Identification of linear slow sausage waves in magnetic pores

AbstractThe analysis of an 11-hour series of high resolution white light observations of a large pore in the sunspot group NOAA 7519, observed on 5 June 1993 with the Swedish Vacuum Solar Telescope at La Palma on Canary Islands, has been recently described by Dorotovičet al. (2002). Special attention was paid to the evolution of a filamentary region attached to the pore, to horizontal motions around the pore, and to small-scale morphological changes. One of the results, relevant to out work here, was the determination of temporal area evolution of the studied pore where the area itself showed a linear trend of decrease with time at an average rate of −0.23 Mm2h−1during the entire observing period. Analysing the time series of the are of the pore, there is strong evidence that coupling between the solar interior and magnetic atmosphere can occur at various scales and that the referred decrease of the area may be connected with a decrease of the magnetic field strength according to the magnetic field-to-size relation. Periods of global acoustic, e.g.p-mode, driven waves are usually in the range of 5–10 minutes, and are favourite candidates for the coupling of interior oscillations with atmospheric dynamics. However, by assuming that magneto-acoustic gravity waves may be there too, and may act as drivers, the observed periodicities (frequencies) are expected to be much longer (smaller), falling well within the mMHz domain. In this work we determine typical periods of such range in the area evolution of the pore using wavelet analysis. The resulted periods are in the range of 20–70 minutes, suggesting that periodic elements of the temporal evolution of the area of this studied pore could be linked to, and considered as, observational evidence of linear low-frequency slow sausage (magneto-acoustic gravity) waves in magnetic pores. This would give us further evidence on the coupling of global solar oscillations to the overlaying magnetic atmosphere.

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Numerical models of sunspot formation and fine structure

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2011.0556 ◽

2012 ◽

Vol 370 (1970) ◽

pp. 3114-3128 ◽

Cited By ~ 3

Author(s):

Matthias Rempel

Keyword(s):

Magnetic Field ◽

Fine Structure ◽

Large Scale ◽

Numerical Models ◽

Dynamical Evolution ◽

Solar Interior ◽

Small Scale ◽

Wide Range ◽

Umbral Dots ◽

The Magnetic Field

Sunspots are central to our understanding of solar (and stellar) magnetism in many respects. On the large scale, they link the magnetic field observable in the photosphere to the dynamo processes operating in the solar interior. Properly interpreting the constraints that sunspots impose on the dynamo process requires a detailed understanding of the processes involved in their formation, dynamical evolution and decay. On the small scale, they give an insight into how convective energy transport interacts with the magnetic field over a wide range of field strengths and inclination angles, leading to sunspot fine structure observed in the form of umbral dots and penumbral filaments. Over the past decade, substantial progress has been made on both observational and theoretical sides. Advanced ground- and space-based observations have resolved, for the first time, the details of umbral dots and penumbral filaments and discovered similarities in their substructures. Numerical models have advanced to the degree that simulations of entire sunspots with sufficient resolution to resolve sunspot fine structure are feasible. A combination of improved helioseismic inversion techniques with seismic forward modelling provides new views on the subsurface structure of sunspots. In this review, we summarize recent progress, with particular focus on numerical modelling.

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Long-period variations in the magnetic field of small-scale solar structures

Geomagnetism and Aeronomy ◽

10.1134/s0016793216080211 ◽

2016 ◽

Vol 56 (8) ◽

pp. 1052-1059 ◽

Cited By ~ 6

Author(s):

P. V. Strekalova ◽

Yu. A. Nagovitsyn ◽

A. Riehokainen ◽

V. V. Smirnova

Keyword(s):

Magnetic Field ◽

Small Scale ◽

Long Period ◽

Period Variations ◽

The Magnetic Field

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Mean-Field Magnetohydrodynamics as a Basis of Solar Dynamo Theory

Symposium - International Astronomical Union ◽

10.1017/s0074180900008287 ◽

1976 ◽

Vol 71 ◽

pp. 323-344 ◽

Cited By ~ 4

Author(s):

K.-H. Rädler

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Mean Field ◽

Strong Relationship ◽

Solar Radius ◽

Small Scale ◽

Dynamo Theory ◽

The Magnetic Field ◽

Complicated Situation ◽

Insight Into

One of the most striking features of both the magnetic field and the motions observed at the Sun is their highly irregular or random character which indicates the presence of rather complicated magnetohydrodynamic processes. Of great importance in this context is a comprehension of the behaviour of the large scale components of the magnetic field; large scales are understood here as length scales in the order of the solar radius and time scales of a few years. Since there is a strong relationship between these components and the solar 22-years cycle, an insight into the mechanism controlling these components also provides for an insight into the mechanism of the cycle. The large scale components of the magnetic field are determined not only by their interaction with the large scale components of motion. On the contrary, a very important part is played also by an interaction between the large and the small scale components of magnetic field and motion so that a very complicated situation has to be considered.

