scholarly journals Magnetic flux transport of decaying active regions and enhanced magnetic network

Solar Physics ◽  
1991 ◽  
Vol 131 (1) ◽  
pp. 53-68 ◽  
Author(s):  
Haimin Wang ◽  
Harold Zirin ◽  
Guoxiang Ai
Keyword(s):  
Magnetic Flux ◽  
Active Regions ◽  
Flux Transport ◽  
Magnetic Network

scholarly journals Predicting cycle 24 using various dynamo-based tools

2008 ◽  
Vol 26 (2) ◽  
pp. 259-267 ◽  
Author(s):  
M. Dikpati
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Active Regions ◽  
Flux Transport ◽  
Delayed Onset ◽  
Drift Speed ◽  
Sensitivity Tests ◽  
The Mean ◽  
Cycle 24

Abstract. Various dynamo-based techniques have been used to predict the mean solar cycle features, namely the amplitude and the timings of onset and peak. All methods use information from previous cycles, including particularly polar fields, drift-speed of the sunspot zone to the equator, and remnant magnetic flux from the decay of active regions. Polar fields predict a low cycle 24, while spot zone migration and remnant flux both lead to predictions of a high cycle 24. These methods both predict delayed onset for cycle 24. We will describe how each of these methods relates to dynamo processes. We will present the latest results from our flux-transport dynamo, including some sensitivity tests and how our model relates to polar fields and spot zone drift methods.

scholarly journals Modeling Coronal Response in Decaying Active Regions with Magnetic Flux Transport and Steady Heating

2017 ◽  
Vol 846 (2) ◽  
pp. 165 ◽  
Author(s):  
Ignacio Ugarte-Urra ◽  
Harry P. Warren ◽  
Lisa A. Upton ◽  
Peter R. Young
Keyword(s):  
Magnetic Flux ◽  
Active Regions ◽  
Flux Transport

Simulations of magnetic-flux transport in solar active regions

Solar Physics ◽  
1985 ◽  
Vol 102 (1-2) ◽  
pp. 41-49 ◽  
Author(s):  
C. R. DeVore ◽  
N. R. Sheeley ◽  
J. P. Boris ◽  
T. R. Young ◽  
K. L. Harvey
Keyword(s):  
Magnetic Flux ◽  
Active Regions ◽  
Flux Transport ◽  
Solar Active Regions

scholarly journals MAGNETIC FLUX TRANSPORT AND THE LONG-TERM EVOLUTION OF SOLAR ACTIVE REGIONS

2015 ◽  
Vol 815 (2) ◽  
pp. 90 ◽  
Author(s):  
Ignacio Ugarte-Urra ◽  
Lisa Upton ◽  
Harry P. Warren ◽  
David H. Hathaway
Keyword(s):  
Magnetic Flux ◽  
Active Regions ◽  
Long Term Evolution ◽  
Flux Transport ◽  
Term Evolution ◽  
Solar Active Regions

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

Magnetic Flux Transport on the Sun

Science ◽  
1989 ◽  
Vol 245 (4919) ◽  
pp. 712-718 ◽  
Author(s):  
Y. -M. WANG ◽  
A. G. NASH ◽  
N. R. SHEELEY
Keyword(s):  
Magnetic Flux ◽  
The Sun ◽  
Flux Transport

scholarly journals How faculae and network relate to sunspots, and the implications for solar and stellar brightness variations

2020 ◽  
Vol 639 ◽  
pp. A139 ◽  
Author(s):  
K. L. Yeo ◽  
S. K. Solanki ◽  
N. A. Krivova
Keyword(s):  
Magnetic Flux ◽  
Active Regions ◽  
Total Solar Irradiance ◽  
Area Ratio ◽  
Sunspot Area ◽  
Activity Levels ◽  
Network Coverage ◽  
Chromospheric Emission ◽  
Activity Dependence ◽  
The Relationship

