A new solar signal: Average maximum sunspot magnetic fields independent of activity cycle

ABSTRACT We explore the sensitivity of the frequencies of low-degree solar p modes to near-surface magnetic flux on different spatial scales and strengths, specifically to active regions with strong magnetic fields and ephemeral regions with weak magnetic fields. We also use model reconstructions from the literature to calculate average frequency offsets back to the end of the Maunder minimum. We find that the p-mode frequencies are at least 3 times less sensitive (at 95 per cent confidence) to the ephemeral-region field than they are to the active-region field. Frequency shifts between activity cycle minima and maxima are controlled predominantly by the change of active region flux. Frequency shifts at cycle minima (with respect to a magnetically quiet Sun) are determined largely by the ephemeral flux, and are estimated to have been $0.1\, \rm \mu Hz$ or less over the last few minima. We conclude that at epochs of cycle minimum, frequency shifts due to near-surface magnetic activity are negligible compared to the offsets between observed and model frequencies that arise from inaccurate modelling of the near-surface layers (the so-called surface term). The implication is that this will be the case for other Sun-like stars with similar activity, which has implications for asteroseismic modelling of stars.

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Solar activity cycle influenced by changing magnetic fields

Physics Today ◽

10.1063/pt.5.024158 ◽

2010 ◽

Keyword(s):

Solar Activity ◽

Magnetic Fields ◽

Activity Cycle ◽

Solar Activity Cycle

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Global evolution of solar magnetic fields and prediction of activity cycles

Proceedings of the International Astronomical Union ◽

10.1017/s174392132000071x ◽

2019 ◽

Vol 15 (S354) ◽

pp. 147-156

Author(s):

Irina N. Kitiashvili

Keyword(s):

Solar Activity ◽

Magnetic Fields ◽

Activity Cycle ◽

Dynamo Model ◽

Solar Magnetic Fields ◽

Solar Cycles ◽

Multiscale Dynamics ◽

Activity Cycles ◽

Solar Dynamics ◽

Solar Activity Cycles

AbstractPrediction of solar activity cycles is challenging because physical processes inside the Sun involve a broad range of multiscale dynamics that no model can reproduce and because the available observations are highly limited and cover mostly surface layers. Helioseismology makes it possible to probe solar dynamics in the convective zone, but variations in differential rotation and meridional circulation are currently available for only two solar activity cycles. It has been demonstrated that sunspot observations, which cover over 400 years, can be used to calibrate the Parker-Kleeorin-Ruzmaikin dynamo model, and that the Ensemble Kalman Filter (EnKF) method can be used to link the modeled magnetic fields to sunspot observations and make reliable predictions of a following activity cycle. However, for more accurate predictions, it is necessary to use actual observations of the solar magnetic fields, which are available only for the last four solar cycles. In this paper I briefly discuss the influence of the limited number of available observations on the accuracy of EnKF estimates of solar cycle parameters, the criteria to evaluate the predictions, and application of synoptic magnetograms to the prediction of solar activity.

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Large-scale distribution of magnetic fields, green corona and prominences during an extended activity cycle

Solar Physics ◽

10.1007/bf00154161 ◽

1990 ◽

Vol 128 (1) ◽

pp. 253-259 ◽

Cited By ~ 2

Author(s):

Václav Bumba ◽

Vojtech Rušin ◽

Milan Rybanský

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Activity Cycle

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A straightforward estimation of the maximum sunspot number for cycle 23

Annales Geophysicae ◽

10.1007/s00585-999-0639-7 ◽

1999 ◽

Vol 17 (5) ◽

pp. 639-641

Author(s):

B. Mendoza ◽

J. Ramírez

Keyword(s):

Magnetic Fields ◽

Key Words ◽

Sunspot Number ◽

Solar Minimum ◽

Solar Physics ◽

Annual Number ◽

Precursor Method ◽

Maximum Sunspot

Abstract. Using the annual number of geomagnetically quiet days (aa < 20 γ) for the year after the solar minimum, this precursor method predicts that the maximum sunspot number for cycle 23 will be 140 ± 32, indicating that cycle 23 will be similar to cycles 21 and 22.Key words. Solar physics · astrophysics and astronomy (magnetic fields; general)

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Formation of Coronal Holes and the Global Magnetic Field Distribution

International Astronomical Union Colloquium ◽

10.1017/s025292110002501x ◽

1994 ◽

Vol 144 ◽

pp. 65-67 ◽

Cited By ~ 1

Author(s):

V. Bumba ◽

M. Klvaňa ◽

V. Rušin ◽

M. Rybanský ◽

G. T. Buyukliev

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Coronal Holes ◽

Activity Cycle ◽

Close Relation ◽

Solar Activity Cycle ◽

Cycle Maximum ◽

Global Magnetic Field ◽

Mutual Relations ◽

The Individual

The photoelectric magnetograph of the Ondřejov Observatory was reconstructed in 1990 (Klvaňa and Bumba, 1994; Klvaňaet al, 1994). During 1991 and 1992, several hundred sets of measurements were obtained, mostly in line Fel 5253.47 Å. It has been found that some of the measurements are distributed very favorably around coronal holes, sometimes covering smaller parts and in a few cases even larger parts of their areas.Both 1991 and 1992 were exceptional as regards their relation to the phase of the ending solar activity cycle (No 22): while the period of the secondary cycle maximum (mainly the southern solar hemisphere) took place in 1991, the year 1992 coincided with the initial stage of its declining branch. Since the formation of coronal holes is in close relation to the dynamics of the global distribution of solar magnetic fields, we thought that before starting to investigate the detailed connections of the individual coronal holes with particular local magnetic fields, it might be interesting to study their mutual relations also on a large scale.

