scholarly journals The dynamics of 3-min wavefronts and their relation to sunspot magnetic fields

2020 ◽  
Vol 379 (2190) ◽  
pp. 20200180 ◽  
Author(s):  
Robert Sych ◽  
David B. Jess ◽  
Jiangtao Su
Keyword(s):  
Magnetic Field ◽  
Temporal Dynamics ◽  
Oscillation Period ◽  
Motion Path ◽  
Solar Dynamics Observatory ◽  
Digital Technique ◽  
Wave Dynamics ◽  
Mode Decomposition ◽  
Inclination Angles ◽  
Field Inclination

We present a study of wave processes occurring in solar active region NOAA 11131 on 10 December 2010, captured by the Solar Dynamics Observatory in the 1600 Å, 304 Å and 171 Å channels. For spectral analysis, we employed pixelized wavelet filtering together with a developed digital technique based on empirical mode decomposition. We studied the ∼3-minute wave dynamics to obtain relationships with the magnetic structuring of the underlying sunspot. We found that during development of wave trains the motion path occurred along a preferential direction, and that the broadband wavefronts can be represented as a set of separate narrowband oscillation sources. These sources become visible as the waves pass through the umbral inhomogeneities caused by the differing magnetic field inclination angles. We found the spatial and frequency fragmentation of wavefronts, and deduced that the combination of narrowband spherical and linear parts of the wavefronts provide the observed spirality. Maps of the magnetic field inclination angles confirm this assumption. We detect the activation of umbral structures as the increasing of oscillations in the sources along the front ridge. Their temporal dynamics are associated with the occurrence of umbral flashes. Spatial localization of the sources is stable over time and depends on the oscillation period. We propose that these sources are the result of wave paths along the loops extending outwards from the magnetic bundles of the umbra. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

Thermomagnetic convection in a layer of ferrofluid placed in a uniform oblique external magnetic field

2015 ◽  
Vol 764 ◽  
pp. 316-348 ◽  
Author(s):  
Habibur Rahman ◽  
Sergey A. Suslov
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Additional Parameter ◽  
Thermomagnetic Convection ◽  
Uniform External Magnetic Field ◽  
Inclination Angles ◽  
Convection Patterns ◽  
The Stability ◽  
The Magnetic Field ◽  
Field Inclination

AbstractLinear stability of magnetoconvection of a ferromagnetic fluid contained between two infinite differentially heated non-magnetic plates in the presence of an oblique uniform external magnetic field is studied in zero gravity conditions. The thermomagnetic convection that arises is caused by the spatial variation of magnetisation occurring due to its dependence on the temperature. The critical values of the governing parameters at which the transition between motionless and convective states is observed are determined for various field inclination angles and for fluid magnetic parameters that are consistently chosen from a realistic experimental range. It is shown that, similar to natural paramagnetic fluids, the most prominent convection patterns align with the in-layer component of the applied magnetic field but in contrast to such paramagnetic fluids the instability patterns detected in ferrofluids can be oscillatory. It is also found that, contrary to paramagnetic fluids, the stability characteristics of magnetoconvection in ferrofluids depend on the magnitude of the applied field which becomes an additional parameter of the problem. This is shown to be due to the nonlinearity of the magnetic field distribution within the ferrofluid.

Numerical study on the steady-state heat transfer rate of nanofluid filled within square cavity in the presence of oriented magnetic field

2013 ◽  
Vol 228 (8) ◽  
pp. 1348-1362 ◽  
Author(s):  
Masoud K Koopaee ◽  
Amir Omidvar ◽  
Iman Jelodari
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Inclination Angle ◽  
Transfer Rate ◽  
Solid Particles ◽  
Square Cavity ◽  
Inclination Angles ◽  
Rayleigh Numbers ◽  
Field Inclination

