Search

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., Comment: 18 pages, 8 figures

We investigate whether global toroid patterns and the local magnetic field topology of solar active region AR12673 together can hindcast occurrence of the biggest X-flare of solar cycle (SC)-24. Magnetic toroid patterns (narrow latitude-belts warped in longitude, in which active regions are tightly bound) derived from surface distributions of active regions, prior/during AR12673 emergence, reveal that the portions of the South-toroid containing AR12673 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 multi-mode longitudinal toroid patterns. A new emergence within AR12673 produced a complex/non-potential structure, which led to rapid build-up of helicity/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 AR11263, behaved like 2003 Halloween storms, producing the third biggest X-flare of SC-24. AR11263 was present at the longitude where the North/South toroids tipped-away from each other. While global toroid patterns indicate that pre-storm features can be forecast with a lead-time of a few months, its application on observational data can be complicated by complex interactions with turbulent flows. Complex/non-potential 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 active regions in peak-phase may be anticipated much earlier, possibly months ahead from global toroid patterns.

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$\pm$17 with 68\% confidence, and 184$\pm$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., Comment: 16 pages, 10 figures - Accepted to appear in Frontiers

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 ($\sim$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., Comment: 10 pages, 5 figures, submitted to Frontiers in Solar and Stellar Physics

The total solar eclipse of August 21, 2017, crossed the whole width of North America, the first occasion for this during the modern age of consumer electronics. Accordingly, it became a great opportunity to engage the public and to enlist volunteer observers with relatively high-level equipment; our program ("Eclipse Megamovie") took advantage of this as a means of creating a first-ever public database of such eclipse photography. This resulted in a large outreach program, involving many hundreds of individuals, supported almost entirely on a volunteer basis and with the institutional help of Google, the Astronomical Society of the Pacific, and the University of California, Berkeley. The project home page is \url{http://eclipsemegamovie.org}, which contains the movie itself. We hope that our comments here will help with planning for similar activities in the total eclipse of April 8, 2024.

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., Comment: 46 pages, 22 figures, submitted to ApJ

The Sun's variability is controlled by the progression and interaction of the magnetized systems that form the 22-year magnetic activity cycle (the "Hale Cycle'') as they march from their origin at $\sim$55 degrees latitude to the equator, over $\sim$19 years. We will discuss the end point of that progression, dubbed "terminator'' events, and our means of diagnosing them. Based on the terminations of Hale Magnetic Cycles, we construct a new solar activity 'clock' which maps all solar magnetic activity onto a single normalized epoch. The Terminators appear at phase $0 * 2\pi$ on this clock (by definition), then solar polar field reversals commence at $\sim0.2 * 2\pi$, and the geomagnetically quiet intervals centered around solar minimum, start at $\sim0.6 * 2\pi$ and end at the terminator, lasting 40% of the normalized cycle length. With this onset of quiescence, dubbed a "pre-terminator,'' the Sun shows a radical reduction in active region complexity and (like the terminator events) is associated with the time when the solar radio flux crosses F10.7=90 sfu -- effectively marking the commencement of solar minimum conditions. In this paper we use the terminator-based clock to illustrate a range of phenomena that further emphasize the strong interaction of the global-scale magnetic systems of the Hale Cycle. arXiv:2010.06048 is a companion article., Comment: 28 pages, 8 figures, 1 table, submitted to Solar Physics (revised and resubmitted)

We investigate the occurrence of the "extended solar cycle" (ESC) as it occurs in a host observational data spanning 140 years. Investigating coronal, chromospheric, photospheric and interior diagnostics we develop a consistent picture of solar activity migration linked to the 22-year Hale (magnetic) cycle using superposed epoch analysis (SEA) using previously identified Hale cycle termination events as the key time for the SEA. Our analysis shows that the ESC and Hale cycle, as highlighted by the terminator-keyed SEA, is strongly recurrent throughout the entire observational record studied, some 140 years. Applying the same SEA method to the sunspot record confirms that Maunder's butterfly pattern is a subset of the underlying Hale cycle, strongly suggesting that the production of sunspots is not the fundamental feature of the Hale cycle, but the ESC is. The ESC (and Hale cycle) pattern highlights the importance of 55\degree\ latitude in the evolution, and possible production, of solar magnetism., Comment: 29 pages, 15 figures. Movies of Fig.14 panels available on request to mscott@ucar.edu. Submitted to Solar Physics

The Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities which will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the Daniel K. Inouye Solar Telescope hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute.

