scholarly journals Flux Emergence and the Evolution of Large-Scale Photospheric Field Patterns

1993 ◽  
Vol 141 ◽  
pp. 487-487
Author(s):  
Y.-M. Wang ◽  
N. R. Sheeley
Keyword(s):  
Large Scale ◽  
Transport Model ◽  
Solar Surface ◽  
Rotation Period ◽  
Active Regions ◽  
Meridional Flow ◽  
Flux Transport ◽  
Field Patterns ◽  
Complete Discussion ◽  
Qualitative Nature

AbstractStackplot displays of the photospheric magnetic field show long-lived patterns that often rotate at rates differing from the intrinsic photospheric rate. These complex patterns are produced naturally by the flux-transport model, in which magnetic flux emerging in the form of active regions is dispersed over the solar surface by differential rotation, supergranular diffusion, and a poleward meridional flow. Numerical simulations show that long-lived patterns with slopes similar to the observed ones arise even when the longitudes of the erupting flux are randomized, suggesting that a deep-seated longitudinal organization is not required to explain the qualitative nature of the patterns. Both autocorrelation analysis and visual comparison between the slopes of the observed and simulated patterns indicate that the equatorial rotation period of the Sun is close to 26.75 days, significantly shorter than the traditional 26.9 day value of Snodgrass and Newton & Nunn but in agreement with the recent measurements of Komm, Howard, & Harvey. A complete discussion of these results may be found in Sheeley, Wang, & Nash, ApJ, 401, 378 (1992).

scholarly journals The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations

2018 ◽  
Vol 853 (1) ◽  
pp. 72 ◽  
Author(s):  
Dibyendu Nandy ◽  
Prantika Bhowmik ◽  
Anthony R. Yeates ◽  
Suman Panda ◽  
Rajashik Tarafder ◽  
...  
Keyword(s):  
Large Scale ◽  
Transport Model ◽  
Solar Surface ◽  
Surface Flux ◽  
Coronal Structure ◽  
Flux Transport

scholarly journals Rotation of Large Scale Patterns on the Solar Surface as Determined from Filament and Millimeter Data

1991 ◽  
Vol 130 ◽  
pp. 279-281
Author(s):  
S. Pohjolainen ◽  
B. Vršnak ◽  
H. Teräsranta ◽  
S. Urpo ◽  
R. Brajša ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Low Temperature ◽  
Large Scale ◽  
Solar Magnetic Field ◽  
Solar Surface ◽  
Field Patterns

AbstractThe rotation of large scale solar magnetic field patterns was studied using quiescent filaments and low temperature regions observed at 37 GHz as tracers.

scholarly journals How Good Is the Bipolar Approximation of Active Regions for Surface Flux Transport?

Solar Physics ◽  
2020 ◽  
Vol 295 (9) ◽  
Author(s):  
Anthony R. Yeates
Keyword(s):  
Dipole Moment ◽  
Active Region ◽  
Transport Model ◽  
Active Regions ◽  
Surface Flux ◽  
Flux Transport ◽  
Transport Models ◽  
Magnetic Structures ◽  
Axial Dipole ◽  
Flow Parameters

Abstract We investigate how representing active regions with bipolar magnetic regions (BMRs) affects the end-of-cycle polar field predicted by the surface flux transport model. Our study is based on a new database of BMRs derived from the SDO/HMI active region patch data between 2010 and 2020. An automated code is developed for fitting each active region patch with a BMR, matching both the magnetic flux and axial dipole moment of the region and removing repeat observations of the same region. By comparing the predicted evolution of each of the 1090 BMRs with the predicted evolution of their original active region patches, we show that the bipolar approximation leads to a 24% overestimate of the net axial dipole moment, given the same flow parameters. This is caused by neglecting the more complex multipolar and/or asymmetric magnetic structures of many of the real active regions, and may explain why previous flux transport models had to reduce BMR tilt angles to obtain realistic polar fields. Our BMR database and the Python code to extract it are freely available.

