Evolutionary Characteristics of Large-Scale Magnetic and Velocity Fields

1993 ◽  
Vol 141 ◽  
pp. 495-499
Author(s):  
Pavel Ambrož
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Flux Distribution ◽  
Active Regions ◽  
Giant Cells ◽  
Velocity Fields ◽  
Magnetized Plasma ◽  
Horizontal Flow ◽  
Term Evolution

AbstractLong-term evolution of solar large-scale magnetic fields in relation to the local active phenomena is studied. The changes of the magnetic flux distribution are influenced by the horizontal transport of magnetized plasma. The whole system of magnetic field changes is interpreted as a global process which is controlled by the large-scale convective patterns. The large-scale horizontal velocity field of transporting motions is determined in various approaches with similar results. Regions with positive divergence in the field of horizontal flow field are found to be closely connected with the occurrence of solar active regions. The process of the horizontal flow was analysed by the “cork” method. The corks reveal a pattern of giant cells which are persistent for several solar rotations. These large cells are interpreted as giant convective elements. Occurrence of new strong magnetic flux in regions of positive divergence is then interpreted as a result of emergence of flux in the upflowing parts of that pattern.

scholarly journals Reconstructing solar magnetic fields from historical observations

2019 ◽  
Vol 627 ◽  
pp. A11
Author(s):  
I. O. I. Virtanen ◽  
I. I. Virtanen ◽  
A. A. Pevtsov ◽  
L. Bertello ◽  
A. Yeates ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Active Regions ◽  
Long Term Evolution ◽  
Photospheric Magnetic Field ◽  
Solar Magnetic Fields ◽  
Term Evolution ◽  
Large Scale Field

Aims. The evolution of the photospheric magnetic field has only been regularly observed since the 1970s. The absence of earlier observations severely limits our ability to understand the long-term evolution of solar magnetic fields, especially the polar fields that are important drivers of space weather. Here, we test the possibility to reconstruct the large-scale solar magnetic fields from Ca II K line observations and sunspot magnetic field observations, and to create synoptic maps of the photospheric magnetic field for times before modern-time magnetographic observations. Methods. We reconstructed active regions from Ca II K line synoptic maps and assigned them magnetic polarities using sunspot magnetic field observations. We used the reconstructed active regions as input in a surface flux transport simulation to produce synoptic maps of the photospheric magnetic field. We compared the simulated field with the observed field in 1975−1985 in order to test and validate our method. Results. The reconstruction very accurately reproduces the long-term evolution of the large-scale field, including the poleward flux surges and the strength of polar fields. The reconstruction has slightly less emerging flux because a few weak active regions are missing, but it includes the large active regions that are the most important for the large-scale evolution of the field. Although our reconstruction method is very robust, individual reconstructed active regions may be slightly inaccurate in terms of area, total flux, or polarity, which leads to some uncertainty in the simulation. However, due to the randomness of these inaccuracies and the lack of long-term memory in the simulation, these problems do not significantly affect the long-term evolution of the large-scale field.

scholarly journals Large scale magnetic helicity fluxes estimated from MDI magnetic synoptic charts

2012 ◽  
Vol 8 (S294) ◽  
pp. 157-158
Author(s):  
Shangbin Yang ◽  
Hongqi Zhang
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Solar Disk ◽  
Large Scale ◽  
Magnetic Helicity ◽  
Local Correlation ◽  
Solar Cycles ◽  
23Rd Solar Cycle ◽  
Term Evolution

AbstractTo investigate the characteristics of large scale and long term evolution of magnetic helicity with solar cycles, we use the method of Local Correlation Tracking (LCT) to estimate the magnetic helicity evolution over the 23rd solar cycle from 1996 to 2009 by using 795 MDI magnetic synoptic charts. The main results are: the hemispheric helicity rule still holds in general, i.e. the large-scale negative (positive) magnetic helicity dominates the northern (southern) hemisphere. However, the large scale magnetic helicity fluxes show the same sign in both hemispheres around 2001 and 2005. The global, large scale magnetic helicity flux over the solar disk changes from negative value at the beginning of the 23rd solar cycle to positive value at the end of the cycle, which also shows the similar trend from the normalized magnetic flux by using the magnetic flux. The net accumulated magnetic helicity is negative in the period between 1996 and 2009.

