A Stellar Perspective on the Magnetic Future of the Sun

2018 ◽  
Vol 13 (S340) ◽  
pp. 213-216
Author(s):  
Travis S. Metcalfe
Keyword(s):  
Solar Cycle ◽  
Rotation Rate ◽  
Magnetic Transition ◽  
The Sun ◽  
Magnetic Cycle ◽  
Solar Magnetic Cycle ◽  
Mount Wilson Observatory ◽  
Activity Cycles ◽  
Transitional Phase ◽  
Shed Light

AbstractAfter decades of effort, the solar magnetic cycle is exceptionally well characterized, but it remains poorly understood. Pioneering work at the Mount Wilson Observatory demonstrated that other Sun-like stars also show regular activity cycles, and identified two distinct relationships between the rotation rate and the length of the cycle. The solar cycle appears to be an outlier, falling between the two stellar relationships, potentially threatening the very foundation of the solar-stellar connection. Recent discoveries emerging from NASA’s Kepler space telescope have started to shed light on this perplexing result, suggesting that the Sun’s rotation rate and magnetic field are currently in a transitional phase that occurs in all middle-aged stars. We have recently identified the manifestation of this magnetic transition in the best available data on stellar cycles. These observations suggest that the solar cycle is currently growing longer on stellar evolutionary timescales, and that the global dynamo may shut down entirely sometime in the next 0.8-2.4 Gyr. Future tests of this hypothesis will come from ground-based activity monitoring of Kepler targets that span the magnetic transition, and from asteroseismology with the TESS mission to determine precise masses and ages for bright stars with known cycles.

scholarly journals Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude

Solar Physics ◽  
2020 ◽  
Vol 295 (12) ◽  
Author(s):  
Scott W. McIntosh ◽  
Sandra Chapman ◽  
Robert J. Leamon ◽  
Ricky Egeland ◽  
Nicholas W. Watkins
Keyword(s):  
Solar Cycle ◽  
Sunspot Number ◽  
Sunspot Cycle ◽  
Periodic Variation ◽  
Magnetic Activity ◽  
The Sun ◽  
Magnetic Cycle ◽  
Hilbert Transforms ◽  
Observational Astronomy ◽  
Activity Cycles

AbstractThe 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, has stimulated 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 Solar 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 Solar Cycle 25 magnitude.

scholarly journals Rotation Rate of Active Nests on the Sun

1993 ◽  
Vol 141 ◽  
pp. 504-506
Author(s):  
Lidia Van Driel-Gesztelyi ◽  
ED B.J. Van Der Zalm ◽  
Cornelis Zwaan
Keyword(s):  
Solar Cycle ◽  
Short Duration ◽  
Rotation Rate ◽  
The Sun ◽  
Group Position ◽  
Position Data ◽  
Sunspot Groups

AbstractWe analyse Greenwich sunpot group position data for one solar cycle (1952-1963) in order to study the rotation rate of clusters of sunspot groups, so-called active nests. We find that the latitude-dependent rotation rate of nests shows an intrinsic spread. This spread appears to be caused by extensive and dense clusters of sunspot nests (superclusters or nested nests), and by very compact single nests of short duration. The ‘best’ rotation rate is defined as the rate at which the highest number of sunspot groups appear to form nests. This latitude-dependent best rotation is close to the rotation rate of individual recurrent sunspots, although nests seem to rotate slightly more rigidly than sunspot groups.

scholarly journals Quasi-periodic changes in the 3D solar anisotropy of Galactic cosmic rays for 1965–2014

2017 ◽  
Vol 609 ◽  
pp. A32 ◽  
Author(s):  
R. Modzelewska ◽  
M. V. Alania
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Activity ◽  
Solar Cycle ◽  
Cosmic Rays ◽  
Ecliptic Plane ◽  
Galactic Cosmic Rays ◽  
Magnetic Cycle ◽  
The North ◽  
Solar Magnetic Cycle

Aims. We study features of the 3D solar anisotropy of Galactic cosmic rays (GCR) for 1965−2014 (almost five solar cycles, cycles 20−24). We analyze the 27-day variations of the 2D GCR anisotropy in the ecliptic plane and the north-south anisotropy normal to the ecliptic plane. We study the dependence of the 27-day variation of the 3D GCR anisotropy on the solar cycle and solar magnetic cycle. We demonstrate that the 27-day variations of the GCR intensity and anisotropy can be used as an important tool to study solar wind, solar activity, and heliosphere. Methods. We used the components Ar, Aϕ and At of the 3D GCR anisotropy that were found based on hourly data of neutron monitors (NMs) and muon telescopes (MTs) using the harmonic analyses and spectrographic methods. We corrected the 2D diurnal (~24-h) variation of the GCR intensity for the influence of the Earth magnetic field. We derived the north-south component of the GCR anisotropy based on the GG index, which is calculated as the difference in GCR intensities of the Nagoya multidirectional MTs. Results. We show that the behavior of the 27-day variation of the 3D anisotropy verifies a stable long-lived active heliolongitude on the Sun. This illustrates the usefulness of the 27-day variation of the GCR anisotropy as a unique proxy to study solar wind, solar activity, and heliosphere. We distinguish a tendency of the 22-yr changes in amplitude of the 27-day variation of the 2D anisotropy that is connected with the solar magnetic cycle. We demonstrate that the amplitudes of the 27-day variation of the north-south component of the anisotropy vary with the 11-yr solar cycle, but a dependence of the solar magnetic polarity can hardly be recognized. We show that the 27-day recurrences of the GG index and the At component are highly positively correlated, and both are highly correlated with the By component of the heliospheric magnetic field.