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Excitation of kinetic Alfvén turbulence by MHD waves and energization of space plasmas

Nonlinear Processes in Geophysics ◽

10.5194/npg-11-535-2004 ◽

2004 ◽

Vol 11 (5/6) ◽

pp. 535-543 ◽

Cited By ~ 23

Author(s):

Y. Voitenko ◽

M. Goossens

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Energy Transport ◽

Plasma Heating ◽

Alfven Wave ◽

Mhd Waves ◽

Space Plasmas ◽

Small Scale ◽

The Magnetic Field ◽

Dissipation Range

Abstract. There is abundant observational evidence that the energization of plasma particles in space is correlated with an enhanced activity of large-scale MHD waves. Since these waves cannot interact with particles, we need to find ways for these MHD waves to transport energy in the dissipation range formed by small-scale or high-frequency waves, which are able to interact with particles. In this paper we consider the dissipation range formed by the kinetic Alfvén waves (KAWs) which are very short- wavelengths across the magnetic field irrespectively of their frequency. We study a nonlocal nonlinear mechanism for the excitation of KAWs by MHD waves via resonant decay AW(FW)→KAW1+KAW2, where the MHD wave can be either an Alfvén wave (AW), or a fast magneto-acoustic wave (FW). The resonant decay thus provides a non-local energy transport from large scales directly in the dissipation range. The decay is efficient at low amplitudes of the magnetic field in the MHD waves, B/B0~10-2. In turn, KAWs are very efficient in the energy exchange with plasma particles, providing plasma heating and acceleration in a variety of space plasmas. An anisotropic energy deposition in the field-aligned degree of freedom for the electrons, and in the cross-field degrees of freedom for the ions, is typical for KAWs. A few relevant examples are discussed concerning nonlinear excitation of KAWs by the MHD wave flux and consequent plasma energization in the solar corona and terrestrial magnetosphere.

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Spatial scales and locality of magnetic helicity

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936675 ◽

2020 ◽

Vol 635 ◽

pp. A95 ◽

Cited By ~ 1

Author(s):

C. Prior ◽

G. Hawkes ◽

M. A. Berger

Keyword(s):

Magnetic Field ◽

Active Region ◽

Spectral Methods ◽

Wavelet Decomposition ◽

Spatial Scales ◽

Solar Interior ◽

Magnetic Helicity ◽

Clear Correlation ◽

Arbitrary Boundary ◽

The Magnetic Field

Context. Magnetic helicity is approximately conserved in resistive magnetohydrodynamic models. It quantifies the entanglement of the magnetic field within the plasma. The transport and removal of helicity is crucial in both dynamo development in the solar interior and active region evolution in the solar corona. This transport typically leads to highly inhomogeneous distributions of entanglement. Aims. There exists no consistent systematic means of decomposing helicity over varying spatial scales and in localised regions. Spectral helicity decompositions can be used in periodic domains and is fruitful for the analysis of homogeneous phenomena. This paper aims to develop methods for analysing the evolution of magnetic field topology in non-homogeneous systems. Methods. The method of multi-resolution wavelet decomposition is applied to the magnetic field. It is demonstrated how this decomposition can further be applied to various quantities associated with magnetic helicity, including the field line helicity. We use a geometrical definition of helicity, which allows these quantities to be calculated for fields with arbitrary boundary conditions. Results. It is shown that the multi-resolution decomposition of helicity has the crucial property of local additivity. We demonstrate a general linear energy-topology conservation law, which significantly generalises the two-point correlation decomposition used in the analysis of homogeneous turbulence and periodic fields. The localisation property of the wavelet representation is shown to characterise inhomogeneous distributions, which a Fourier representation cannot. Using an analytic representation of a resistive braided field relaxation, we demonstrate a clear correlation between the variations in energy at various length scales and the variations in helicity at the same spatial scales. Its application to helicity flows in a surface flux transport model show how various contributions to the global helicity input from active region field evolution and polar field development are naturally separated by this representation. Conclusions. The multi-resolution wavelet decomposition can be used to analyse the evolution of helicity in magnetic fields in a manner which is consistently additive. This method has the advantage over more established spectral methods in that it clearly characterises the inhomogeneous nature of helicity flows where spectral methods cannot. Further, its applicability in aperiodic models significantly increases the range of potential applications.