In this paper, the steady-state natural convection in a square cavity filled with water–Al2O3 nanofluid in the presence of magnetic fields with variable inclination angles is investigated numerically. The enclosure is subjected to different side-wall temperatures while the top and bottom walls are assumed to be adiabatic. The thermal behavior of enclosure is assessed using a finite volume-based computer program. In order to ensure the accuracy of results, comparisons are also made with a previous published work. In this research, at constant magnetic field strengths, the effect of magnetic field inclination angle on the rate of heat transfer in the square cavity is investigated at the Rayleigh numbers of Ra = 103, 104, 105 and 106. In this work, the Hartmann number ranges from Ha = 0 to 120 and the solid volume fraction varies from φ = 0 to 0.06. Numerical results show that depending on the Rayleigh and Hartmann numbers, the maximum heat transfer rate may occur at magnetic field inclination angles of 45°, 60° or 90° and the effect of magnetic field inclination angle is significant at high values of Rayleigh and Hartmann numbers. It is found that addition of nano-sized solid particles causes higher heat transfer rate when Ra = 103, whereas at Rayleigh number of Ra = 106, a reverse behavior is observed. Results show that at Rayleigh numbers of Ra = 104 and 105, the effect of solid particles addition on the thermal performance of the enclosure depends on the Hartmann number. It is also shown that an increase in the inclination angle causes higher velocity within the enclosure and addition of solid particles leads to suppression of flow field.

scholarly journals On the effect of oscillatory phenomena on Stokes inversion results

2020 ◽  
Vol 379 (2190) ◽  
pp. 20200182 ◽  
Author(s):  
P. H. Keys ◽  
O. Steiner ◽  
G. Vigeesh
Keyword(s):  
Magnetic Field ◽  
Solar Atmosphere ◽  
Solar Physics ◽  
Mhd Waves ◽  
Line Of Sight ◽  
Line Pair ◽  
Atmospheric Parameters ◽  
Wave Dynamics ◽  
Mode Decomposition ◽  
Wave Guides

Stokes inversion codes are crucial in returning properties of the solar atmosphere, such as temperature and magnetic field strength. However, the success of such algorithms to return reliable values can be hindered by the presence of oscillatory phenomena within magnetic wave guides. Returning accurate parameters is crucial to both magnetohydrodynamics (MHD) studies and solar physics in general. Here, we employ a simulation featuring propagating MHD waves within a flux tube with a known driver and atmospheric parameters. We invert the Stokes profiles for the 6301 Å and 6302 Å line pair emergent from the simulations using the well-known Stokes Inversions from Response functions code to see if the atmospheric parameters can be returned for typical spatial resolutions at ground-based observatories. The inversions return synthetic spectra comparable to the original input spectra, even with asymmetries introduced in the spectra from wave propagation in the atmosphere. The output models from the inversions match closely to the simulations in temperature, line-of-sight magnetic field and line-of-sight velocity within typical formation heights of the inverted lines. Deviations from the simulations are seen away from these height regions. The inversions results are less accurate during passage of the waves within the line formation region. The original wave period could be recovered from the atmosphere output by the inversions, with empirical mode decomposition performing better than the wavelet approach in this task. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

scholarly journals Spatio-temporal variability of the photospheric magnetic field

2010 ◽  
Vol 6 (S274) ◽  
pp. 204-206
Author(s):  
A. Vecchio ◽  
M. Laurenza ◽  
D. Meduri ◽  
V. Carbone ◽  
M. Storini
Keyword(s):  
Magnetic Field ◽  
Time Evolution ◽  
Empirical Mode Decomposition ◽  
Temporal Variability ◽  
Solar Magnetic Field ◽  
Temporal Dynamics ◽  
Heliographic Latitude ◽  
Preliminary Results ◽  
Mode Decomposition ◽  
Spatio Temporal

AbstractThe spatio-temporal dynamics of the solar magnetic field has been investigated by using NSO/Kitt Peak synoptic magnetic maps covering ~28 yr. For each heliographic latitude the field has been analyzed through the Empirical Mode Decomposition, in order to investigate the time evolution of the various characteristic oscillating frequencies. Preliminary results are discussed.

