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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., 16 pages, 10 figures - Accepted to appear in Frontiers

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

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., Comment: 27 pages (manuscript) 12 Figures

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.

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

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 takes place in ...

The frequency of major solar eruptions, and their space weather impacts at earth vary with the cycle of solar activity but large amplitude events can occur at any time. Each solar cycle has a disti...

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

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]

To make transformational scientific progress with the space weather enterprise the Sun, Earth, and heliosphere must be studied as a coupled system, comprehensively. Rapid advances were made in the study, and forecasting, of terrestrial meteorology half a century ago that accompanied the dawn of earth observing satellites. Those assets provided a global perspective on the Earth's weather systems and the ability to look ahead of the observer's local time and to. From a heliospheric, or space, weather perspective we have the same fundamental limitation as the terrestrial meteorologists had—by far the majority of our observing assets are tied to the Sun-Earth line—our planet's “local time” with respect to the Sun. This perspective intrinsically limits our ability to “see what is coming around the solar limb” far less to gain any insight into the global patterns of solar weather and how they guide weather throughout the heliosphere. We propose a mission concept—the Heliospheric Meteorology Mission (HMM)—to sample the complete magnetic and thermodynamic state of the heliosphere inside 1AU using a distributed network of deep space hardened smallsats that encompass the Sun. The observations and in situ plasma measurements made by the fleet of HMM smallsats would be collected, and assimilated into current operational space weather models. Further, the HMM measurements would also being used in an nationally coordinated research effort—at the frontier of understanding the coupled heliospheric system—as a means to develop the next generation models required to provide seamless prediction for the geospace environment to protect vital infrastructure and human/robotic explorers throughout the solar system. The HMM mission concept naturally allows for research-motivated technology development that can improve forecast skill.

In 1844 Schwabe discovered that the number of sunspots increased and decreased over a period of about 11 years, that variation became known as the sunspot cycle. Almost eighty years later, Hale described the nature of the Sun's magnetic field, identifying that it takes about 22 years for the Sun's magnetic polarity to cycle. It was also identified that the latitudinal distribution of sunspots resembles the wings of a butterfly showing migration of sunspots in each hemisphere that abruptly start at mid-latitudes towards the Sun's equator over the next 11 years. These sunspot patterns were shown to be asymmetric across the equator. In intervening years, it was deduced that the Sun (and sun-like stars) possess magnetic activity cycles that are assumed to be the physical manifestation of a dynamo process that results from complex circulatory transport processes in the star's interior. Understanding the Sun's magnetism, its origin and its variation, has become a fundamental scientific objective \-- the distribution of magnetism, and its interaction with convective processes, drives various plasma processes in the outer atmosphere. In the past few decades, a range of diagnostic techniques have been employed to systematically study finer scale magnetized objects, and associated phenomena. The patterns discerned became known as the ``Extended Solar Cycle'' (ESC). The patterns of the ESC appeared to extend the wings of the activity butterfly back in time, nearly a decade before the formation of the sunspot pattern, and to much higher solar latitudes. In this short review, we describe their observational patterns of the ESC and discuss possible connections to the solar dynamo as we depart on a multi-national collaboration to investigate the origins of solar magnetism through a blend of archived and contemporary data analysis with the goal of improving solar dynamo understanding and modeling., Comment: 11 Pages; 03 Figures

Rossby waves are a type of global-scale wave that develops in planetary atmospheres, driven by the planet’s rotation1. They propagate westward owing to the Coriolis force, and their characterization enables more precise forecasting of weather on Earth2,3. Despite the massive reservoir of rotational energy available in the Sun’s interior and decades of observational investigation, their solar analogue defies unambiguous identification4–6. Here we analyse a combined set of images obtained by the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) spacecraft between 2011 and 2013 in order to follow the evolution of small bright features, called brightpoints, which are tracers of rotationally driven large-scale convection7. We report the detection of persistent, global-scale bands of magnetized activity on the Sun that slowly meander westward in longitude and display Rossby-wave-like behaviour. These magnetized Rossby waves allow us to make direct connections between decadal-scale solar activity and that on much shorter timescales. Monitoring the properties of these waves, and the wavenumber of the disturbances that they generate, has the potential to yield a considerable improvement in forecast capability for solar activity and related space weather phenomena. Global-scale Rossby waves develop in planets’ atmospheres and influence their weather. Now, similar waves, driven by magnetism, are unambiguously detected on the Sun. They can possibly help the forecasting of solar activity and related space weather.