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Magnetospheric Processes Possibly Related to the Origin of Cosmic Rays

Symposium - International Astronomical Union ◽

10.1017/s0074180900074921 ◽

1981 ◽

Vol 94 ◽

pp. 373-391

Author(s):

Gerhard Haerendel

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Small Scale ◽

Shear Stresses ◽

Acceleration Process ◽

Dayside Magnetopause ◽

Field Lines ◽

The Magnetic Field ◽

Auroral Particles

Two processes are discussed which violate the frozen-in condition in a highly conducting plasma, reconnection and the auroral acceleration process. The first applies to situations in which . It plays an important role in the interaction of the solar wind with the Earth's magnetic field and controls energy input into as well as energetic particle release from the magnetosphere. Detailed in situ studies of the process on the dayside magnetopause reveal its transient and small-scale nature. The auroral acceleration process occurs in the low magnetosphere (β « 1) and accompanies sudden releases of magnetic shear stresses which exist in large-scale magnetospheric-ionospheric current circuits. The process is interpreted as a kind of breaking. The movements of the magnetospheric plasma which lead to a relief of the magnetic tensions occur in thin sheets and are decoupled along the magnetic field lines by parallel electric potential drops. It is this voltage that accelerates the primary auroral particles. The visible arcs are then traces of the magnetic breaking process at several 1000 km altitude.

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Approaching Earth’s core conditions in high-resolution geodynamo simulations

Geophysical Journal International ◽

10.1093/gji/ggz232 ◽

2019 ◽

Vol 219 (Supplement_1) ◽

pp. S137-S151 ◽

Cited By ~ 6

Author(s):

Julien Aubert

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Large Scale ◽

Small Scale ◽

Low Resolution ◽

Earth’S Core ◽

Earth's Core ◽

Density Anomaly ◽

Core Conditions ◽

The Magnetic Field

SUMMARY The geodynamo features a broad separation between the large scale at which Earth’s magnetic field is sustained against ohmic dissipation and the small scales of the turbulent and electrically conducting underlying fluid flow in the outer core. Here, the properties of this scale separation are analysed using high-resolution numerical simulations that approach closer to Earth’s core conditions than earlier models. The new simulations are obtained by increasing the resolution and gradually relaxing the hyperdiffusive approximation of previously published low-resolution cases. This upsizing process does not perturb the previously obtained large-scale, leading-order quasi-geostrophic (QG) and first-order magneto-Archimedes-Coriolis (MAC) force balances. As a result, upsizing causes only weak transients typically lasting a fraction of a convective overturn time, thereby demonstrating the efficiency of this approach to reach extreme conditions at reduced computational cost. As Earth’s core conditions are approached in the upsized simulations, Ohmic losses dissipate up to 97 per cent of the injected convective power. Kinetic energy spectra feature a gradually broadening self-similar, power-law spectral range extending over more than a decade in length scale. In this range, the spectral energy density profile of vorticity is shown to be approximately flat between the large scale at which the magnetic field draws its energy from convection through the QG-MAC force balance and the small scale at which this energy is dissipated. The resulting velocity and density anomaly planforms in the physical space consist in large-scale columnar sheets and plumes, respectively, co-existing with small-scale vorticity filaments and density anomaly ramifications. In contrast, magnetic field planforms keep their large-scale structure after upsizing. The small-scale vorticity filaments are aligned with the large-scale magnetic field lines, thereby minimizing the dynamical influence of the Lorentz force. The diagnostic outputs of the upsized simulations are more consistent with the asymptotic QG-MAC theory than those of the low-resolution cases that they originate from, but still feature small residual deviations that may call for further theoretical refinements to account for the structuring constraints of the magnetic field on the flow.