scholarly journals Two classes of eruptive events during Solar Minimum

2021 ◽  
Author(s):  
Prantika Bhowmik ◽  
Anthony Yeates
Keyword(s):  
Magnetic Field ◽  
Free Energy ◽  
Magnetic Flux ◽  
Solar Minimum ◽  
Large Scale ◽  
Solar Surface ◽  
Coronal Holes ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
The Magnetic Field

<p>During Solar Minimum, the Sun is perceived to be quite inactive with barely any spots emerging on the solar surface. Consequently, we observe a drop in the number of highly energetic events such as solar flares and coronal mass ejections (CMEs), which are often associated with active regions on the photosphere. However, our magnetofrictional simulations during the minimum period suggest that the solar corona could still be significantly dynamic while evolving in response to the large-scale shearing velocities on the solar surface. The non-potential evolution of the corona leads to the accumulation of magnetic free energy and helicity, which is periodically lost through eruptive events. Our study shows that these events can be categorised into two distinct classes. One set of events are caused due to full-scale eruption of low-lying coronal flux ropes and could be associated with occasional filament erupting CMEs observed during Solar Minimum. The other set of events are not driven by destabilisation of low-lying structures but rather by eruption from overlying sheared arcades. These could be linked with streamer blowouts or stealth CMEs. The two classes differ considerably in the amount of magnetic flux and helicity shed through the outer coronal boundary. We additionally investigate how other measurables such as current, open magnetic flux, free energy, coronal holes area, and the horizontal component of the magnetic field on the outer model boundary vary during the two classes of event. This study demonstrates and emphasises the importance and necessity of understanding the dynamics of the coronal magnetic field during Solar Minimum.</p>

scholarly journals Numerical Simulations of Large-scale Solar Magnetic Fields

1985 ◽  
Vol 38 (6) ◽  
pp. 999 ◽  
Author(s):  
CR DeVore ◽  
NR Sheeley Jr ◽  
JP Boris ◽  
TR Young Jr ◽  
KL Harvey
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Large Scale ◽  
Sunspot Cycle ◽  
Active Regions ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Field Patterns ◽  
Large Scale Magnetic Field ◽  
The Magnetic Field

We have solved numerically a transport equation which describes the evolution of the large-scale magnetic field of the Sun. Data derived from solar magnetic observations are used to initialize the computations and to account for the emergence of new magnetic flux during the sunspot cycle. Our objective is to assess the ability of the model to reproduce the observed evolution of the field patterns. We discuss recent results from simulations of individual active regions over a few solar rotations and of the magnetic field of the Sun over sunspot cycle 21.

scholarly journals Observations of the Solar Corona from Space

2020 ◽  
Vol 216 (8) ◽  
Author(s):  
Ester Antonucci ◽  
Louise Harra ◽  
Roberto Susino ◽  
Daniele Telloni
Keyword(s):  
Solar Cycle ◽  
Solar Corona ◽  
Large Scale ◽  
Coronal Holes ◽  
Active Regions ◽  
Coronal Emission ◽  
Field Patterns ◽  
Magnetic Cycles ◽  
Outer Corona

AbstractSpace observations of the atmosphere of the Sun, obtained in half a century of dedicated space missions, provide a well established picture of the medium and large-scale solar corona, which is highly variable with the level of solar activity through a solar cycle and evolves with the long-term evolution of the magnetic cycles. In this review, we summarize the physical properties and dynamics of the medium and large-scale corona, consisting primarily of active regions, streamers and coronal holes; describe the dependence of coronal patterns on the magnetic field patterns changing through the solar cycle and the properties of the regions of open magnetic flux channeling the solar wind; the ubiquitous presence of fluctuations in the outer corona; the rotational properties of the large-scale corona; and the persistent hemispheric asymmetries in the emergence of magnetic fields and the distribution of the coronal emission.

scholarly journals Magnetohydrodynamic Simulation of the Evolution of Bipolar Magnetic Regions

1993 ◽  
Vol 141 ◽  
pp. 98-107 ◽  
Author(s):  
S. T. Wu ◽  
C. L. Yin ◽  
P. Mcintosh ◽  
E. Hildner
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Differential Rotation ◽  
Solar Surface ◽  
Effective Diffusion ◽  
Three Dimensional ◽  
Meridional Flow ◽  
Flux Transport ◽  
Turbulence Effects ◽  
Convective Motions

