scholarly journals Solar and Interplanetary Magnetic Helicity Balance of Active Regions

2005 ◽  
Vol 13 ◽  
pp. 122-123
Author(s):  
Cristina H. Mandrini ◽  
Pascal Démoulin ◽  
Lidia van Driel-Gesztelyi ◽  
Sergio Dasso ◽  
Lucinda M. Green ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Differential Rotation ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Constant Current ◽  
Flux Tubes ◽  
Combining Data ◽  
Free Model ◽  
Linear Force ◽  
The One

AbstractWe analyzed the long-term evolution of two active regions (ARs), NOAA 7978 and 8100, from their emergence through their decay using observations from several instruments on board SoHO (MDI, EIT and LASCO) and Yohkoh/SXT. We computed the evolution of the relative coronal magnetic helicity from one central meridian passage to the next, combining data from MDI and SXT with linear force-free models of the coronal magnetic field. Next, we calculated the injection of helicity by photospheric differential rotation using MDI magnetic maps and a mean differential rotation profile. To estimate the depletion of magnetic helicity we counted all the CMEs of which these ARs were the source, and we evaluated their helicity assuming a one to one correspondence with magnetic clouds (MCs) with an average helicity content; this value was computed for a sample of 18 clouds using a cylindrical linear force-free model. Out of our three helicity estimates (variation of coronal magnetic helicity, injection by differential rotation and ejection via CMEs) the one with the largest uncertainty is the amount of helicity ejected via CMEs. However, we determined, by modeling a particular MC using three different approaches in cylindrical geometry (two force-free models and a non force-free model with constant current), that its magnetic helicity content was nearly independent of the model used to fit in situ field observations (Dasso et al. 2003, in preparation). This result justifies our use of the average magnetic helicity value considering only a single MC model. Comparing the three components in the helicity balance (see Table 1), we find that photospheric differential rotation is a minor contributor to the AR magnetic helicity budget. CMEs carry away at least 10 times more helicity than the one differential rotation can provide. Therefore, the magnetic helicity flux needed in the global balance should come from localized photospheric motions that, at least partially, reflect the emergence of twisted flux tubes. Taking into account the magnetic flux in the ARs and the number of turns that a uniformly twisted flux tube should have to survive its rise through the convection zone, we have found that the total helicity carried away in CMEs is approximately equal to the end-to-end helicity of the flux tubes that formed these two ARs. Therefore, we conclude that most of the helicity ejected in CMEs is generated below the photosphere and emerges with the magnetic flux. Extended versions of this work were published in Demoulin et al. (2002, Astronomy & Astrophys. 382, 650) and in Green et al. (2002, Solar Phys. 208, 43), while in Mandrini et al. (2003, Astrophys. & Space Sci., 290, 319) and van Driel-Gesztelyi et al. (2003, Adv. Space Res., 32, 1855) the helicity computations were revised to include the underestimation of magnetic flux density found in MDI data. After this revision, we confirmed our former results.

scholarly journals Study of helicity properties of peculiar active regions

2009 ◽  
Vol 5 (S264) ◽  
pp. 102-104 ◽  
Author(s):  
M. C. López Fuentes ◽  
C. H. Mandrini ◽  
P. Démoulin
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Active Regions ◽  
Solar Interior ◽  
Magnetic Helicity ◽  
Flux Tubes ◽  
Origin And Evolution ◽  
Magnetic Structures ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

AbstractPeculiar solar active regions (ARs), such as δ-islands and other high tilt bipoles, are commonly associated with the emergence of severely deformed magnetic flux tubes. Therefore, the study of these ARs provides valuable information on the origin and evolution of magnetic structures in the solar interior. Here, we infer the magnetic helicity properties of the flux tubes associated to a set of peculiar ARs by studying the evolution of photospheric magnetograms (SOHO/MDI) and coronal observations (SOHO/EIT and TRACE) in combination with force-free models of the magnetic field. We discuss how our results relate to different models of the evolution of emerging magnetic flux tubes.

scholarly journals Linking Thin Flux Tube MHD Models to Apparent Stellar Surface Activity

2004 ◽  
Vol 219 ◽  
pp. 546-551
Author(s):  
T. Granzer ◽  
K. G. Strassmeier
Keyword(s):  
Magnetic Flux ◽  
Surface Activity ◽  
Flux Tube ◽  
Convection Zone ◽  
Active Regions ◽  
Similar Model ◽  
Flux Tubes ◽  
Stellar Convection ◽  
Magnetic Flux Tubes ◽  
Spot Formation

