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.

Abstract Interplanetary (IP) shocks are perturbations observed in the solar wind. IP shocks correlate well with solar activity, being more numerous during times of high sunspot numbers. Earth‐bound IP shocks cause many space weather effects that are promptly observed in geospace and on the ground. Such effects can pose considerable threats to human assets in space and on the ground, including satellites in the upper atmosphere and power infrastructure. Thus, it is of great interest to the space weather community to (a) keep an accurate catalog of shocks observed near Earth, and (b) be able to forecast shock occurrence as a function of the solar cycle (SC). In this work, we use a supervised machine learning regression model to predict the number of shocks expected in SC25 using three previously published sunspot predictions for the same cycle. We predict shock counts to be around 275 ± 10, which is ∼47% higher than the shock occurrence in SC24 (187 ± 8), but still smaller than the shock occurrence in SC23 (343 ± 12). With the perspective of having more IP shocks on the horizon for SC25, we briefly discuss many opportunities in space weather research for the remainder years of SC25. The next decade or so will bring unprecedented opportunities for research and forecasting effects in the solar wind, magnetosphere, ionosphere, and on the ground. As a result, we predict SC25 will offer excellent opportunities for shock occurrences and data availability for conducting space weather research and forecasting.

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.

The Sun provides the energy required to sustain life on Earth and drive our planet’s atmosphere. However, establishing a solid physical connection between solar and tropospheric variability has posed a considerable challenge across the spectrum of Earth-system science. Over the past few years a new picture to describe solar variability has developed, based on observing, understanding and tracing the progression, interaction and intrinsic variability of the magnetized activity bands that belong to the Sun’s 22-year magnetic activity cycle. A solar cycle’s fiducial clock does not run from the canonical min or max, instead resetting when all old cycle polarity magnetic flux is cancelled at the equator, an event dubbed the “termination” of that solar cycle, or terminator. In a recent paper, we demonstrated with high statistical significance, a correlation between the occurrence of termination of the last five solar cycles and the transition from El Niño to La Niña in the Pacific Ocean, and predicted that there would be a transition to La Niña in mid 2020. La Niña did indeed begin in mid-2020, and endured into 2023 as a rare “triple dip” event, but some of the solar predictions made did not occur until late 2021. This work examines what went right, what went wrong, the correlations between El Niño, La Niña and geomagnetic activity indices, and what might be expected for the general trends of large-scale global climate in the next decade.

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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.

We construct a new solar cycle phase clock which maps each of the last 18 solar cycles onto a single normalized epoch for the approximately 22 year Hale (magnetic polarity) cycle, using the Hilbert transform of daily sunspot numbers (SSN) since 1818. The occurrences of solar maxima show almost no Hale cycle dependence, confirming that the clock is synchronized to polarity reversals. The odd cycle minima lead the even cycle minima by 1.1 normalized years, whereas the odd cycle terminators (McIntosh et al. (2019)) lag the even cycle terminators by 2.3 normalized years. The mimimum-terminator interval is thus relatively extended for odd cycles and shortened for even ones. We re-engineer the Sargent(1985,2021) R27 index and combine it with our epoch analysis to obtain a high time resolution parameter for 27 day recurrence in aa, . This reveals that the transition to recurrence, that is, to an ordered solar wind dominated by high speed streams, is fast, occurring within 2-3 solar rotations or less. It resolves an extended late declining phase which is approximately twice as long on even Schwabe cycles as odd. Galactic Cosmic Ray flux rises in step with but then stays high. Our analysis also identifies a slow timescale trend in SSN that simply tracks the Gleissberg cycle. We find that this trend is in phase with the slow timescale trend in the modulus of sunspot latitudes, and in antiphase with that of the R27 index.

This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement No. 1852977. RJL acknowledges support from NASA’s Living With a Star Program. We thank Phil Scherrer and J. Todd Hoeksema for their assistance with, and discussions on, the Wilcox Solar Observatory data, and Dipankar Bannerjee for assistance with the Kodaikanal Observatory data.

We construct a new solar cycle phase clock which maps each of the last 18 solar cycles onto a single normalized epoch for the approximately 22 year Hale (magnetic polarity) cycle, using the Hilbert transform of daily sunspot numbers (SSN) since 1818. We use the clock to study solar and geomagnetic climatology as seen in datasets available over multiple solar cycles. The occurrence of solar maxima on the clock shows almost no Hale cycle dependence, confirming that the clock is synchronized with polarity reversals. The odd cycle minima lead the even cycle minima by ~ 1.1 normalized years, whereas the odd cycle terminators (when sunspot bands from opposite hemispheres have moved to the equator and coincide, thus terminating the cycle, McIntosh(2019)) lag the even cycle terminators by ~ 2.3 normalized years. The average interval between each minimum and terminator is thus relatively extended for odd cycles and shortened for even ones. We re-engineer the R27 index that was orignally proposed by Sargent(1985) to parameterize 27 day recurrences in the aa index. We perform an epoch analysis of autocovariance in the aa index using the Hale cycle clock to obtain a high time resolution parameter for 27 day recurrence, . This reveals that the transition to recurrence, that is, to an ordered solar wind dominated by high speed streams, is fast, occurring within 2-3 solar rotations or less. It resolves an extended late declining phase which is approximately twice as long on even Schwabe cycles as odd ones. We find that Galactic Cosmic Ray flux rises in step with but then stays high. Our analysis also identifies a slow timescale trend in SSN that simply tracks the Gleissberg cycle. We find that this trend is in phase with the slow timescale trend in the modulus of sunspot latitudes, and in antiphase with that of the R27 index.

