Torsional Oscillations of the Sun

1983 ◽  
Vol 66 ◽  
pp. 437-437
Author(s):  
Robert Howard
Keyword(s):  
Magnetic Flux ◽  
Shear Zone ◽  
Large Scale ◽  
Torsional Oscillation ◽  
Travelling Wave ◽  
Wave Number ◽  
The Sun ◽  
High Latitudes ◽  
Dynamo Action ◽  
Average Rotation

AbstractA series of digitized synoptic observations of solar magnetic and velocity fields has been carried out at the Mount Wilson Observatory since 1967. In recent studies (Howard and LaBonte, 1980; LaBonte and Howard, 1981), the existence of slow, large-scale torsional (toroidal) oscillations of the Sun has been demonstrated. Two modes have been identified. The first is a travelling wave, symmetric about the equator, with wave number 2 per hemisphere. The pattern-alternately slower and faster than the average rotation–starts at the poles and drifts to the equator in an interval of 22 years. At any one latitude on the Sun, the period of the oscillation is 11 years, and the amplitude is 3 m s-1. The magnetic flux emergence that is seen as the solar cycle occurs on average at the latitude of one shear zone of this oscillation. The amplitude of the shear is quite constant from the polar latitudes to the equator. The other mode of torsional oscillation, superposed on the first mode, is a wave number 1 per hemisphere pattern consisting of faster than average rotation at high latitudes around solar maximum and faster than average rotation at low latitudes near solar minimum. The amplitude of the effect is about 5 m s1-. For the first mode, the close relationship in latitude between the activity-related magnetic flux eruption and the torsional shear zone suggests strongly that there is a close connection between these motions and the cycle mechanism. It has been suggested (Yoshimura, 1981; Schüssler, 1981) that the effect is caused by a subsurface Lorentz force wave resulting from the dynamo action of magnetic flux ropes. But, this seems unlikely because of the high latitudes at which the shear wave is seen to originate and the constancy of the magnitude of the shear throughout the life time of the wave.

scholarly journals Nonlinear evolution of the parametric instability: numerical predictions versus observations in the heliosphere

2001 ◽  
Vol 8 (3) ◽  
pp. 159-166 ◽  
Author(s):  
F. Malara ◽  
L. Primavera ◽  
P. Veltri
Keyword(s):  
Large Scale ◽  
Parametric Instability ◽  
Low Frequency ◽  
Heliospheric Current Sheet ◽  
Mhd Equations ◽  
Alfven Wave ◽  
The Sun ◽  
High Latitudes ◽  
Initial Correlation ◽  
Numerical Predictions

Abstract. Low-frequency turbulence in the solar wind is characterized by a high degree of Alfvénicity close to the Sun. Cross-helicity, which is a measure of Alfvénic correlation, tends to decrease with increasing distance from the Sun at high latitudes as well as in slow-speed streams at low latitudes. In the latter case, large scale inhomogeneities (velocity shears, the heliospheric current sheet) are present, which are sources of decorrelation; yet at high latitudes, the wind is much more homogeneous, and a possible evolution mechanism is represented by the parametric instability. The parametric decay of an circularly polarized broadband Alfvén wave is then investigated, as a source of decorrelation. The time evolution is followed by numerically integrating the full set of nonlinear MHD equations, up to instability saturation. We find that, for <beta>  ~ 1, the final cross-helicity is ~ 0.5, corresponding to a partial depletion of the initial correlation. Compressive fluctuations at a moderate level are also present. Most of the spectrum is dominated by forward propagating Alfvénic fluctuations, while backscattered fluctuations dominate large scales. With increasing time, the spectra of Elsässer variables tend to approach each other. Some results concerning quantities measured in the high-latitude wind are reviewed, and a qualitative agreement with the results of the numerical model is found.

scholarly journals On the peculiarities of manifestation of kG magnetic elements in observations of the Sun with low spatial resolution