Coronal Large-Scale Structure in Odd and Even 11-Year Cycles

1994 ◽  
Vol 144 ◽  
pp. 96
Author(s):  
V. I. Makarov ◽  
V. P. Mikhailutsa ◽  
M. P. Fatianov ◽  
T. V. Stepanova
Keyword(s):  
Large Scale ◽  
Radial Direction ◽  
Solar Magnetic Field ◽  
Essential Difference ◽  
The Sun ◽  
High Latitudes ◽  
Solar Cycles ◽  
Magnetic Cycle ◽  
Solar Magnetic Cycle ◽  
Odd Cycles

AbstractObservations of 22 solar eclipses (1914-1991) have been processed. Radial deviations of streamers in the polar and equatorial zones of the Sun in odd and even solar cycles have been studied. An essential difference of the degree of non-radiality of coronal rays at the same latitudes in odd and even cycles has been found. Deviations from the radial direction of streamers are large in the polar zones in the epoch of the maxima of even cycles and in the equatorial zones at the minima of odd cycles. Deviations from radiality at high latitudes are observed mainly in the poleward direction. The results obtained are interpreted in terms of a new model of the cycle, in which the properties of the solar magnetic field depend on the phase of a 22-year solar magnetic cycle.

Mechanism of Cyclically Polarity Reversing Solar Magnetic Cycle as a Cosmic Dynamo

2000 ◽  
Vol 179 ◽  
pp. 365-371
Author(s):  
Hirokazu Yoshimura
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Convection Zone ◽  
Dimensional Space ◽  
Solar Dynamo ◽  
Magnetic Cycle ◽  
Plasma Flows ◽  
Flux Tubes ◽  
Solar Magnetic Cycle ◽  
Dynamo Mechanism

Abstractwe briefly describe historical development of the concept of solar dynamo mechanism that generates electric current and magnetic field by plasma flows inside the solar convection zone. The dynamo is the driver of the cyclically polarity reversing solar magnetic cycle. The reversal process can easily and visually be understood in terms of magnetic field line stretching and twisting and folding in three-dimensional space by plasma flows of differential rotation and global convection under influence of Coriolis force. This process gives rise to formation of a series of huge magnetic flux tubes that propagate along iso-rotation surfaces inside the convection zone. Each of these flux tubes produces one solar cycle. We discuss general characteristics of any plasma flows that can generate magnetic field and reverse the polarity of the magnetic field in a rotating body in the Universe. We also mention a list of problems which are currently being disputed concerning the solar dynamo mechanism together with observational evidences that are to be constraints as well as verifications of any solar cycle dynamo theories of short and long term behaviors of the Sun, particularly time variations of its magnetic field, plasma flows, and luminosity.

scholarly journals Starspot rotation rates versus activity cycle phase: Butterfly diagrams of Kepler stars are unlike that of the Sun

2019 ◽  
Vol 622 ◽  
pp. A85 ◽  
Author(s):  
M. B. Nielsen ◽  
L. Gizon ◽  
R. H. Cameron ◽  
M. Miesch
Keyword(s):  
Effective Temperature ◽  
Rotation Rate ◽  
Activity Cycle ◽  
Magnetic Activity ◽  
Activity Level ◽  
The Sun ◽  
Rotation Rates ◽  
Rotation Periods ◽  
Activity Cycles ◽  
The Mean

Context. During the solar magnetic activity cycle the emergence latitudes of sunspots change, leading to the well-known butterfly diagram. This phenomenon is poorly understood for other stars since starspot latitudes are generally unknown. The related changes in starspot rotation rates caused by latitudinal differential rotation can, however, be measured. Aims. Using the set of 3093 Kepler stars with measured activity cycles, we aim to study the temporal change in starspot rotation rates over magnetic activity cycles, and how this relates to the activity level, the mean rotation rate of the star, and its effective temperature. Methods. We measured the photometric variability as a proxy for the magnetic activity and the spot rotation rate in each quarter over the duration of the Kepler mission. We phase-folded these measurements with the cycle period. To reduce random errors, we performed averages over stars with comparable mean rotation rates and effective temperature at fixed activity-cycle phases. Results. We detect a clear correlation between the variation of activity level and the variation of the starspot rotation rate. The sign and amplitude of this correlation depends on the mean stellar rotation and – to a lesser extent – on the effective temperature. For slowly rotating stars (rotation periods between 15 − 28 days), the starspot rotation rates are clearly anti-correlated with the level of activity during the activity cycles. A transition is observed around rotation periods of 10 − 15 days, where stars with an effective temperature above 4200 K instead show positive correlation. Conclusions. Our measurements can be interpreted in terms of a stellar “butterfly diagram”, but these appear different from that of the Sun since the starspot rotation rates are either in phase or anti-phase with the activity level. Alternatively, the activity cycle periods observed by Kepler are short (around 2.5 years) and may therefore be secondary cycles, perhaps analogous to the solar quasi-biennial oscillations.