The Sun provides the energy required to sustain life on Earth and drive our planet's atmospheric circulation. However, establishing a solid physical connection between solar and tropospheric variability has posed a considerable challenge. The canon of solar variability is derived from the 400 years of observations that demonstrates the waxing and waning number of sunspots over an 11(-ish) year period. Recent research has demonstrated the significance of the underlying 22 years magnetic polarity cycle in establishing the shorter sunspot cycle. Integral to the manifestation of the latter is the spatiotemporal overlapping and migration of oppositely polarized magnetic bands. We demonstrate the impact of "terminators"-the end of Hale magnetic cycles-on the Sun's radiative output and particulate shielding of our atmosphere through the rapid global reconfiguration of solar magnetism. Using direct observation and proxies of solar activity going back some six decades we can, with high statistical significance, demonstrate a correlation between the occurrence of terminators and the largest swings of Earth's oceanic indices: the transition from El Nino to La Nina states of the central Pacific. This empirical relationship is a potential source of increased predictive skill for the understanding of El Nino climate variations, a high-stakes societal imperative given that El Nino impacts lives, property, and economic activity around the globe. A forecast of the Sun's global behavior places the next solar cycle termination in mid-2020; should a major oceanic swing follow, then the challenge becomes: when does correlation become causation and how does the process work?

We have published several papers describing solar wind turbulence at 1 au using data from the Advanced Composition Explorer spacecraft. In an oversight that we regret, we never published the list of data intervals that constitute the database of observations. As we have recently returned to this database of observations in comparisons of turbulent observations by the Voyager spacecraft against established results from 1 au, we wish to now correct our oversight and publish the list of intervals that constitute the 1 au observations. Along with this, we show the distribution of some common solar wind parameters as contained within the database.

By obtaining the analytic signal of daily sunspot numbers since 1818 we construct a new solar cycle phase clock that maps each of the last 18 solar cycles onto a single normalized 11 year epoch. This clock orders solar coronal activity and extremes of the aa index, which tracks geomagnetic storms at the Earth's surface over the last 14 solar cycles. We identify geomagnetically quiet intervals that are 40% of the normalized cycle, ±2π/5 in phase or ±2.2 years around solar minimum. Since 1868 only two severe (aa>300 nT) and one extreme (aa>500 nT) geomagnetic storms occurred in quiet intervals; 1–3% of severe (aa>300 nT) geomagnetic storms and 4–6% of C‐, M‐, and X‐class solar flares occurred in quiet intervals. This provides quantitative support to planning resilience against space weather impacts since only a few percent of all severe storms occur in quiet intervals and their start and end times are quantifiable.

We examine both Voyager and Advanced Composition Explorer magnetic field measurements at frequencies that characterize the inertial range using traditional polarization techniques that are designed to characterize plasma waves. Although we find good agreement with both the anticipated spectral index of the power spectrum and the scaling of magnetic power with heliocentric distance, we do not find that the polarization analyses yield results that can be readily described by plasma wave theory. The fluctuations are not circularly polarized and there is a markedly reduced coherence between the components of the fluctuation. The degree of polarization is also generally low, although not as low as the coherence, and the minimum variance direction is essentially random. We conclude that traditional plasma wave theory may not offer a good description for inertial-range fluctuations.

Recent research has demonstrated the existence of a new type of solar event, the "terminator." Unlike the Sun's signature events, flares and Coronal Mass Ejections, the terminator most likely originates in the solar interior, at or near the tachocline. The terminator signals the end of a magnetic activity cycle at the Sun's equator and the start of a sunspot cycle at mid latitudes. Observations indicate that the time difference between these events is very short, less than a solar rotation, in the context of the sunspot cycle. As the (definitive) start and end point of solar activity cycles the precise timing of terminators should permit new investigations into the meteorology of our star's atmosphere. In this letter we use a standard method in signal processing, the Hilbert transform, to identify a mathematically robust signature of terminators in sunspot records and in radiative proxies. Using a linear extrapolation of the Hilbert phase of the sunspot number and F10.7 solar radio flux time series we can achieve higher fidelity historical terminator timing than previous estimates have permitted. Further, this method presents a unique opportunity to project, from analysis of sunspot data, when the next terminator will occur, May 2020 ($+4$, $-1.5$ months), and trigger the growth of sunspot cycle 25.

We examine both Voyager and Advanced Composition Explorer magnetic field measurements at frequencies that characterize the inertial range and evaluate the anisotropy of the fluctuations as they relate to both the compressive component and underlying wavevector anisotropy of the turbulence. The magnetic fluctuation anisotropy as it relates to the compressive component is directly dependent upon both the plasma beta of the thermal proton component and the ratio of magnetic fluctuation magnitude to the strength of the mean magnetic field. This has been seen before at 1 au. The magnetic fluctuation anisotropy in the plane perpendicular to the mean magnetic field, which is a measure of the anisotropy of the underlying wavevector distribution, should depend on the angle between the mean magnetic field and the radial direction and should be confined to values between one and the index of the power spectrum, which is typically 5/3. Our results show that the average of this anisotropy exceeds the value of the spectral index and is out of bounds with the theory. Although the results are suggestive of past analyses, we find that spherical expansion of the turbulence may offer at least a partial explanation of the apparent amplification of this measured anisotropy.