Recent in situ observations of the solar wind show that charge states (e.g., the O7+/O6+and C6+/C5+abundance ratios) evolved through the extended, deep solar minimum between solar cycles 23 and 24 (i.e., from 2006 to 2009) reflecting cooler electron temperatures in the corona. We extend previous analyses to study the evolution of the coronal electron temperature through the protracted solar minimum and observe not only the reduction in coronal temperature in the cycles 23–24 solar minimum but also a small increase in coronal temperature associated with increasing activity during the “mini maximum” in cycle 24. We use a new model of the interplanetary magnetic flux since 1749 to estimate coronal electron temperatures over more than two centuries. The reduction in coronal electron temperature in the cycles 23–24 protracted solar minimum is similar to reductions observed at the beginning of the Dalton Minimum (∼1805–1840). If these trends continue to reflect the evolution of the Dalton Minimum, we will observe further reductions in coronal temperature in the cycles 24–25 solar minimum. Preliminary indications in 2013 do suggest a further post cycle 23 decline in solar activity. Thus, we extend our understanding of coronal electron temperature using the solar wind scaling law and compare recent reductions in coronal electron temperature in the protracted solar minimum to conditions that prevailed in the Dalton Minimum.

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

As the observational signature of the footprints of solar magnetic field lines open into the heliosphere, coronal holes provide a critical measure of the structure and evolution of these lines. Using a combination of Solar and Heliospheric Observatory / Extreme ultraviolet Imaging Telescope (SOHO/EIT), Solar Dynamics Observatory / Atmospheric Imaging Assembly (SDO/AIA) and Solar Terrestrial Relations Observatory / Extreme Ultraviolet Imager (STEREO/EUVI A/B) extreme ultraviolet (EUV) observations spanning 1996-2015 (nearly two solar cycles), coronal holes are automatically detected and characterized. Coronal hole area distributions show distinct behavior in latitude, defining the domain of polar and low-latitude coronal holes. The northern and southern polar regions show a clear asymmetry, with a lag between hemispheres in the appearance and disappearance of polar coronal holes., Accepted for publication in Solar Physics

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar–heliospheric–planetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March – 16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earth’s mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.

In 2011, three satellites—the Solar-Terrestrial RElations Observatory A & B, and the Solar Dynamics Observatory (SDO)—were in a unique spatial alignment that allowed a 360° view of the Sun. This alignment lasted until 2014, the peak of solar cycle 24. Using extreme ultraviolet images and Hovmoller diagrams, we studied the lifetimes and propagation characteristics of coronal holes (CHs) in longitude over several solar rotations. Our initial results show at least three distinct populations of "low-latitude" or "equatorial" CHs (below latitude). One population rotates in retrograde direction and coincides with a group of long-lived (over sixty days) CHs in each hemisphere. These are typically located between 30° and , and display velocities of ~55 m s−1 slower than the local differential rotation rate. A second, smaller population of CHs rotate prograde, with velocities between ~20 and 45 m s−1. This population is also long-lived, but observed ±10° from the solar equator. A third population of CHs are short-lived (less than two solar rotations), and they appear over a wide range of latitudes (±65°) and exhibit velocities between −140 and 80 m s−1. The CH "butterfly diagram" we developed shows a systematic evolution of the longer-lived holes; however, the sample is too short in time to draw conclusions about possible connections to dynamo-related phenomena. An extension of the present work to the 22 years of the combined SOHO–SDO archives is necessary to understand the contribution of CHs to the decadal-scale evolution of the Sun.

We present a new method of visualizing the solar photospheric magnetic field based on the "Magnetic Range of Influence" (MRoI). The MRoI is a simple realization of the magnetic environment in the photosphere, reflecting the distance required to balance the integrated magnetic field contained in any magnetogram pixel. It provides a new perspective on where sub-terrestrial field lines in a Potential Field Source Surface (PFSS) model connect to the photosphere, and thus the source of Earth-directed solar wind (within the limitations of PFSS models), something that is not usually obvious from a regular synoptic magnetogram. In each of three sample solar rotations, at different phases of the solar cycle, the PFSS footpoint either jumps between isolated areas of high MRoI or moves slowly within one such area. Footpoint motions are consistent with Fisk's interchange reconnection model., Comment: 12 pages, 4 figures, accepted for publication by ApJ Letters