AbstractIt has been recognized that the magnetic flux observed on the solar surface appears first in low latitudes, and then this flux is gradually dispersed by super granular convective motions and meridional circulation. Theoretically, the magnetic flux transport could be explained by the interactions between magnetic fields and plasma flows on the solar surface through the theory of magnetohydrodynamics.To understand this physical scenario, a quasi-three-dimensional, time-dependent, MHD model with differential rotation, meridional flow and effective diffusion as well as cyclonic turbulence effects is developed. Numerical experiments are presented for the study of Bipolar Magnetic Regions (BMRs). When the MHD effects are ignored, our model produced the classical results (Leighton, Astrophys. J., 146, 1547, 1964). The full model’s numerical results demonstrate that the interaction between magnetic fields and plasma flow (i.e., MHD effects), observed together with differential rotation and meridional flow, gives rise to the observed complexity of the evolution of BMRs.

scholarly journals Helioseismic inferences on subsurface solar convection

2006 ◽  
Vol 2 (S239) ◽  
pp. 113-121
Author(s):  
Alexander G. Kosovichev
Keyword(s):  
Large Scale ◽  
Meridional Flow ◽  
Polar Regions ◽  
Flux Transport ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
New Methods ◽  
Global Properties ◽  
The Mean ◽  
Depth Stratification

AbstractHelioseismology has provided robust estimates of global properties of the solar convection zone, its depth, stratification, and revealed rotational shear layers at the boundaries. New methods of local helioseismology provide 3D maps of subsurface convective flows. In the quiet Sun regions, these maps reveal that supergranular-scale convection extends to the depth of 12–15 Mm. Analysis of evolution of the supergranular convection pattern shows evidence for a wave-like behavior which might be related to the interaction between convection and the subsurface rotational sheer layer. Helioseismology also reveals large-scale circulation flows around magnetic regions. These flows affect the evolution of the mean meridional flow during the solar cycle and, probably, the magnetic flux transport from mid-latitudes to the polar regions, a process important for solar dynamo theories. Helioseismic measurements on a smaller scale, below sunspots, give insight on how convection interacts with strong magnetic fields.

scholarly journals Time Variations of Solar X-ray Bright Points

1975 ◽  
Vol 68 ◽  
pp. 23-24
Author(s):  
L. Golub ◽  
A. S. Krieger ◽  
J. K. Silk ◽  
A. F. Timothy ◽  
G. S. Vaiana
Keyword(s):  
Large Scale ◽  
Solar Surface ◽  
Active Regions ◽  
Lifetime Distribution ◽  
Comprehensive Review ◽  
X Ray ◽  
High Loop ◽  
Diffuse Cloud ◽  
Time Variations ◽  
Present Summary

SummaryAn example of the overall view of the X-ray corona (nominal filter passband 2–32 Å and 44–54 Å) showing a coronal hole, filament activity, bright points and the large scale-scale loop structures, is shown in Figure 1. This is one of the 32000 X-ray images obtained with the AS & E X-ray telescope on Skylab. A comprehensive review describing the characteristics of the various features and their implications regarding the high velocity solar streams, evolution of magnetic fields in active regions, and sources of soft X-ray emission has been given by Vaiana et al. (1975). In the present summary we will only be concerned with the bright points. Studies of solar X-ray bright points, show that these features represent a distinct class of solar activity. Bright points appear first as a diffuse cloud of soft X-ray emission typically growing to 30″ in diameter, with growth rates of ∼1 km s−1. Several hours after the point first becomes visible a bright compact core forms, growing to 10″. The lifetime distribution of bright points follows a Poisson distribution with a mean of eight hours (see references). The points are distributed uniformly over the entire solar surface, with approximately 500 on the Sun at any time. Their occurrrence appears to be independent of major active regions, except for a visibility factor near high loop structures or a possible decrease in number in active region latitudes.

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