Understanding many physical processes in the solar atmosphere requires determination of the magnetic field in each atmospheric layer. However, direct measurements of the magnetic field in the Sun's corona are difficult to obtain. Using observations with the Coronal Multi-channel Polarimeter, we have determined the spatial distribution of the plasma density in the corona, and the phase speed of the prevailing transverse magnetohydrodynamic waves within the plasma. We combine these measurements to map the plane-of-sky component of the global coronal magnetic field. The derived field strengths in the corona from 1.05 to 1.35 solar radii are mostly 1-4 Gauss. These results demonstrate the capability of imaging spectroscopy in coronal magnetic field diagnostics., Comment: Published in Science, File includes the main text and supplementary materials. This is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science , (2020-08-07), doi: 10.1126/science.abb4462 (https://science.sciencemag.org/content/369/6504/694)

The Parker Solar Probe (PSP) and Solar Orbiter missions are designed to make groundbreaking observations of the Sun and interplanetary space within this decade. We show that a particularly interesting in situ observation of an interplanetary coronal mass ejection (ICME) by PSP may arise during close solar flybys ($< 0.1$~AU). During these times, the same magnetic flux rope inside an ICME could be observed in situ by PSP twice, by impacting its frontal part as well as its leg. Investigating the odds of this situation, we forecast the ICME rate in solar cycle 25 based on 2 models for the sunspot number (SSN): (1) the forecast of an expert panel in 2019 (maximum SSN = 115), and (2) a prediction by McIntosh et al. (2020, maximum SSN = 232). We link the SSN to the observed ICME rates in solar cycles 23 and 24 with the Richardson and Cane list and our own ICME catalog, and calculate that between 1 and 7 ICMEs will be observed by PSP at heliocentric distances $< 0.1$ AU until 2025, including 1$\sigma$ uncertainties. We then model the potential flux rope signatures of such a double-crossing event with the semi-empirical 3DCORE flux rope model, showing a telltale elevation of the radial magnetic field component $B_R$, and a sign reversal in the component $B_N$ normal to the solar equator compared to field rotation in the first encounter. This holds considerable promise to determine the structure of CMEs close to their origin in the solar corona., Comment: 11 pages, 6 figures, accepted for publication in the Astrophysical Journal on 2020 September 17

The Sun exhibits a well-observed modulation in the number of spots on its disk over a period of about 11 years. From the dawn of modern observational astronomy sunspots have presented a challenge to understanding -- their quasi-periodic variation in number, first noted 175 years ago, stimulates community-wide interest to this day. A large number of techniques are able to explain the temporal landmarks, (geometric) shape, and amplitude of sunspot "cycles," however forecasting these features accurately in advance remains elusive. Recent observationally-motivated studies have illustrated a relationship between the Sun's 22-year (Hale) magnetic cycle and the production of the sunspot cycle landmarks and patterns, but not the amplitude of the sunspot cycle. Using (discrete) Hilbert transforms on more than 270 years of (monthly) sunspot numbers we robustly identify the so-called "termination" events that mark the end of the previous 11-yr sunspot cycle, the enhancement/acceleration of the present cycle, and the end of 22-yr magnetic activity cycles. Using these we extract a relationship between the temporal spacing of terminators and the magnitude of sunspot cycles. Given this relationship and our prediction of a terminator event in 2020, we deduce that Sunspot Cycle 25 could have a magnitude that rivals the top few since records began. This outcome would be in stark contrast to the community consensus estimate of sunspot cycle 25 magnitude., Comment: 12 pages, 6 figures. Submitted to Nature Astronomy 3/9/2020. In third iteration with reviewers. Revised and reformatted for Solar Physics - 15 pages, 8 figures. 8/25/2020

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 ($v_\mathrm{sw}$), implying that it is formed by a mechanism distinct from the one that drives $A_\mathrm{He}$'s solar cycle scale variation and $v_\mathrm{sw}$-dependent phase offset with respect to SSN. The time between successive $A_\mathrm{He}$ shutoffs is typically on the order of the corresponding solar cycle length. Using Brightpoint (BP) measurements to provide context, we infer that this 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., Comment: Accepted in Solar Physics