2014 ◽  
Vol 10 (S305) ◽  
pp. 86-91 ◽  
Author(s):  
Mikhail L. Demidov ◽  
Renat M. Veretsky ◽  
Alexander V. Kiselev
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Spatial Resolution ◽  
Large Scale ◽  
Disk Center ◽  
Stellar Disk ◽  
The Sun ◽  
Surface Mapping ◽  
Cross Calibration ◽  
Stellar Magnetic Fields

AbstractOn the agenda of modern astrophysics is the exploration of not only disk-integrated stellar magnetic fields but surface mapping of them. However, it is hardly possible to expect that spatial resolution better than some dozens or hundreds pixels over stellar disk will be achieved for this goal in the foreseeable future. Among other reasons this fact makes very important observations of the average and large-scale magnetic fields of the Sun, which can be naturally used for testing polarimetric measurements on other stars, especially on solar-type stars. In this study we explore different aspects of observations of solar magnetic fields (SMF) with low spatial resolution, including Sun-as-a-star observations, which are characterized by extremely low magnetic flux densities. Comparison of disk-integrated and spatially resolved Stokes observations of the Sun allow us to demonstrate how Stokes V profiles depend on the distribution of large-scale magnetic fields in the disk center. It is shown that center-to-limb variations of magnetic strength ratios (MSR) and area asymetries, most likely could be interpreted as the manifestation of kG magnetic flux tubes. We have made cross-calibration of the full-disk magnetograms obtained by space-borned SDO/HMI and by the ground-based STOP telescope, and pretty good agreement is found. Finally, the absence of significant systematic time variations of MSRs with solar cycle is demonstrated.

Solar Dynamo

2020 ◽  
Author(s):  
Robert Cameron
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Differential Rotation ◽  
Large Scale ◽  
Toroidal Field ◽  
Solar Dynamo ◽  
Small Scale ◽  
The Sun ◽  
The Magnetic Field

The solar dynamo is the action of flows inside the Sun to maintain its magnetic field against Ohmic decay. On small scales the magnetic field is seen at the solar surface as a ubiquitous “salt-and-pepper” disorganized field that may be generated directly by the turbulent convection. On large scales, the magnetic field is remarkably organized, with an 11-year activity cycle. During each cycle the field emerging in each hemisphere has a specific East–West alignment (known as Hale’s law) that alternates from cycle to cycle, and a statistical tendency for a North-South alignment (Joy’s law). The polar fields reverse sign during the period of maximum activity of each cycle. The relevant flows for the large-scale dynamo are those of convection, the bulk rotation of the Sun, and motions driven by magnetic fields, as well as flows produced by the interaction of these. Particularly important are the Sun’s large-scale differential rotation (for example, the equator rotates faster than the poles), and small-scale helical motions resulting from the Coriolis force acting on convective motions or on the motions associated with buoyantly rising magnetic flux. These two types of motions result in a magnetic cycle. In one phase of the cycle, differential rotation winds up a poloidal magnetic field to produce a toroidal field. Subsequently, helical motions are thought to bend the toroidal field to create new poloidal magnetic flux that reverses and replaces the poloidal field that was present at the start of the cycle. It is now clear that both small- and large-scale dynamo action are in principle possible, and the challenge is to understand which combination of flows and driving mechanisms are responsible for the time-dependent magnetic fields seen on the Sun.

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’.

Coronal Large-Scale Structure in Odd and Even 11-Year Cycles

1994 ◽  
Vol 144 ◽  
pp. 96
Author(s):  
V. I. Makarov ◽  
V. P. Mikhailutsa ◽  
M. P. Fatianov ◽  
T. V. Stepanova
Keyword(s):  
Large Scale ◽  
Radial Direction ◽  
Solar Magnetic Field ◽  
Essential Difference ◽  
The Sun ◽  
High Latitudes ◽  
Solar Cycles ◽  
Magnetic Cycle ◽  
Solar Magnetic Cycle ◽  
Odd Cycles