We model thin magnetic flux tubes as they rise from the bottom of a stellar convection zone to the photosphere. On emergence they form active regions, i.e. star spots. This model was very successfully applied to the solar case, where the simulations where in agreement with the butterfly diagram, Joy's law, and Hale's law. We propose the use of a similar model to describe stellar activity in the more extreme form found on active stars. A comparison between Doppler-images of well-observed pre-MS stars and a theoretically derived probability of star-spot formation as a function of latitude is presented.

scholarly journals Transport of Magnetic Helicity and Dynamics of Solar Active Regions

2005 ◽  
Vol 13 ◽  
pp. 117-118 ◽  
Author(s):  
M. K. Georgoulis ◽  
B. J. LaBonte ◽  
D. M. Rust
Keyword(s):  
Time Series ◽  
Active Region ◽  
Lower Limit ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Solar Active Regions ◽  
Linear Force

AbstractWe introduce a method to calculate the magnetic helicity density in a given active-region vector magnetogram, and a lower limit of it, based on a linear force-free (Iff) approximation. Moreover, we provide a lower limit of the total magnetic helicity in the active region (AR). A time series of magnetograms can be used to calculate the rate of helicity transport. The results can be then correlated with manifestations of the dynamical activity in ARs, such as flares and filament eruptions.

scholarly journals Distinguishing between flaring and nonflaring active regions

2020 ◽  
Vol 639 ◽  
pp. A44
Author(s):  
Soumitra Hazra ◽  
Gopal Sardar ◽  
Partha Chowdhury
Keyword(s):  
Active Region ◽  
Magnetic Flux ◽  
Time Evolution ◽  
Large Scale ◽  
Learning Algorithm ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Magnetic Parameters ◽  
Solar Eruptions ◽  
Very High

Context. Large-scale solar eruptions significantly affect space weather and damage space-based human infrastructures. It is necessary to predict large-scale solar eruptions; it will enable us to protect the vulnerable infrastructures of our modern society. Aims. We investigate the difference between flaring and nonflaring active regions. We also investigate whether it is possible to forecast a solar flare. Methods. We used photospheric vector magnetogram data from the Solar Dynamic Observatory’s Helioseismic Magnetic Imager to study the time evolution of photospheric magnetic parameters on the solar surface. We built a database of flaring and nonflaring active regions observed on the solar surface from 2010 to 2017. We trained a machine-learning algorithm with the time evolution of these active region parameters. Finally, we estimated the performance obtained from the machine-learning algorithm. Results. The strength of some magnetic parameters such as the total unsigned magnetic flux, the total unsigned magnetic helicity, the total unsigned vertical current, and the total photospheric magnetic energy density in flaring active regions are much higher than those of the non-flaring regions. These magnetic parameters in a flaring active region evolve fast and are complex. We are able to obtain a good forecasting capability with a relatively high value of true skill statistic. We also find that time evolution of the total unsigned magnetic helicity and the total unsigned magnetic flux provides a very high ability of distinguishing flaring and nonflaring active regions. Conclusions. We can distinguish a flaring active region from a nonflaring region with good accuracy. We confirm that there is no single common parameter that can distinguish all flaring active regions from the nonflaring regions. However, the time evolution of the top two magnetic parameters, the total unsigned magnetic flux and the total unsigned magnetic helicity, have a very high distinguishing capability.

scholarly journals A Model of Solar X-ray Bright Points and Ephemeral Active Regions

1979 ◽  
Vol 32 (6) ◽  
pp. 671 ◽  
Author(s):  
JH Piddington
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Large Scale ◽  
Flux Rope ◽  
Active Regions ◽  
Activity Cycle ◽  
Solar Magnetic Fields ◽  
Flux Tubes ◽  
X Ray ◽  
Field System

Solar ephemeral active regions may provide a larger amount of emerging magnetic flux than the active regions themselves, and the origin and disposal of this flux pose problems. The related X-ray bright points are a major feature of coronal dynamics, and the two phenomena may entail a revision of our ideas of the activity cycle. A new large-scale subsurface magnetic field system has been suggested, but it is shown that such a system is neither plausible nor necessary. The emerging magnetic bipoles merely represent loops in pre-existing vertical flux tubes which are parts of active regions or the remnants of active regions. These loops result from the kink (or helical) instability in a twisted flux tube. Their observed properties are explained in terms of the flux-rope theory of solar fields. The model is extended to some dynamical effects in emerging loops. Further observations of ephemeral active regions may provide important tests between the traditional and flux-rope theories of solar magnetic fields.

scholarly journals Flux Tubes and Dynamos

1993 ◽  
Vol 157 ◽  
pp. 27-39
Author(s):  
M. Schüssler
Keyword(s):  
Field Strength ◽  
Magnetic Flux ◽  
Convection Zone ◽  
Source Region ◽  
Mean Field ◽  
Active Regions ◽  
Dynamo Theory ◽  
Flux Tubes ◽  
Magnetic Structures ◽  
Magnetic Flux Tubes