Plasma outflows from the edges of active regions have been suggested as a possible source of the slow solar wind. Spectroscopic measurements show that these outflows have an enhanced elemental composition, which is a distinct signature of the slow wind. Current spectroscopic observations, however, do not have sufficient spatial resolution to distinguish what structures are being measured or to determine the driver of the outflows. The High-resolution Coronal Imager (Hi-C) flew on a sounding rocket in May, 2018, and observed areas of active region outflow at the highest spatial resolution ever achieved (250 km). Here we use the Hi-C data to disentangle the outflow composition signatures observed with the Hinode satellite during the flight. We show that there are two components to the outflow emission: a substantial contribution from expanded plasma that appears to have been expelled from closed loops in the active region core, and a second contribution from dynamic activity in active region plage, with a composition signature that reflects solar photospheric abundances. The two competing drivers of the outflows may explain the variable composition of the slow solar wind., Comment: To be published in The Astrophysical Journal. Figures 1, 2, 3 and 12 are reduced resolution to meet size requirements. The original figures will appear in the published version

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., Comment: 18 pages, 6 figures, 1 table. Final (minor corrections) revision as submitted to Solar Physics, January 2020

In the recent years there has been a resurgence of the study of Extended Solar Cycles (ESCs) through observational proxies mainly in Extreme Ultraviolet. But most of them are limited only to space-based era covering only about two solar cycles. Long-term historical data-sets are worth in examining the consistency of ESCs. Kodaikanal Solar Observatory (KSO) and Mount Wilson Observatory (MWO) are the two major sources of long-term Ca II K digitised spectroheliograms covering the temporal spans 1907-2007 and 1915-1985 respectively. In this study, we detected supergranule boundaries, commonly known as networks, using the Carrington maps from both KSO and MWO datasets. Subsequently we excluded the plage areas to consider only quiet sun (QS) and detected small scale bright features through intensity thresholding over the QS network. Latitudinal density of those features, which we named as `Network Bright Elements' (NBEs), could clearly depict the existence of overlapping cycles with equator-ward branches starting at latitude $\approx 55^{\circ}$ and taking about $15\pm1$ years to reach the equator. We performed superposed epoch analysis to depict the similarity of those extended cycles. Knowledge of such equator-ward band interaction, for several cycles, may provide critical constraints on solar dynamo models., Comment: 16 pages, 4 figures, 1 table, accepted for publication in ApJL

We observe the abrupt end of solar activity cycles at the Sun's equator by combining almost 140 years of observations from ground and space. These "terminator" events appear to be very closely related to the onset of magnetic activity belonging to the next sunspot cycle at mid-latitudes and the polar-reversal process at high-latitudes. Using multi-scale tracers of solar activity we examine the timing of these events in relation to the excitation of new activity and find that the time taken for the solar plasma to communicate this transition is of the order of one solar rotation, but could be shorter. Utilizing uniquely comprehensive solar observations from the Solar Terrestrial Relations Observatory (STEREO), and Solar Dynamics Observatory (SDO) we see that this transitional event is strongly longitudinal in nature. Combined, these characteristics imply that magnetic information is communicated through the solar interior rapidly. A range of possibilities exist to explain such behavior: the presence of magnetic reconnection in the deep interior, internal gravity waves on the solar tachocline, or that the magnetic fields present in the Sun's convection zone could be very large, with a poloidal field strengths reaching 50k - considerably larger than conventional explorations of solar and stellar dynamos estimate. Regardless of mechanism responsible, the rapid timescales demonstrated by the Sun's global magnetic field reconfiguration present strong constraints on first-principles numerical simulations of the solar interior and, by extension, other stars., Comment: Submitted [10/2017] to, and rejected [01/2019] by, Nature Astronomy. Accepted Solar Physics [6/1/2019]