Context. How global faculae and network coverage relates to that of sunspots is relevant to the brightness variations of the Sun and Sun-like stars. Aims. We aim to extend and improve on earlier studies that established that the facular-to-sunspot-area ratio diminishes with total sunspot coverage. Methods. Chromospheric indices and the total magnetic flux enclosed in network and faculae, referred to here as “facular indices”, are modulated by the amount of facular and network present. We probed the relationship between various facular and sunspot indices through an empirical model, taking into account how active regions evolve and the possible non-linear relationship between plage emission, facular magnetic flux, and sunspot area. This model was incorporated into a model of total solar irradiance (TSI) to elucidate the implications for solar and stellar brightness variations. Results. The reconstruction of the facular indices from the sunspot indices with the model presented here replicates most of the observed variability, and is better at doing so than earlier models. Contrary to recent studies, we found the relationship between the facular and sunspot indices to be stable over the past four decades. The model indicates that, like the facular-to-sunspot-area ratio, the ratio of the variation in chromospheric emission and total network and facular magnetic flux to sunspot area decreases with the latter. The TSI model indicates the ratio of the TSI excess from faculae and network to the deficit from sunspots also declines with sunspot area, with the consequence being that TSI rises with sunspot area more slowly than if the two quantities were linearly proportional to one another. This explains why even though solar cycle 23 is significantly weaker than cycle 22, TSI rose to comparable levels over both cycles. The extrapolation of the TSI model to higher activity levels indicates that in the activity range where Sun-like stars are observed to switch from growing brighter with increasing activity to becoming dimmer instead, the activity-dependence of TSI exhibits a similar transition. This happens as sunspot darkening starts to rise more rapidly with activity than facular and network brightening. This bolsters the interpretation of this behaviour of Sun-like stars as the transition from a faculae-dominated to a spot-dominated regime.

scholarly journals Impact of nonlinear surface inflows into activity belts on the solar dynamo

2020 ◽  
Vol 10 ◽  
pp. 62
Author(s):  
Melinda Nagy ◽  
Alexandre Lemerle ◽  
Paul Charbonneau
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Activity Cycle ◽  
Surface Flux ◽  
Meridional Flow ◽  
Cycle Model ◽  
Flux Transport ◽  
Bona Fide ◽  
Nonlinear Surface ◽  
The Impact

We examine the impact of surface inflows into activity belts on the operation of solar cycle models based on the Babcock–Leighton mechanism of poloidal field regeneration. Towards this end we introduce in the solar cycle model of Lemerle & Charbonneau (2017. ApJ 834: 133) a magnetic flux-dependent variation of the surface meridional flow based on the axisymmetric inflow parameterization developped by Jiang et al. (2010. ApJ 717: 597). The inflow dependence on emerging magnetic flux thus introduces a bona fide nonlinear backreaction mechanism in the dynamo loop. For solar-like inflow speeds, our simulation results indicate a decrease of 10–20% in the strength of the global dipole building up at the end of an activity cycle, in agreement with earlier simulations based on linear surface flux transport models. Our simulations also indicate a significant stabilizing effect on cycle characteristics, in that individual cycle amplitudes in simulations including inflows show less scatter about their mean than in the absence of inflows. Our simulations also demonstrate an enhancement of cross-hemispheric coupling, leading to a significant decrease in hemispheric cycle amplitude asymmetries and temporal lag in hemispheric cycle onset. Analysis of temporally extended simulations also indicate that the presence of inflows increases the probability of cycle shutdown following an unfavorable sequence of emergence events. This results ultimately from the lower threshold nonlinearity built into our solar cycle model, and presumably operating in the sun as well.

scholarly journals Observations of flux rope formation prior to coronal mass ejections

2013 ◽  
Vol 8 (S300) ◽  
pp. 209-214 ◽  
Author(s):  
Lucie M. Green ◽  
Bernhard Kliem
Keyword(s):  
Magnetic Flux ◽  
Magnetic Structure ◽  
Solar Atmosphere ◽  
Coronal Mass Ejections ◽  
Flux Rope ◽  
Active Regions ◽  
Magnetic Configuration ◽  
Magnetic Flux Rope ◽  
Source Regions ◽  
Flux Ropes

AbstractUnderstanding the magnetic configuration of the source regions of coronal mass ejections (CMEs) is vital in order to determine the trigger and driver of these events. Observations of four CME productive active regions are presented here, which indicate that the pre-eruption magnetic configuration is that of a magnetic flux rope. The flux ropes are formed in the solar atmosphere by the process known as flux cancellation and are stable for several hours before the eruption. The observations also indicate that the magnetic structure that erupts is not the entire flux rope as initially formed, raising the question of whether the flux rope is able to undergo a partial eruption or whether it undergoes a transition in specific flux rope configuration shortly before the CME.

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