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

scholarly journals A statistical study of the long-term evolution of coronal hole properties as observed by SDO

2020 ◽  
Vol 638 ◽  
pp. A68 ◽  
Author(s):  
S. G. Heinemann ◽  
V. Jerčić ◽  
M. Temmer ◽  
S. J. Hofmeister ◽  
M. Dumbović ◽  
...  
Keyword(s):  
Solar Wind ◽  
Magnetic Flux ◽  
Coronal Hole ◽  
High Speed ◽  
Coronal Holes ◽  
Magnetic Flux Density ◽  
High Speed Stream ◽  
Term Evolution ◽  
Hole Area

Context. Understanding the evolution of coronal holes is especially important when studying the high-speed solar wind streams that emanate from them. Slow- and high-speed stream interaction regions may deliver large amounts of energy into the Earth’s magnetosphere-ionosphere system, cause geomagnetic storms, and shape interplanetary space. Aims. By statistically investigating the long-term evolution of well-observed coronal holes we aim to reveal processes that drive the observed changes in the coronal hole parameters. By analyzing 16 long-living coronal holes observed by the Solar Dynamic Observatory, we focus on coronal, morphological, and underlying photospheric magnetic field characteristics, and investigate the evolution of the associated high-speed streams. Methods. We use the Collection of Analysis Tools for Coronal Holes to extract and analyze coronal holes using 193 Å EUV observations taken by the Atmospheric Imaging Assembly as well as line–of–sight magnetograms observed by the Helioseismic and Magnetic Imager. We derive changes in the coronal hole properties and look for correlations with coronal hole evolution. Further, we analyze the properties of the high–speed stream signatures near 1AU from OMNI data by manually extracting the peak bulk velocity of the solar wind plasma. Results. We find that the area evolution of coronal holes shows a general trend of growing to a maximum followed by a decay. We did not find any correlation between the area evolution and the evolution of the signed magnetic flux or signed magnetic flux density enclosed in the projected coronal hole area. From this we conclude that the magnetic flux within the extracted coronal hole boundaries is not the main cause for its area evolution. We derive coronal hole area change rates (growth and decay) of (14.2 ± 15.0)×108 km2 per day showing a reasonable anti-correlation (ccPearson = −0.48) to the solar activity, approximated by the sunspot number. The change rates of the signed mean magnetic flux density (27.3 ± 32.2 mG day−1) and the signed magnetic flux (30.3 ± 31.5 1018 Mx day−1) were also found to be dependent on solar activity (ccPearson = 0.50 and ccPearson = 0.69 respectively) rather than on the individual coronal hole evolutions. Further we find that the relation between coronal hole area and high-speed stream peak velocity is valid for each coronal hole over its evolution, but we see significant variations in the slopes of the regression lines.

scholarly journals Effect of Turbulence on Emerging Magnetic Flux Tubes in the Convection Zone

1990 ◽  
Vol 142 ◽  
pp. 60-61
Author(s):  
Sydney D'Silva ◽  
Arnab Rai Choudhuri
Keyword(s):  
Magnetic Flux ◽  
Coriolis Force ◽  
Large Scale ◽  
Convection Zone ◽  
Rotation Axis ◽  
Giant Cells ◽  
Magnetic Flux Tube ◽  
Small Scale ◽  
Flux Tubes ◽  
Scale Turbulence