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 across the spectrum of Earth-system science. The canon of solar variability, the solar fiducial clock, lies almost exclusively with the 400 years of human telescopic observations that demonstrates the waxing and waning number of sunspots, over an 11(ish) year period. Recent research has demonstrated the critical importance of the underlying 22-year magnetic polarity cycle in establishing the shorter sunspot cycle. Integral to the manifestation of the latter is the spatio-temporal overlapping and migration of oppositely polarized magnetic bands. The points when these bands emerge at high solar latitudes and cancel at the equator are separated by almost 20 years. Here we demonstrate the impact of these "termination" points on the Sun's radiative output and particulate shielding of our atmosphere through the dramatically rapid reconfiguration of solar magnetism. These events reset the Sun's fiducial clock and present a new portal to explore the Sun-Earth connection. Using direct observation and proxies of solar activity going back six decades we can, with high statistical significance, demonstrate an apparent correlation between the solar cycle terminations and the largest swings of Earth's oceanic indices---a previously overlooked correspondence. Forecasting the Sun's global behavior places the next solar termination in early 2020; should a major oceanic swing follow, our challenge becomes: when does correlation become causation and how does the process work?, Comment: 34 pages, 12 figures, 3 tables

The authors of this report met on 28-30 March 2018 at the New Jersey Institute of Technology, Newark, New Jersey, for a 3-day workshop that brought together a group of data providers, expert modelers, and computer and data scientists, in the solar discipline. Their objective was to identify challenges in the path towards building an effective framework to achieve transformative advances in the understanding and forecasting of the Sun-Earth system from the upper convection zone of the Sun to the Earth's magnetosphere. The workshop aimed to develop a research roadmap that targets the scientific challenge of coupling observations and modeling with emerging data-science research to extract knowledge from the large volumes of data (observed and simulated) while stimulating computer science with new research applications. The desire among the attendees was to promote future trans-disciplinary collaborations and identify areas of convergence across disciplines. The workshop combined a set of plenary sessions featuring invited introductory talks and workshop progress reports, interleaved with a set of breakout sessions focused on specific topics of interest. Each breakout group generated short documents, listing the challenges identified during their discussions in addition to possible ways of attacking them collectively. These documents were combined into this report-wherein a list of prioritized activities have been collated, shared and endorsed., Comment: Workshop Report

We explore new opportunities for solar physics that could be realized by future missions providing sustained observations from vantage points away from the Sun-Earth line. These include observations from the far side of the Sun, at high latitudes including over the solar poles, or from near-quadrature angles relative to the Earth (e.g., the Sun-Earth L4 and L5 Lagrangian points). Such observations fill known holes in our scientific understanding of the three-dimensional, time-evolving Sun and heliosphere, and have the potential to open new frontiers through discoveries enabled by novel viewpoints.

Solar prominences are structures of importance because of their role in polar field reversal. We study the long-term variation of the time latitude distribution of solar prominences in this article. To accomplish this, we primarily used the digitised disc-blocked Ca II K spectroheliograms as recorded from Kodaikanal Solar Observatory for the period of 1906 -- 2002. For improving the data statistics we included full disc H_alpha images from Meudon and Kanzelhohe Observatory which are available after 1980. We developed an automated technique to identify the latitudinal locations of prominences in daily images from all three datasets. Derived time-latitude distribution clearly depicted pole-ward migration of prominence structures for 10 cycles (15-24). Unlike previous studies, we separated the rate of pole-ward migration during on-set and near pole, using piece-wise linear fits. In most cases, we found acceleration in pole-ward migration with the change occurring near +/- 70 degree latitudes. The derived migration rates for such large number of solar cycles can provide important inputs towards understanding polar field build-up process., Comment: 21 pages, 8 figures, 3 tables, published in Earth and Space Science, January, 2020