In 1999 May an interval of unusually slow (

The Sun provides the energy necessary to sustain our existence. While the Sun provides for us, it is also capable of taking away. The weather and climatic scales of solar evolution and the Sun-Earth connection are not well understood. There has been tremendous progress in the century since the discovery of solar magnetism - magnetism that ultimately drives the electromagnetic, particulate and eruptive forcing of our planetary system. There is contemporary evidence of a decrease in solar magnetism, perhaps even indicators of a significant downward trend, over recent decades. Are we entering a minimum in solar activity that is deeper and longer than a typical solar minimum, a "grand minimum"? How could we tell if we are? What is a grand minimum and how does the Sun recover? These are very pertinent questions for modern civilization. In this paper we present a hypothetical demonstration of entry and exit from grand minimum conditions based on a recent analysis of solar features over the past 20 years and their possible connection to the origins of the 11(-ish) year solar activity cycle., 9 pages - submitted to Frontiers in Solar and Stellar Physics

Solar magnetism displays a host of variational timescales of which the enigmatic 11-year sunspot cycle is most prominent. Recent work has demonstrated that the sunspot cycle can be explained in terms of the intra- and extra-hemispheric interaction between the overlapping activity bands of the 22-year magnetic polarity cycle. Those activity bands appear to be driven by the rotation of the Sun's deep interior. Here we deduce that activity band interaction can qualitatively explain the ‘Gnevyshev Gap'—a well-established feature of flare and sunspot occurrence. Strong quasi-annual variability in the number of flares, coronal mass ejections, the radiative and particulate environment of the heliosphere is also observed. We infer that this secondary variability is driven by surges of magnetism from the activity bands. Understanding the formation, interaction and instability of these activity bands will considerably improve forecast capability in space weather and solar activity over a range of timescales., The origins of the Sun's periodic activity, such as sunspot cycles, are poorly understood. McIntosh et al. posit that the rotational forcing of the activity bands comprising the 22-year magnetic cycle undergoes shorter-term variations, driving magnetic flux surges that impact solar output on those timescales.

We investigate the nature of turbulent magnetic dissipation in the solar wind. We employ a database describing the spectra of over 800 intervals of interplanetary magnetic field and solar wind measurements recorded by the ACE spacecraft at 1 AU. We focus on the spectral properties of the dissipation range that forms at spacecraft frequencies ≥0.3 Hz and show that while the inertial range at lower frequencies displays a tightly constrained range of spectral indexes, the dissipation range exhibits a broad range of power-law indexes. We show that the explanation for this variation lies with the dependence of the dissipation range spectrum on the rate of energy cascade through the inertial range such that steeper spectral forms result from greater cascade rates.

We correlate the inferred structure of the solar chromospheric plasma topography with in situ solar wind velocity and composition data measured at 1 AU. Diagnostics of atmospheric "depth" in the chromosphere are made for several observing periods in active, coronal hole, and quiet-Sun regions. We demonstrate that the inferred chromospheric diagnostics correlate very strongly with solar wind velocity and inversely with the ratio of ionic oxygen (O+7/O+6) densities. These correlations suggest that the structure of the solar wind is rooted deeper in the outer solar atmosphere than has been previously considered.

A distinctive characteristic of interplanetary magnetic clouds is their rope-like magnetic structure, i.e. , their smoothly-varying helical field lines whose pitch increases from their core to their boundary. Because this regular structure helps to make MCs particularly geo-effective, it is important to understand how it arises. We discuss recent work which relates the magnetic and topological parameters of MCs to associated solar active regions. This work strongly supports the notion that MCs associated with active region eruptions are formed by magnetic reconnection between these regions and their larger-scale surroundings, rather than simple eruption or entrainment of pre-existing structures in the corona or chromosphere. We discuss our findings in the context of other recent works on both the solar and interplanetary sides, including ion composition and various MHD models of magnetic cloud formation. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report the results of two simple studies that seek observational evidence that solar coronal loops are unstable to the MHD kink instability above a certain critical value of the total twist. First, we have used Yohkoh soft X-ray telescope image sequences to measure the shapes of 191 X-ray sigmoids and to determine the histories of eruption (evidenced by cusp and arcade signatures) of their associated active regions. We find that the distribution of sigmoid shapes is quite narrow and the frequency of eruption does not depend significantly on shape. Second, we have used Mees Solar Observatory vector magnetograms to estimate the large-scale total twist of active regions in which flare-related signatures of eruption are observed. We find no evidence of eruption for values of large-scale total twist remotely approaching the threshold for the kink instability.