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Small scale observation of magnetopause motion: preliminary results of the INTERBALL project

Annales Geophysicae ◽

10.1007/s00585-997-0562-8 ◽

1997 ◽

Vol 15 (5) ◽

pp. 562-569 ◽

Cited By ~ 82

Author(s):

J. Safrankova ◽

G. Zastenker ◽

Z. Nemecek ◽

A. Fedorov ◽

M. Simersky ◽

...

Keyword(s):

Magnetic Field ◽

Time Resolution ◽

Simultaneous Measurement ◽

Small Scale ◽

Satellite Measurements ◽

Preliminary Results ◽

Plasma Device ◽

First Results ◽

The Magnetic Field ◽

Interball Project

Abstract. Two satellites of the INTERBALL project were launched on 3 August 1995. The main goals of the present paper are (1) to give a brief information about the VDP plasma device onboard the INTERBALL-1 satellite, (2) to present the Faradays cup data taken in different magnetospheric regions and (3) to expose first results of the two satellite measurements of the magnetopause motion. The presented data illustrate magnetopause crossings as seen by two satellites when separated by about ~ 1000 km. This separation combined with the Faraday's cup time resolution allows to estimate the velocity of the magnetopause and to reconstruct a possible structure of the boundary. Simultaneous measurement of the magnetic field supports the interpretation of the observed ion fluxes as a signature of the wavy motion of the boundary.

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Magnetic fields in turbulent quark matter and magnetar bursts

International Journal of Modern Physics D ◽

10.1142/s021827181750184x ◽

2017 ◽

Vol 27 (01) ◽

pp. 1750184 ◽

Cited By ~ 4

Author(s):

Maxim Dvornikov

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Quark Matter ◽

Electroweak Interaction ◽

Kinetic Equations ◽

Small Scale ◽

Chiral Magnetic Effect ◽

Dense Quark Matter ◽

Turbulence Effects ◽

The Magnetic Field

We analyze the magnetic field evolution in dense quark matter with unbroken chiral symmetry, which can be found inside quark and hybrid stars. The magnetic field evolves owing to the chiral magnetic effect in the presence of the electroweak interaction between quarks. In our study, we also take into account the magnetohydrodynamic turbulence effects in dense quark matter. We derive the kinetic equations for the spectra of the magnetic helicity density and the magnetic energy density as well as for the chiral imbalances. On the basis of the numerical solution of these equations, we find that turbulence effects are important for the behavior of small scale magnetic fields. It is revealed that, under certain initial conditions, these magnetic fields behave similarly to the electromagnetic flashes of some magnetars. We suggest that fluctuations of magnetic fields, described in frames of our model, which are created in the central regions of a magnetized compact star, can initiate magnetar bursts.

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Solar Wind Measurements from the Planetary Magnetometer Onboard the BepiColombo Spacecraft

10.5194/egusphere-egu2020-10707 ◽

2020 ◽

Author(s):

Daniel Heyner ◽

Ingo Richter ◽

Ferdinand Plaschke ◽

David Fischer ◽

Johannes Mieth ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Electric Propulsion ◽

Small Scale ◽

Solar Electric Propulsion ◽

Scientific Analysis ◽

Wind Measurements ◽

Propulsion Phase ◽

The Magnetic Field ◽

Magnetic Disturbances

BepiColombo is en-route to Mercury. The boom carrying the planetary magnetometers (MPO-MAG instrument) was deployed in space on 25th of October in 2018. After the deployment, the magnetic disturbances arising from the spacecraft have been greatly decreased. Since the deployment, the fluxgate sensors have been monitoring the magnetic field continuously except for the solar electric propulsion phase. Extensive calibration and data processing activities have since enabled us to greatly decrease spacecraft-generated disturbances in the magnetic field observations; these activities constitute a key step towards making the data suitable for scientific analysis. We present a few cases of identified magnetic disturbances, discuss the challenges they pose, and compare methods to clean the data. We also compare MPO-MAG measurements to observations by the Advanced Composition Explorer (ACE) solar wind monitor, thereby highlighting the small-scale nature and rapid evolution of interplanetary magnetic field (IMF) variations. We conclude with an overview of the scientific goals of the instrument team for the in-orbit mission phase.

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