Spectral observations of the solar transition region (TR) and corona show broadening of spectral lines beyond what is expected from thermal and instrumental broadening. The remaining non-thermal broadening is significant (5-30 km/s) and correlated with the intensity. Here we study spectra of the TR Si IV 1403 Angstrom line obtained at high resolution with the Interface Region Imaging Spectrograph (IRIS). We find that the large improvement in spatial resolution (0.33 arcsec) of IRIS compared to previous spectrographs (2 arcsec) does not resolve the non-thermal line broadening which in most regions remains at pre-IRIS levels of about 20 km/s. This invariance to spatial resolution indicates that the processes behind the broadening occur along the line-of-sight (LOS) and/or on spatial scales (perpendicular to the LOS) smaller than 250 km. Both effects appear to play a role. Comparison with IRIS chromospheric observations shows that, in regions where the LOS is more parallel to the field, magneto-acoustic shocks driven from below impact the TR and can lead to significant non-thermal line broadening. This scenario is supported by MHD simulations. While these do not show enough non-thermal line broadening, they do reproduce the long-known puzzling correlation between non-thermal line broadening and intensity. This correlation is caused by the shocks, but only if non-equilibrium ionization is taken into account. In regions where the LOS is more perpendicular to the field, the prevalence of small-scale twist is likely to play a significant role in explaining the invariance and correlation with intensity., Comment: 7 pages, 5 figures

Spicules have been proposed as significant contributors to the mass and energy balance of the corona. While previous observations have provided a glimpse of short-lived transient brightenings in the corona that are associated with spicules, these observations have been contested and are the subject of a vigorous debate both on the modeling and the observational side. Therefore, it remains unclear whether plasma is heated to coronal temperatures in association with spicules. We use high-resolution observations of the chromosphere and transition region with the Interface Region Imaging Spectrograph (IRIS) and of the corona with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to show evidence of the formation of coronal structures associated with spicular mass ejections and heating of plasma to transition region and coronal temperatures. Our observations suggest that a significant fraction of the highly dynamic loop fan environment associated with plage regions may be the result of the formation of such new coronal strands, a process that previously had been interpreted as the propagation of transient propagating coronal disturbances (PCD)s. Our observations are supported by 2.5D radiative MHD simulations that show heating to coronal temperatures in association with spicules. Our results suggest that heating and strong flows play an important role in maintaining the substructure of loop fans, in addition to the waves that permeate this low coronal environment., Comment: 9 pages, 5 figures

Rieger-type periodicity has been detected in different activity indices over many solar cycles. It was recently shown that the periodicity correlates with solar activity having a shorter period during stronger cycles. Solar activity level is generally asymmetric between northern and southern hemispheres, which could suggest the presence of a similar behavior in the Rieger-type periodicity. We analyse the sunspot area/number and the total magnetic flux data for northern and southern hemispheres during solar cycles 19-23 which had remarkable north-south asymmetry. Using wavelet analysis of sunspot area and number during the north-dominated cycles (19-20) we obtained the periodicity of 160-165 days in the stronger northern hemisphere and 180-190 days in the weaker southern hemisphere. On the other hand, south-dominated cycles (21-23) display the periodicity of 155-160 days in the stronger southern hemisphere and 175-188 days in the weaker northern hemisphere. Therefore, the Rieger-type periodicity has the north-south asymmetry in sunspot area/number data during solar cycles with strong hemispheric asymmetry. We suggest that the periodicity is caused by magnetic Rossby waves in the internal dynamo layer. Using the dispersion relation of magnetic Rossby waves and observed Rieger periodicity we estimated the magnetic field strength in the layer as 45-49 kG in more active hemispheres (north during the cycles 19-20 and south during the cycles 21-23) and 33-40 kG in weaker hemispheres. The estimated difference in the hemispheric field strength is around 10 kG, which provides a challenge for dynamo models. Total magnetic flux data during the cycle 20-23 reveals no clear north-south asymmetry which needs to be explained in the future., Comment: 22 pages, 7 figures

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., Comment: 5 pages, 5 figures. Submitted ApJL

We present the first observation, analysis and modeling of solar coronal twin jets, which occurred after a preceding jet. Detailed analysis on the kinetics of the preceding jet reveals its blowout-jet nature, which resembles the one studied in Liu et al. 2014. However the erupting process and kinetics of the twin jets appear to be different from the preceding one. In lack of the detailed information on the magnetic fields in the twin jet region, we instead use a numerical simulation using a three-dimensional (3D) MHD model as described in Fang et al. 2014, and find that in the simulation a pair of twin jets form due to reconnection between the ambient open fields and a highly twisted sigmoidal magnetic flux which is the outcome of the further evolution of the magnetic fields following the preceding blowout jet. Based on the similarity between the synthesized and observed emission we propose this mechanism as a possible explanation for the observed twin jets. Combining our observation and simulation, we suggest that with continuous energy transport from the subsurface convection zone into the corona, solar coronal twin jets could be generated in the same fashion addressed above., Comment: 7 pages, 5 figures