Coronal holes are regions on the Sun's surface that map the foot-prints of open magnetic field lines. We have developed an automated routine to detect and track boundaries of long-lived coronal holes using full-disk EUV images obtained by SoHO:EIT, SDO:AIA, and STEREO:EUVI. We measure coronal hole areas and magnetic flux in these holes, and compare the measurements with calculations by the PFSS model. It is shown that, from 1996 through 2010, the total area of coronal holes measured with EIT images varies between 5$\%$ and 17$\%$ of the total solar surface area, and the total unsigned open flux varies between $2-5 \times 10^{22}$ Mx. The solar cycle dependence of these measurements are similar to the PFSS results, but the model yields larger hole areas and greater open flux than observed by EIT. The AIA/EUVI measurements from 2010-2013 show coronal hole area coverage of 5-10$\%$ of the total surface area, with significant contribution from low latitudes, which is under-represented by EIT. AIA/EUVI have measured much enhanced open magnetic flux in the range of $2-4 \times 10^{22}$ Mx, which is about twice the flux measured by EIT, and matches with the PFSS calculated open flux, with discrepancies in the location and strength of coronal holes. A detailed comparison between the three measurements (by EIT, AIA-EUVI, and PFSS) indicates that coronal holes in low latitudes contribute significantly to the total open magnetic flux. These low-latitude coronal holes are not well measured with either the He I 10830 line in previous studies, or EIT EUV images; neither are they well captured by the static PFSS model. The enhanced observations from AIA/EUVI allow a more accurate measure of these low latitude coronal holes, and their contribution to open magnetic flux., 13 pages, 13 figures

Sunspots are a canonical marker of the Sun's internal magnetic field which flips polarity every ~22-years. The principal variation of sunspots, an ~11-year variation in number, modulates the amount of magnetic field that pierces the solar surface and drives significant variations in our Star's radiative, particulate and eruptive output over that period. This paper presents observations from the Solar and Heliospheric Observatory and Solar Dynamics Observatory indicating that the 11-year sunspot variation is intrinsically tied it to the spatio-temporal overlap of the activity bands belonging to the 22-year magnetic activity cycle. Using a systematic analysis of ubiquitous coronal brightpoints, and the magnetic scale on which they appear to form, we show that the landmarks of sunspot cycle 23 can be explained by considering the evolution and interaction of the overlapping activity bands of the longer scale variability., 26 pages

Mechanisms for the deposition of heat in the lower coronal plasma are discussed, emphasizing recent attempts to reconcile the —uid and kinetic perspectives. Structures at magnetohydrodynamic (MHD) scales may drive a nonlinear cascade, preferentially exciting high perpendicular wavenumber —uctuations. Relevant dissipative kinetic processes must be identi—ed that can absorb the associated energy —ux. The relationship between the MHD cascade and direct cyclotron absorption, including cyclotron sweep, is discussed. We conclude that for coronal and solar wind parameters the perpendicular cascade cannot be neglected and may be more rapid than cyclotron sweep. Solar wind observational evidence suggests the relevance of the ion inertial scale, which is associated with current sheet thickness during reconnection. We conclude that a signi—cant fraction of dissipation in the corona and solar wind likely proceeds through a perpendicular cascade and small-scale reconnection, coupled to kinetic processes that act at oblique wavevectors. Subject headings: MHDsolar windSun: coronaSun: magnetic —eldsturbulence

In a previous paper we argued that the damping of obliquely propagating kinetic Alfven waves, chiefly by resonant mechanisms, was a likely explanation for the formation of the dissipation range for interplanetary magnetic field fluctuations. This suggestion was based largely on observations of the dissipation range at 1 AU as recorded by the Wind spacecraft. We pursue this suggestion here with both a general examination of the damping of obliquely propagating kinetic Alfven waves and an additional examination of the observations. We explore the damping rates of kinetic Alfven waves under a wide range of interplanetary conditions using numerical solutions of the linearized Maxwell-Vlasov equations and demonstrate that these waves display the nearly isotropic dissipation properties inferred from the previous paper. Using these solutions, we present a simple model to predict the onset of the dissipation range and compare these predictions to the observations. In the process we demonstrate that electron Landau damping plays a significant role in the damping of interplanetary magnetic field fluctuations which leads to significant heating of the thermal electrons.

We examine some implications of inertial range and dissipation range correlation and spectral analyses extracted from 33 intervals of Wind magnetic field data. When field polarity and signatures of cross helicity and magnetic helicity are examined, most of the datasets suggest some role of cyclotron resonant dissipative processes involving thermal protons. We postulate that an active spectral cascade into the dissipation range is balanced by a combination of cyclotron-resonant and non-cyclotron-resonant kinetic dissipation mechanisms, of which only the former induces a magnetic helicity signature. A rate balance theory, constrained by the data, suggests that the ratio of the two mechanisms is of order unity. While highly simplified, this approach appears to account for several observed features, and explains why complete cyclotron absorption, and the corresponding pure magnetic helicity signature, is usually not observed., With 1 figure; accepted by Astrophys. J. Lett., September 1, 1998

We determine the geometry of the fluctuations of the magnetic field at frequencies just above the proton gyrofrequency for the January 10, 1997 CME and the magnetic cloud within. The transverse magnetic fluctuations represent a greater fraction of the magnetic energy than is the case in the typical undisturbed solar wind. The break in the power spectrum that is associated with the the onset of magnetic dissipation falls within the frequency range of interest. The fluctuation geometry is markedly different above and below the spectral break frequency. The inertial range geometry remains unchanged in the cloud with only ∼30% of the energy associated with field-aligned wave vectors. The dissipation range wave vectors are highly oblique to the mean magnetic field B with up to 96% of the energy associated with oblique wave vectors.