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Convection and Irradiance Variations

International Astronomical Union Colloquium ◽

10.1017/s0252921100024787 ◽

1994 ◽

Vol 143 ◽

pp. 280-290

Author(s):

Peter A. Fox ◽

Sabatino Sofia

Keyword(s):

Heat Flux ◽

Magnetic Fields ◽

Active Regions ◽

Activity Cycle ◽

Solar Activity Cycle ◽

Theoretical Work ◽

Total Solar Irradiance ◽

Zone Structure ◽

Spatial And Temporal Scales ◽

Convective Motions

In the outer layers of the Sun (≈ 30% by radius), energy is transported by convection. The nature of the highly stratified and compressible convective flow is determined from the components of the energy flux (internal, kinetic, viscous, magnetic and radiative). Local suppressions or enhancements of any of these components may give rise to measurable changes in the emergent radiation.On the solar surface there is direct evidence for modulation of the emerging heat flux covering a large range in spatial and temporal scales, particularly associated with concentrated magnetic fields (e.g. sunspots, plages). Associated with these surface features is the observation that the characteristics of convective motions are also modified. In the deeper layers, the interaction of convection and magnetic fields will play an important role in readjusting the local emerging heat flux and thus should contribute to the modulation of the total solar irradiance.The task of calculating the response of the convection zone structure to developing active regions, and the solar activity cycle in general is difficult and complex due to the highly non-linear nature of the interaction of convection and magnetic fields. Theoretical work has ranged from empirical and global structure models, all the way to fine scale compressible convection simulations. This paper will highlight some recent theoretical advances that may have a direct bearing on the understanding of solar luminosity and irradiance variations and outline the important problems that must be addressed and what observational constraints may be used.

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Stellar magnetic cycles

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309992523 ◽

2009 ◽

Vol 5 (S264) ◽

pp. 120-129 ◽

Cited By ~ 5

Author(s):

A. F. Lanza

Keyword(s):

Magnetic Fields ◽

Activity Cycle ◽

Solar Activity Cycle ◽

Stellar Structure ◽

Dynamo Action ◽

Time Extension ◽

Hydromagnetic Dynamo ◽

Activity Cycles ◽

Magnetic Cycles ◽

Stellar Magnetic Fields

AbstractThe solar activity cycle is a manifestation of the hydromagnetic dynamo working inside our star. The detection of activity cycles in solar-like stars and the study of their properties allow us to put the solar dynamo in perspective, investigating how dynamo action depends on stellar parameters and stellar structure. Nevertheless, the lack of spatial resolution and the limited time extension of stellar data pose limitations to our understanding of stellar cycles and the possibility to constrain dynamo models. I briefly review some results obtained from disc-integrated proxies of stellar magnetic fields and discuss the new opportunities opened by space-borne photometry made available by MOST, CoRoT, Kepler, and GAIA, and by new ground-based spectroscopic or spectropolarimetric observations. Stellar cycles have a significant impact on the energetic output and circumstellar magnetic fields of late-type active stars which affects the interaction between stars and their planets. On the other hand, a close-in massive planet could affect the activity of its host star. Recent observations provide circumstantial evidence of such an interaction with possible consequences for stellar activity cycles.

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Surface Magnetic Fields during the Solar Activity Cycle

Physics of Solar Variations ◽

10.1007/978-94-010-9633-1_17 ◽

1981 ◽

pp. 131-145

Author(s):

Robert Howard ◽

Barry J. Labonte

Keyword(s):

Solar Activity ◽

Magnetic Fields ◽

Activity Cycle ◽

Solar Activity Cycle

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Helioseismic insights into the generation and evolution of the Sun’s internal magnetic field

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320000630 ◽

2019 ◽

Vol 15 (S354) ◽

pp. 94-106

Author(s):

Anne-Marie Broomhall ◽

René Kiefer

Keyword(s):

Magnetic Fields ◽

Meridional Circulation ◽

Torsional Oscillation ◽

Activity Cycle ◽

Solar Interior ◽

Acoustic Oscillations ◽

Near Surface ◽

Activity Cycles ◽

The Impact ◽

The Relationship

AbstractProperties of helioseismic acoustic oscillations (p modes) are modified by flows and magnetic fields in the solar interior, with frequencies, amplitudes and damping rates all varying systematically through the solar cycle. Crucially, now, we have a long enough baseline of helioseismic data to compare of the different activity cycles. We review recent efforts along these lines, from the impact of near-surface magnetic fields on p-mode frequencies to the evolution of the torsional oscillation and meridional circulation. We show that each activity cycle for which we have helioseismic data is slightly different in terms of the relationship between p mode frequencies and atmospheric proxies of activity, and in terms of the rotation and meridional circulation flows. However, many challenges remain, crucially including our ability to constrain flows and magnetic fields in the deep solar interior.

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