In this paper, we present the detailed analysis of recurrent homologous jets originating from an emerging negative magnetic flux at the edge of an Active Region. The observed jets show multi-thermal features. Their evolution shows high consistence with the characteristic parameters of the emerging flux, suggesting that with more free magnetic energy, the eruptions tend to be more violent, frequent and blowout-like. The average temperature, average electron number density and axial speed are found to be similar for different jets, indicating that they should have been formed by plasmas from similar origins. Statistical analysis of the jets and their footpoint region conditions reveals a strong positive relationship between the footpoint-region total 131 {\AA} intensity enhancement and jets' length/width. Stronger linearly positive relationships also exist between the total intensity enhancement/thermal energy of the footpoint regions and jets' mass/kinetic/thermal energy, with higher cross-correlation coefficients. All the above results, together, confirm the direct relationship between the magnetic reconnection and the jets, and validate the important role of magnetic reconnection in transporting large amount of free magnetic energy into jets. It is also suggested that there should be more free energy released during the magnetic reconnection of blowout than of standard jet events., Comment: 9 pages, 7 figures, 1 table

We present a new tool, the Solar Eclipse Image Standardisation and Sequencing (SEISS), developed to process multi-source total solar eclipse images by adjusting them to the same standard of size, resolution, and orientation. Furthermore, by analysing the eclipse images we can determine the relative time between the observations and order them to create a movie of the observed total solar eclipse sequence. We successfully processed images taken at the 14 November 2012 total solar eclipse that occurred in Queensland, Australia, and created a short eclipse proto-movie. The SEISS tool was developed for the Eclipse Megamovie Project (EMP: https://www.eclipsemegamovie.org), with the goal of processing thousands of images taken by the public during solar eclipse events. EMP is a collaboration among multiple institutes aiming to engage and advance the public interest in solar eclipses and the science of the Sun-Earth connection.

The Mg II h&k doublet are two of the primary spectral lines observed by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These lines are tracers of the magnetic and thermal environment that spans from the photosphere to the upper chromosphere. We use a double gaussian model to fit the Mg II h profile for a full-Sun mosaic dataset taken 24-Aug-2014. We use the ensemble of high-quality profile fits to conduct a statistical study on the variability of the line profile as it relates the magnetic structure, dynamics, and center-to-limb viewing angle. The average internetwork profile contains a deeply reversed core and is weakly asymmetric at h2. In the internetwork, we find a strong correlation between h3 wavelength and profile asymmetry as well h1 width and h2 width. The average reversal depth of the h3 core is inversely related to the magnetic field. Plage and sunspots exhibit many profiles which do not contain a reversal. These profiles also occur infrequently in the internetwork. We see indications of magnetically aligned structures in plage and network in statistics associated with the line core, but these structures are not clear or extended in the internetwork. The center-to-limb variations are compared with predictions of semi-empirical model atmospheres. We measure a pronounced limb darkening in the line core which is not predicted by the model. The aim of this work is to provide a comprehensive measurement baseline and preliminary analysis on the observed structure and formation of the Mg II profiles observed by IRIS., Comment: Accepted for publication

We combine observations of the Coronal Multi-channel Polarimeter (CoMP) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to study the characteristic properties of (propagating) Alfvenic motions and quasi-periodic intensity disturbances in polar plumes. This unique combination of instruments highlights the physical richness of the processes taking place at the base of the (fast) solar wind. The (parallel) intensity perturbations with intensity enhancements around 1% have an apparent speed of 120 km/s (in both the 171A and 193A passbands) and a periodicity of 15 minutes, while the (perpendicular) Alfvenic wave motions have a velocity amplitude of 0.5 km/s, a phase speed of 830 km/s, and a shorter period of 5 minutes on the same structures. These observations illustrate a scenario where the excited Alfvenic motions are propagating along an inhomogeneously loaded magnetic field structure such that the combination could be a potential progenitor of the magnetohydrodynamic turbulence required to accelerate the fast solar wind., Comment: 15 pages, 4 figures and 1 table