scholarly journals Levitation of non-magnetizable droplet inside ferrofluid

2018 ◽  
Vol 857 ◽  
pp. 398-448 ◽  
Author(s):  
Chamkor Singh ◽  
Arup K. Das ◽  
Prasanta K. Das
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Viscosity Ratio ◽  
Temporal Dynamics ◽  
Liquid Droplet ◽  
Droplet Surface ◽  
Two Dimensions ◽  
Projection Algorithm ◽  
The Stability ◽  
The Individual

The central theme of this work is that a stable levitation of a denser non-magnetizable liquid droplet, against gravity, inside a relatively lighter ferrofluid – a system barely considered in ferrohydrodynamics – is possible, and exhibits unique interfacial features; the stability of the levitation trajectory, however, is subject to an appropriate magnetic field modulation. We explore the shapes and the temporal dynamics of a plane non-magnetizable droplet levitating inside a ferrofluid against gravity due to a spatially complex, but systematically generated, magnetic field in two dimensions. The coupled set of Maxwell’s magnetostatic equations and the flow dynamic equations is integrated computationally, utilizing a conservative finite-volume-based second-order pressure projection algorithm combined with the front-tracking algorithm for the advection of the interface of the droplet. The dynamics of the droplet is studied under both the constant ferrofluid magnetic permeability assumption as well as for more realistic field-dependent permeability described by Langevin’s nonlinear magnetization model. Due to the non-homogeneous nature of the magnetic field, unique shapes of the droplet during its levitation, and at its steady state, are realized. The complete spatio-temporal response of the droplet is a function of the Laplace number $La$ , the magnetic Laplace number $La_{m}$ and the Galilei number $Ga$ ; through detailed simulations we separate out the individual roles played by these non-dimensional parameters. The effect of the viscosity ratio, the stability of the levitation path and the possibility of existence of multiple stable equilibrium states is investigated. We find, for certain conditions on the viscosity ratio, that there can be developments of cusps and singularities at the droplet surface; we also observe this phenomenon experimentally and compare with the simulations. Our simulations closely replicate the singular projection on the surface of the levitating droplet. Finally, we present a dynamical model for the vertical trajectory of the droplet. This model reveals a condition for the onset of levitation and the relation for the equilibrium levitation height. The linearization of the model around the steady state captures that the nature of the equilibrium point goes under a transition from being a spiral to a node depending upon the control parameters, which essentially means that the temporal route to the equilibrium can be either monotonic or undulating. The analytical model for the droplet trajectory is in close agreement with the detailed simulations.

scholarly journals Improvement of the Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Inversion Code

2021 ◽  
Vol 923 (1) ◽  
pp. 84
Author(s):  
Ana Belén Griñón-Marín ◽  
Adur Pastor Yabar ◽  
Yang Liu ◽  
J. Todd Hoeksema ◽  
Aimee Norton
Keyword(s):  
Magnetic Field ◽  
Field Vector ◽  
Magnetic Field Vector ◽  
Solar Dynamics Observatory ◽  
Filling Fraction ◽  
Resolution Element ◽  
New Strategy ◽  
Moderate Field ◽  
Solar Dynamics ◽  
Field Strengths

Abstract A spectral line inversion code, Very Fast Inversion of the Stokes Vector (VFISV), has been used since 2010 May to infer the solar atmospheric parameters from the spectropolarimetric observations taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. The magnetic filling factor, the fraction of the surface with a resolution element occupied by magnetic field, is set to have a constant value of 1 in the current version of VFISV. This report describes an improved inversion strategy for the spectropolarimetric data observed with HMI for magnetic field strengths of intermediate values in areas spatially not fully resolved. The VFISV inversion code has been modified to enable inversion of the Stokes profiles with two different components: one magnetic and one nonmagnetic. In this scheme, both components share the atmospheric components except for the magnetic field vector. In order to determine whether the new strategy is useful, we evaluate the inferred parameters inverted with one magnetic component (the original version of the HMI inversion) and with two components (the improved version) using a Bayesian analysis. In pixels with intermediate magnetic field strengths (e.g., plages), the new version provides statistically significant values of filling fraction and magnetic field vector. Not only does the fitting of the Stokes profile improve, but also the inference of the magnetic parameters and line-of-sight velocity are obtained uniquely. The new strategy is also proven to be effective for mitigating the anomalous hemispheric bias in the east–west magnetic field component in moderate field regions.