Working under the hypothesis that magnetic flux in the sun is generated at the bottom of the convection zone, Choudhuri and Gilman (1987; Astrophys. J. 316, 788) found that a magnetic flux tube symmetric around the rotation axis, when released at the bottom of the convection zone, gets deflected by the Coriolis force and tends to move parallel to the rotation axis as it rises in the convection zone. As a result, all the flux emerges at rather high latitudes and the flux observed at the typical sunspot latitudes remains unexplained. Choudhuri(1989; Solar Physics, in press) finds that non-axisymmetric perturbations too cannot subdue the Coriolis force. In this paper, we no longer treat the convection zone to be passive as in the previous papers, but we consider the role of turbulence in the convection zone in inhibiting the Coriolis force. The interaction of the flux tubes with the turbulence is treated in a phenomenological way as follows: (1) Large scale turbulence on the scale of giant cells can physically drag the tubes outwards, thus pulling the flux towards lower latitudes by dominating over the Coriolis force. (2) Small scale turbulence of the size of the tubes can exchange angular momentum with the tube, thus suppressing the growth of the Coriolis force and making the tubes emerge at lower latitudes. Numerical simulations show that the giant cells can drag the tubes and make them emerge at lower latitudes only if the velocities within the giant cells are unrealistically large or if the radii of the flux tubes are as small as 10 km. However, small scale turbulence can successfully suppress the growth of the Coriolis force if the tubes have radii smaller than about 300 km which may not be unreasonable. Such flux tubes can then emerge at low latitudes where sunspots are seen.

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 The emergence of magnetic flux and its role on the onset of solar dynamic events

2019 ◽  
Vol 377 (2148) ◽  
pp. 20180387 ◽  
Author(s):  
V. Archontis ◽  
P. Syntelis
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Spatial Scales ◽  
Active Regions ◽  
Short Review ◽  
The Sun ◽  
Flux Emergence ◽  
Dynamic Events ◽  
Solar Eruptions ◽  
Solar Dynamics

A plethora of solar dynamic events, such as the formation of active regions, the emission of jets and the occurrence of eruptions is often associated with the emergence of magnetic flux from the interior of the Sun to the surface and above. Here, we present a short review on the onset, driving and/or triggering of such events by magnetic flux emergence. We briefly describe some key observational examples, theoretical aspects and numerical simulations, towards revealing the mechanisms that govern solar dynamics and activity related to flux emergence. We show that the combination of important physical processes like shearing and reconnection of magnetic fieldlines in emerging flux regions or at their vicinity can power some of the most dynamic phenomena in the Sun on various temporal and spatial scales. Based on previous and recent observational and numerical studies, we highlight that, in most cases, none of these processes alone can drive and also trigger explosive phenomena releasing considerable amount of energy towards the outer solar atmosphere and space, such as flares, jets and large-scale eruptions (e.g. coronal mass ejections). In addition, one has to take into account the physical properties of the emerging field (e.g. strength, amount of flux, relative orientation to neighbouring and pre-existing magnetic fields, etc.) in order to better understand the exact role of magnetic flux emergence on the onset of solar dynamic events. This article is part of the theme issue ‘Solar eruptions and their space weather impact’.

Hydrogeological simulation of sedimentary basin evolution during a glacial cycle

2021 ◽  
Author(s):  
Christian Silbermann
Keyword(s):  
Boundary Conditions ◽  
Large Scale ◽  
Sedimentary Basin ◽  
Long Term Evolution ◽  
Nuclear Waste Repository ◽  
Glacial Cycle ◽  
Thermal Problem ◽  
Term Evolution ◽  
The Impact

<p><strong>Co-authors: Francesco Parisio, Thomas Nagel</strong></p><p>Glaciation cycles affect the long-term evolution of geosystems by crustal deformation, ground freezing and thawing, as well as large-scale hydrogeological changes. In order to properly understand the present and future conditions of potential nuclear waste repository sites, we need to simulate the past history. <br>For this, a sedimentary basin is considered here as a large-scale hydrogeological benchmark study. The long-term evolution during one glacial cycle is simulated using the open-source multi-field finite element code <em>OpenGeoSys</em>. The impact of the glacial loading (weight and induced shear) is taken into account using appropriate time-dependent stress boundary conditions. As a preliminary study, the hydro-mechanically coupled problem and the thermal problem are considered separately. For comparison with a previously published study by Bense et al. (2008), the entire displacement field is prescribed and the groundwater evolution (hydraulic problem) is regarded. Then, the displacement is only prescribed by means of boundary conditions. The impact of different constitutive assumptions on the deformation and hydraulic behavior is analyzed. The thermal problem is used to simulate the evolution of frost bodies in the subsurface beneath and ahead of the glacier.</p><p>V. F. Bense and M. A. Person. Transient hydrodynamics within intercratonic sedimentary basins during glacial cycles. Journal of Geophysical Research,<br>113(F4):F04005, 10 2008.</p>

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