Convection and Irradiance Variations

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.

scholarly journals Sensitivity of low-degree solar p modes to active and ephemeral regions: frequency shifts back to the Maunder minimum

2019 ◽  
Vol 489 (1) ◽  
pp. L86-L90 ◽  
Author(s):  
William J Chaplin ◽  
Rachel Howe ◽  
Sarbani Basu ◽  
Yvonne Elsworth ◽  
Timothy W Milbourne ◽  
...  
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Spatial Scales ◽  
Active Regions ◽  
Activity Cycle ◽  
Maunder Minimum ◽  
Field Frequency ◽  
Frequency Shifts ◽  
Near Surface ◽  
Low Degree

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.

Formation of Coronal Holes and the Global Magnetic Field Distribution

1994 ◽  
Vol 144 ◽  
pp. 65-67 ◽  
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.

scholarly journals The spatial relationship between active regions and coronal holes and the occurrence of intense geomagnetic storms throughout the solar activity cycle

1998 ◽  
Vol 16 (1) ◽  
pp. 49-54 ◽  
Author(s):  
S. Bravo ◽  
J. A. L. Cruz-Abeyro ◽  
D. Rojas
Keyword(s):  
Solar Activity ◽  
Coronal Mass Ejections ◽  
Geomagnetic Storms ◽  
Coronal Holes ◽  
Spatial Relationship ◽  
Active Regions ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Frequency Of Occurrence ◽  
Sunspot Maximum

Abstract. We study the annual frequency of occurrence of intense geomagnetic storms (Dst < –100 nT) throughout the solar activity cycle for the last three cycles and find that it shows different structures. In cycles 20 and 22 it peaks during the ascending phase, near sunspot maximum. During cycle 21, however, there is one peak in the ascending phase and a second, higher, peak in the descending phase separated by a minimum of storm occurrence during 1980, the sunspot maximum. We compare the solar cycle distribution of storms with the corresponding evolution of coronal mass ejections and flares. We find that, as the frequency of occurrence of coronal mass ejections seems to follow very closely the evolution of the sunspot number, it does not reproduce the storm profiles. The temporal distribution of flares varies from that of sunspots and is more in agreement with the distribution of intense geomagnetic storms, but flares show a maximum at every sunspot maximum and cannot then explain the small number of intense storms in 1980. In a previous study we demonstrated that, in most cases, the occurrence of intense geomagnetic storms is associated with a flaring event in an active region located near a coronal hole. In this work we study the spatial relationship between active regions and coronal holes for solar cycles 21 and 22 and find that it also shows different temporal evolution in each cycle in accordance with the occurrence of strong geomagnetic storms; although there were many active regions during 1980, most of the time they were far from coronal holes. We analyse in detail the situation for the intense geomagnetic storms in 1980 and show that, in every case, they were associated with a flare in one of the few active regions adjacent to a coronal hole.

Revisiting the building blocks of solar magnetic fields by GREGOR

2019 ◽  
Vol 15 (S354) ◽  
pp. 38-41
Author(s):  
Dominik Utz ◽  
Christoph Kuckein ◽  
Jose Iván Campos Rozo ◽  
Sergio Javier González Manrique ◽  
Horst Balthasar ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Active Regions ◽  
Building Blocks ◽  
Solar Telescope ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Crucial Importance ◽  
Spatial And Temporal Scales ◽  
Wide Range ◽  
Formation And Evolution

AbstractThe Sun is our dynamic host star due to its magnetic fields causing plentiful of activity in its atmosphere. From high energetic flares and coronal mass ejections (CMEs) to lower energetic phenomena such as jets and fibrils. Thus, it is of crucial importance to learn about formation and evolution of solar magnetic fields. These fields cover a wide range of spatial and temporal scales, starting on the larger end with active regions harbouring complex sunspots, via isolated pores, down to the smallest yet resolved elements – so-called magnetic bright points (MBPs). Here, we revisit the various manifestations of solar magnetic fields by the largest European solar telescope in operation, the 1.5-meter GREGOR telescope. We show images from the High-resolution Fast Imager (HiFI) and spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS). Besides, we outline resolved convective features inside the larger structures – so-called light-bridges occurring on large to mid-sized scales.

scholarly journals Stellar magnetic cycles

2009 ◽  
Vol 5 (S264) ◽  
pp. 120-129 ◽  
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.

scholarly journals Cycles and cycle modulations

2011 ◽  
Vol 7 (S286) ◽  
pp. 37-48 ◽  
Author(s):  
Axel Brandenburg ◽  
Gustavo Guerrero
Keyword(s):  
Solar Activity ◽  
Coriolis Force ◽  
Three Dimensional ◽  
Active Regions ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Magnetic Pressure ◽  
Scale Separation ◽  
Limited Scale

AbstractSome selected concepts of the solar activity cycle are reviewed. Cycle modulations through a stochastic α effect are being identified with limited scale separation ratios. Three-dimensional turbulence simulations with helicity and shear are compared at two different scale separation ratios. In both cases the level of fluctuations shows relatively little variation with the dynamo cycle. Prospects for a shallow origin of sunspots are discussed in terms of the negative effective magnetic pressure instability. Tilt angles of bipolar active regions are discussed as a consequence of shear rather than the Coriolis force.

Corotational solar streams and cosmic-ray diurnal anisotropy

1991 ◽  
Vol 69 (8-9) ◽  
pp. 981-983
Author(s):  
A. G. Ananth ◽  
D. Venkatesan
Keyword(s):  
Solar Activity ◽  
Magnetic Fields ◽  
Geomagnetic Activity ◽  
Cosmic Ray ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Detailed Comparison ◽  
Secondary Peak ◽  
Solar Magnetic Fields ◽  
Diurnal Anisotropy

A detailed comparison of the behavior of cosmic-ray diurnal anisotropy with the solar activity cycle indicates that the amplitude of the diurnal anisotropy is significantly modulated by the corotational streams that produce the secondary peak in geomagnetic activity. However, the time of the maximum of diurnal anisotropy does not show any systematic changes with solar activity but indicates a shift towards earlier hours (~12:00 LT), corresponding to the reversal of polarity of solar magnetic fields.

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