AbstractObservations of 22 solar eclipses (1914-1991) have been processed. Radial deviations of streamers in the polar and equatorial zones of the Sun in odd and even solar cycles have been studied. An essential difference of the degree of non-radiality of coronal rays at the same latitudes in odd and even cycles has been found. Deviations from the radial direction of streamers are large in the polar zones in the epoch of the maxima of even cycles and in the equatorial zones at the minima of odd cycles. Deviations from radiality at high latitudes are observed mainly in the poleward direction. The results obtained are interpreted in terms of a new model of the cycle, in which the properties of the solar magnetic field depend on the phase of a 22-year solar magnetic cycle.

scholarly journals HMI observations of two types of ephemeral regions

2013 ◽  
Vol 8 (S300) ◽  
pp. 470-472
Author(s):  
Shuhong Yang ◽  
Jun Zhang ◽  
Yang Liu
Keyword(s):  
Magnetic Flux ◽  
Large Scale ◽  
Active Regions ◽  
The Self ◽  
The Sun ◽  
Number Density ◽  
Flux Loops ◽  
Background Fields

AbstractUsing the magnetograms observed with the Helioseismic and Magnetic Imager, we statistically study the ephemeral regions (ERs) of the Sun. we notice that the areas with locations around S15° and N25° have larger ER number density, implying that the generation of ERs may be affected by the large-scale background fields from dispersed active regions. According to their evolution, the ERs can be classified into two types, i.e., normal ERs (2798 ones) and self-canceled ERs (190 ones). Submergence of initial magnetic flux loops connecting the opposite dipolar polarities may lead to the self-cancellation.

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 Flux Separation in Photospheric Magnetoconvection

2001 ◽  
Vol 203 ◽  
pp. 219-221 ◽  
Author(s):  
N. O. Weiss ◽  
M. R. E. Proctor
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Numerical Experiments ◽  
Large Scale ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Small Scale ◽  
The Sun ◽  
Intermediate Regime ◽  
Magnetic Features

Numerical experiments on three-dimensional magnetoconvection in a stratified compressible layer reveal a range of different patterns, depending on the strength of the imposed magnetic field. As the field is decreased there is a transition from small-scale plumes, in the magnetically dominated regime, to large-scale vigorous plumes when the field is dominated by the motion. In the intermediate regime magnetic flux separates from the motion, so that there are almost field-free regions, with clusters of vigorous plumes, surrounded by regions where the Lorentz force is strong enough to control the dynamics. There is a range of field strengths where either small-scale plumes or flux-separated solutions can persist, depending on initial conditions for the computation. These results can be related to magnetic features at the surface of the Sun.

Large-scale transport of solar and stellar magnetic flux

2018 ◽  
Vol 14 (A30) ◽  
pp. 347-350
Author(s):  
Emre Işık
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Large Scale ◽  
Surface Flux ◽  
Current Understanding ◽  
Solar Photosphere ◽  
The Sun ◽  
Forward Modelling ◽  
Flux Transport ◽  
Brightness Variability

AbstractSurface flux transport (SFT) models have been successful in reproducing how magnetic flux at the solar photosphere evolves on large scales. SFT modelling proved to be useful in reconstructing secular irradiance variations of the Sun, and it can be potentially used in forward modelling of brightness variations of Sun-like stars. We outline our current understanding of solar and stellar SFT processes, and suggest that nesting of activity can play an important role in shaping large-scale patterns of magnetic fields and brightness variability.

scholarly journals Modelling Stellar Magnetoconvection

2003 ◽  
Vol 210 ◽  
pp. 127-142 ◽  
Author(s):  
N. O. Weiss
Keyword(s):  
Numerical Experiments ◽  
Large Scale ◽  
Small Scale ◽  
The Sun ◽  
Late Type ◽  
Dynamo Action ◽  
Magnetic Features ◽  
Flux Expulsion

This review focuses on different patterns of magnetoconvection and on aspects of flux expulsion, flux separation and flux pumping. The transition between magnetoconvection and small-scale dynamo action will be described and the rôle of rotation in leading to large-scale dynamo action will be emphasized. An attempt will be made to relate the results of numerical experiments to magnetic features that can be observed on the Sun, and must also be present in other late-type stars.

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