Latitudinal dependence of supergranular Area and Fractal dimension

2018 ◽  
Vol 2 (1) ◽  
Author(s):  
Paniveni Udayashankar
Keyword(s):  
Fractal Dimension ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Convection Zone ◽  
Magnetic Activity ◽  
The Sun ◽  
Physical Conditions ◽  
Quiet Region ◽  
Latitudinal Dependence ◽  
Shed Light

Abstract: A dependence of the area of supergranular cells with respect to the Latitude is studied and it is found that the cells are situated symmetrically about the ±250 latitude.Fractal dimension of the supergranular cells also shows a marginal latitudinal dependence, variation being in the range 1.6–1.7 in the latitudinal limits of ±300. Fractal dimension D for supergranulation is obtained according to the relation P ∝ AD/2 where ‘A is the area and ‘P’ is the perimeter of the supergranular cells. A difference in the fractal dimension between the active and quiet region cells is noted which is conjectured to be due to the magnetic activity level.Supergranular cells are essentially a manifestation of convective phenomena. They can shed light on the physical conditions in the convection zone of the Sun. Moreover, supergranules play a key role in the transport and dispersal of magnetic fields as it is an important step in our quest to understand the solar cycle.

scholarly journals Does a Spin–Orbit Coupling Between the Sun and the Jovian Planets Govern the Solar Cycle?

2008 ◽  
Vol 25 (2) ◽  
pp. 85-93 ◽  
Author(s):  
I. R. G. Wilson ◽  
B. D. Carter ◽  
I. A. Waite
Keyword(s):  
Solar Cycle ◽  
Rotation Rate ◽  
Orbital Motion ◽  
Meridional Flow ◽  
Orbit Coupling ◽  
Coupling Mechanism ◽  
The Sun ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Jovian Planets

AbstractWe present evidence to show that changes in the Sun's equatorial rotation rate are synchronized with changes in its orbital motion about the barycentre of the Solar System. We propose that this synchronization is indicative of a spin–orbit coupling mechanism operating between the Jovian planets and the Sun. However, we are unable to suggest a plausible underlying physical cause for the coupling. Some researchers have proposed that it is the period of the meridional flow in the convective zone of the Sun that controls both the duration and strength of the Solar cycle. We postulate that the overall period of the meridional flow is set by the level of disruption to the flow that is caused by changes in Sun's equatorial rotation speed. Based on our claim that changes in the Sun's equatorial rotation rate are synchronized with changes in the Sun's orbital motion about the barycentre, we propose that the mean period for the Sun's meridional flow is set by a Synodic resonance between the flow period (∼22.3 yr), the overall 178.7-yr repetition period for the solar orbital motion, and the 19.86-yr synodic period of Jupiter and Saturn.

scholarly journals Shapes of stellar activity cycles

2020 ◽  
Vol 638 ◽  
pp. A69
Author(s):  
T. Willamo ◽  
T. Hackman ◽  
J. J. Lehtinen ◽  
M. J. Käpylä ◽  
N. Olspert ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Large Scale ◽  
Magnetic Activity ◽  
The Sun ◽  
Data Set ◽  
Cycle Asymmetry ◽  
Asymmetric Shape ◽  
Activity Cycles ◽  
Magnetohydrodynamic Simulations ◽  
Fast Rise

Context. Magnetic activity cycles are an important phenomenon both in the Sun and other stars. The shape of the solar cycle is commonly characterised by a fast rise and a slower decline, but not much attention has been paid to the shape of cycles in other stars. Aims. Our aim is to study whether the asymmetric shape of the solar cycle is common in other stars as well, and compare the cycle asymmetry to other stellar parameters. We also study the differences in the shape of the solar cycle, depending on the activity indicator that is used. The observations are also compared to simulated activity cycles. Methods. We used the chromospheric Ca II H&K data from the Mount Wilson Observatory HK Project. In this data set, we identified 47 individual cycles from 18 stars. We used the statistical skewness of a cycle as a measure of its asymmetry, and compared this to other stellar parameters. A similar analysis has been performed for magnetic cycles extracted from direct numerical magnetohydrodynamic simulations of solar-type convection zones. Results. The shape of the solar cycle (fast rise and slower decline) is common in other stars as well, although the Sun seems to have particularly asymmetric cycles. Cycle-to-cycle variations are large, but the average shape of a cycle is still fairly well represented by a sinusoid, although this does not take its asymmetry into account. We find only slight correlations between the cycle asymmetry and other stellar parameters. There are large differences in the shape of the solar cycle, depending on the activity indicator that is used. The simulated cycles differ in the symmetry of global simulations that cover the full longitudinal range and are therefore capable of exciting non-axisymmetric large-scale dynamo modes, and wedge simulations that cover a partial extent in longitude, where only axisymmetric large-scale modes are possible. The former preferentially produce positive and the latter negative skewness.

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