The dissipation range for interplanetary magnetic field fluctuations is formed by those fluctuations with spatial scales comparable to the gyroradius or ion inertial length of a thermal ion. It is reasonable to assume that the dissipation range represents the final fate of magnetic energy that is transferred from the largest spatial scales via nonlinear processes until kinetic coupling with the background plasma removes the energy from the spectrum and heats the background distribution. Typically, the dissipation range at 1 AU sets in at spacecraft frame frequencies of a few tenths of a hertz. It is characterized by a steepening of the power spectrum and often demonstrates a bias of the polarization or magnetic helicity spectrum. We examine Wind observations of inertial and dissipation range spectra in an attempt to better understand the processes that form the dissipation range and how these processes depend on the ambient solar wind parameters (interplanetary magnetic field intensity, ambient proton density and temperature, etc.). We focus on stationary intervals with well-defined inertial and dissipation range spectra. Our analysis shows that parallel-propagating waves, such as Alfven waves, are inconsistent with the data. MHD turbulence consisting of a partly slab and partly two-dimensional (2-D) composite geometry is consistent with the observations, while thermal paxticle interactions with the 2-D component may be responsible for the formation of the dissipation range. Kinetic Alfven waves propagating at large angles to the background magnetic field are also consistent with the observations and may form some portion of the 2-D turbulence component.

Recent work has revealed an phenomenological picture of the how the $\sim$11-year sunspot cycle of Sun arises. The production and destruction of sunspots is a consequence of the latitudinal-temporal overlap and interaction of the toroidal magnetic flux systems that belong to the 22-year magnetic activity cycle and are rooted deep in the Sun's convective interior. We present a conceptually simple extension of this work, presenting a hypothesis on how complex active regions can form as a direct consequence of the intra- and extra-hemispheric interaction taking place in the solar interior. Furthermore, during specific portions of the sunspot cycle we anticipate that those complex active regions may be particular susceptible to profoundly catastrophic breakdown---producing flares and coronal mass ejections of most severe magnitude., Comment: 14 pages, 5 figures, accepted to appear in ApJL

Among many other measurable quantities the summer of 2009 saw a considerable low in the radiative output of the Sun that was temporally coincident with the largest cosmic ray flux ever measured at 1AU. A hemispheric asymmetry in magnetic activity is clearly observed and its evolution monitored and the resulting (prolonged) magnetic imbalance must have had a considerable impact on the structure and energetics of the heliosphere. While we cannot uniquely tie the variance and scale of the surface magnetism to the dwindling radiative and particulate output of the star, or the increased cosmic ray flux through the 2009 minimum, the timing of the decline and rapid recovery in early 2010 would appear to inextricably link them. These observations support a picture where the Sun's hemispheres are significantly out of phase with each other. Studying historical sunspot records with this picture in mind shows that the northern hemisphere has been leading since the middle of the last century and that the hemispheric "dominance" has changed twice in the past 130 years. The observations presented give clear cause for concern, especially with respect to our present understanding of the processes that produce the surface magnetism in the (hidden) solar interior - hemispheric asymmetry is the normal state - the strong symmetry shown in 1996 was abnormal. Further, these observations show that the mechanism(s) which create and transport the magnetic flux magnetic flux are slowly changing with time and, it appears, with only loose coupling across the equator such that those asymmetries can persist for a considerable time. As the current asymmetry persists and the basal energetics of the system continue to dwindle we anticipate new radiative and particulate lows coupled with increased cosmic ray fluxes heading into the next solar minimum., Comment: Accepted to appear in the ApJ - 44 pages in referee format

A surprise discovery during the Ulysses flyby of Jupiter was the presence of what have been called null field events in the outer magnetosphere. The signatures are quite distinct from those of the multiple magnetodisk encounters seen closer to the planet. Subsequently, similar events have been identified in both Pioneer and Voyager spacecraft magnetometer data. We propose that these events are formed by the breaking off of material from the outer edge of the magnetodisk current sheet. We discuss their likely origin, evolution, dynamics and internal structure.