The structure of solar surface magnetic fields, the way they erupt from the the convection zone below, and processes like flux expulsion and fragmentation instabilities support the view that magnetic flux in a stellar convection zone is in an intermittent, fragmented state which can be described as an ensemble of magnetic flux tubes. Depending on size and field strength, the dynamics of magnetic flux tubes can strongly differ from the behavior of a passive, diffuse field which is often assumed in conventional mean-field dynamo theory. Observed properties of active regions like emergence in low latitudes, Hale's polarity rules, tilt angles, and the process of sunspot formation from smaller fragments, together with theoretical considerations of the dynamics of buoyant flux tubes indicate that the magnetic structures which erupt in an emerging active region are not passive to convection and originate in a source region (presumably an overshoot layer below the convection zone proper) with a field strength of at least 105 G, far beyond the equipartition field strength with respect to convective flows. We discuss the consequences of such a situation for dynamo theory of the solar cycle and consider the possibility of dynamo models on the basis of flux tubes. A simple, illustrative example of a flux tube dynamo is presented.

scholarly journals Twist and writhe of δ-island active regions

2010 ◽  
Vol 6 (S273) ◽  
pp. 153-156
Author(s):  
M. C. López Fuentes ◽  
C. H. Mandrini ◽  
P. Démoulin
Keyword(s):  
Magnetic Field ◽  
Flux Tube ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Coronal Structure ◽  
Flux Tubes ◽  
Single Mechanism ◽  
Magnetic Flux Tubes ◽  
Kink Instability ◽  
The Magnetic Field

AbstractWe study the magnetic helicity properties of a set of peculiar active regions (ARs) including δ-islands and other high-tilt bipolar configurations. These ARs are usually identified as the most active in terms of flare and CME production. Due to their observed structure, they have been associated with the emergence of magnetic flux tubes that develop a kink instability. Our main goal is to determine the chirality of the twist and writhe components of the AR magnetic helicity in order to set constrains on the possible mechanisms producing the flux tube deformations. We determine the magnetic twist comparing observations of the AR coronal structure with force-free models of the magnetic field. We infer the flux-tube writhe from the rotation of the main magnetic bipole during the observed evolution. From the relation between the obtained twist and writhe signs we conclude that the development of the kink instability cannot be the single mechanism producing deformed flux-tubes.

scholarly journals Magnetic Helicity as a Predictor of the Solar Cycle

2017 ◽  
Vol 13 (S335) ◽  
pp. 20-22
Author(s):  
G. Hawkes ◽  
M. A. Berger
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Differential Rotation ◽  
Strong Predictor ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Poloidal Field ◽  
Northern And Southern Hemispheres

AbstractIt is known that the poloidal field is at its maximum during solar minima, and that the behaviour during this time acts as a strong predictor of the strength of the following solar cycle. This relationship relies on the action of differential rotation (the Omega effect) on the poloidal field, which generates the toroidal flux observed in sunspots and active regions. We measure the helicity flux into both the northern and southern hemispheres using a model that takes account of the omega effect, which we find offers a strong quantification of the above relationship. We find that said helicity flux offers a strong prediction of solar activity up to 5 years in advance of the next solar cycle.

scholarly journals The Suppression and Promotion of Magnetic Flux Emergence in Fully Convective Stars

2016 ◽  
Vol 12 (S328) ◽  
pp. 85-92
Author(s):  
Maria A. Weber ◽  
Matthew K. Browning ◽  
Suzannah Boardman ◽  
Joshua Clarke ◽  
Samuel Pugsley ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Differential Rotation ◽  
Flux Emergence ◽  
Surface Magnetism ◽  
Flux Tubes ◽  
Cool Stars ◽  
M Dwarf ◽  
Insight Into ◽  
Individual Flux

AbstractEvidence of surface magnetism is now observed on an increasing number of cool stars. The detailed manner by which dynamo-generated magnetic fields giving rise to starspots traverse the convection zone still remains unclear. Some insight into this flux emergence mechanism has been gained by assuming bundles of magnetic field can be represented by idealized thin flux tubes (TFTs). Weber & Browning (2016) have recently investigated how individual flux tubes might evolve in a 0.3M⊙ M dwarf by effectively embedding TFTs in time-dependent flows representative of a fully convective star. We expand upon this work by initiating flux tubes at various depths in the upper ~50-75% of the star in order to sample the differing convective flow pattern and differential rotation across this region. Specifically, we comment on the role of differential rotation and time-varying flows in both the suppression and promotion of the magnetic flux emergence process.

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