The magnetic structure and dynamics of a decaying active region

2019 ◽  
Vol 15 (S354) ◽  
pp. 53-57
Author(s):  
Ioannis Kontogiannis ◽  
Christoph Kuckein ◽  
Sergio Javier González Manrique ◽  
Tobias Felipe ◽  
Meetu Verma ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Time Series ◽  
High Resolution ◽  
Active Region ◽  
Magnetic Structure ◽  
High Velocity ◽  
Solar Dynamics Observatory ◽  
Multi Wavelength ◽  
Convective Motions ◽  
Field Lines

AbstractWe study the evolution of the decaying active region NOAA 12708, from the photosphere up to the corona using high resolution, multi-wavelength GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph (GRIS), spectral imaging time-series in the Na ID2 spectral line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context imaging in the Ca IIH and blue continuum by the High-resolution Fast Imager (HiFI). Context imaging in the UV/EUV from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) complements our dataset. The region under study contains one pore with a light-bridge, a few micro-pores and extended clusters of magnetic bright points. We study the magnetic structure from the photosphere up to the upper chromosphere through the spectropolarimetric observations in He II and Si I and through the magnetograms provided by the Helioseismic and Magnetic Imager (HMI). The high-resolution photospheric images reveal the complex interaction between granular-scale convective motions and a range of scales of magnetic field concentrations in unprecedented detail. The pore itself shows a strong interaction with the convective motions, which eventually leads to its decay, while, under the influence of the photospheric flow field, micro-pores appear and disappear. Compressible waves are generated, which are guided towards the upper atmosphere along the magnetic field lines of the various magnetic structures within the field-of-view. Modelling of the He i absorption profiles reveals high velocity components, mostly associated with magnetic bright points at the periphery of the active region, many of which correspond to asymmetric Si I Stokes-V profiles revealing a coupling between upper photospheric and upper chromospheric dynamics. Time-series of Na ID2 spectral images reveal episodic high velocity components at the same locations. State-of-the-art multi-wavelength GREGOR observations allow us to track and understand the mechanisms at work during the decay phase of the active region.

scholarly journals Exponentially decaying modes and long-term prediction of sea ice concentration using Koopman mode decomposition

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
James Hogg ◽  
Maria Fonoberova ◽  
Igor Mezić
Keyword(s):  
Sea Ice ◽  
Annual Variation ◽  
Temporal Dynamics ◽  
The Arctic ◽  
Sea Ice Concentration ◽  
Mode Decomposition ◽  
Spatial Modes ◽  
Ice Concentration ◽  
The Mean ◽  
Insight Into

Abstract Sea ice cover in the Arctic and Antarctic is an important indicator of changes in the climate, with important environmental, economic and security consequences. The complexity of the spatio-temporal dynamics of sea ice makes it difficult to assess the temporal nature of the changes—e.g. linear or exponential—and their precise geographical loci. In this study, Koopman Mode Decomposition (KMD) is applied to satellite data of sea ice concentration for the Northern and Southern hemispheres to gain insight into the temporal and spatial dynamics of the sea ice behavior and to predict future sea ice behavior. We observe spatial modes corresponding to the mean and annual variation of Arctic and Antarctic sea ice concentration and observe decreases in the mean sea ice concentration from early to later periods, as well as corresponding shifts in the locations that undergo significant annual variation in sea ice concentration. We discover exponentially decaying spatial modes in both hemispheres and discuss their precise spatial extent, and also perform predictions of future sea ice concentration. The Koopman operator-based, data-driven decomposition technique gives insight into spatial and temporal dynamics of sea ice concentration not apparent in traditional approaches.

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