split time depends on the latitude of each ring. Ring splitting occurs fastest, within a few weeks, at latitudes 20°–25°. Rossby waves work as perturbations to drive the instability of spot-producing toroidal rings; the ring split is caused by the “mixed stress” or cross-correlations of perturbation velocities and magnetic fields, which carry magnetic energy and flux from the ring peak to its shoulders, leading to the ring split. The two split rings migrate away from each other, the high-latitude counterpart slipping poleward faster due to migrating mixed stress and magnetic curvature stress. Broader toroidal bands do not split. Much stronger rings, despite being narrow, do not split due to rigidity from stronger magnetic fields within the ring. Magnetogram analysis indicates the emergence of active regions sometimes at the same longitudes but separated in latitude by 20° or more, which could be evidence of active regions emerging from split rings, which consistently contribute to observed high-latitude excursions of butterfly wings during the ascending, peak, and descending phases of a solar cycle. Observational studies in the future can determine how often new spots are found at higher latitudes than their lower-latitude counterparts and how the combinations influence solar eruptions and space weather events.