The effects of driving time scales on heating in a coronal arcade

Context. The relative importance of alternating current (AC) and direct current (DC) heating mechanisms in maintaining the temperature of the solar corona is not well constrained. Aims. We aim to investigate the effects of the characteristic time scales of photospheric driving on the injection and dissipation of magnetic and kinetic energy within a coronal arcade. Methods. We conducted three-dimensional magnetohydrodynamic simulations of complex foot point driving imposed on a potential coronal arcade. We modified the typical time scales associated with the velocity driver to understand the efficiency of heating obtained using AC and DC drivers. We considered the implications for the injected Poynting flux and the spatial and temporal nature of the energy release in dissipative regimes. Results. For the same driver amplitude and complexity, long time scale velocity motions are able to inject a much greater Poynting flux of energy into the corona. Consequently, in non-ideal regimes, slow stressing motions result in a greater increase in plasma temperature than for wave-like driving. In dissipative simulations, Ohmic heating is found to be much more significant than viscous heating. For all drivers in our parameter space, energy dissipation is greatest close to the base of the arcade, where the magnetic field strength is strongest, and at separatrix surfaces, where the field connectivity changes. Across all simulations, the background field is stressed with random foot point motions (in a manner more typical of DC heating studies), and, even for short time scale driving, the injected Poynting flux is large given the small amplitude flows considered. For long time scale driving, the rate of energy injection was comparable to the expected requirements in active regions. The heating rates were found to scale with the perturbed magnetic field strength and not the total field strength. Conclusions. Alongside recent studies that show that power within the corona is dominated by low frequency motions, our results suggest that, in the closed corona, DC heating is more significant than AC heating.

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Stratified Flows over and around Long Dynamically Tall Mountain Ridges

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0145.1 ◽

2019 ◽

Vol 76 (5) ◽

pp. 1265-1287 ◽

Cited By ~ 2

Author(s):

Arjun Jagannathan ◽

Kraig Winters ◽

Laurence Armi

Keyword(s):

Time Scales ◽

Time Scale ◽

Stratified Flows ◽

Half Width ◽

Short Time Scale ◽

Late Time ◽

Low Level ◽

Long Time ◽

Flow Splitting ◽

Short Time

Abstract Uniformly stratified flows approaching long and dynamically tall ridges develop two distinct flow components over disparate time scales. The fluid upstream and below a “blocking level” is stagnant in the limit of an infinite ridge and flows around the sides when the ridge extent is finite. The streamwise half-width of the obstacle at the blocking level arises as a natural inner length scale for the flow, while the excursion time over this half-width is an associated short time scale for the streamwise flow evolution. Over a longer time scale, low-level horizontal flow splitting leads to the establishment of an upstream layerwise potential flow beneath the blocking level. We demonstrate through numerical experiments that for sufficiently long ridges, crest control and streamwise asymmetry are seen on both the short and long time scales. On the short time scale, upstream blocking is established quickly and the flow is well described as a purely infinite-ridge overflow. Over the long time scale associated with flow splitting, low-level flow escapes around the sides, but the overflow continues to be hydraulically controlled and streamwise asymmetric in the neighborhood of the crest. We quantify this late-time overflow by estimating its volumetric transport and then briefly demonstrate how this approach can be extended to predict the overflow across nonuniform ridge shapes.

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Variations of interplanetary magnetic field on various long time-scales

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3594 ◽

2019 ◽

Vol 492 (2) ◽

pp. 1914-1918

Author(s):

Yury A Nagovitsyn ◽

Aleksandra A Osipova

Keyword(s):

Magnetic Field ◽

Solar Activity ◽

Interplanetary Magnetic Field ◽

Time Scales ◽

Sunspot Number ◽

Time Scale ◽

Wavelet Transformation ◽

B Values ◽

Group Sunspot Number ◽

Long Time

ABSTRACT The IDV index of geomagnetic activity is used by many researchers as a proxy of the interplanetary magnetic field (IMF) strength B. Using the original multiscale regression (MSR) method based on wavelet transformation, we obtained a long series of B values starting from 1845. Then, based on the new 2.0 versions of the sunspot number and group sunspot number and using MSR method and this series as a reference, we reconstructed IMF strength B starting from 1610. Further extension of the reconstruction is associated with radiocarbon reconstructions of solar activity at a time-scale of up to several millennia. It is shown that in the last 3200 yr the IMF strength has been experiencing a downward trend of −(0.39 ± 0.17) · 10−3 nT· yr−1.

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Investigating the anatomy of magnetosheath jets – MMS observations

Annales Geophysicae ◽

10.5194/angeo-36-655-2018 ◽

2018 ◽

Vol 36 (2) ◽

pp. 655-677 ◽

Cited By ~ 5

Author(s):

Tomas Karlsson ◽

Ferdinand Plaschke ◽

Heli Hietala ◽

Martin Archer ◽

Xóchitl Blanco-Cano ◽

...

Keyword(s):

Magnetic Field ◽

Field Strength ◽

Magnetic Field Strength ◽

Electromagnetic Waves ◽

Dynamic Pressure ◽

Lower Hybrid ◽

Electrostatic Waves ◽

Poynting Flux ◽

Generation Mechanisms ◽

Two Jets

Abstract. We use Magnetosphere Multiscale (MMS) mission data to investigate a small number of magnetosheath jets, which are localized and transient increases in dynamic pressure, typically due to a combined increase in plasma velocity and density. For two approximately hour-long intervals in November, 2015 we found six jets, which are of two distinct types. (a) Two of the jets are associated with the magnetic field discontinuities at the boundary between the quasi-parallel and quasi-perpendicular magnetosheath. Straddling the boundary, the leading part of these jets contains an ion population similar to the quasi-parallel magnetosheath, while the trailing part contains ion populations similar to the quasi-perpendicular magnetosheath. Both populations are, however, cooler than the surrounding ion populations. These two jets also have clear increases in plasma density and magnetic field strength, correlated with a velocity increase. (b) Three of the jets are found embedded within the quasi-parallel magnetosheath. They contain ion populations similar to the surrounding quasi-parallel magnetosheath, but with a lower temperature. Out of these three jets, two have a simple structure. For these two jets, the increases in density and magnetic field strength are correlated with the dynamic pressure increases. The other jet has a more complicated structure, and no clear correlations between density, magnetic field strength and dynamic pressure. This jet has likely interacted with the magnetosphere, and contains ions similar to the jets inside the quasi-parallel magnetosheath, but shows signs of adiabatic heating. All jets are associated with emissions of whistler, lower hybrid, and broadband electrostatic waves, as well as approximately 10 s period electromagnetic waves with a compressional component. The latter have a Poynting flux of up to 40 µW m−2 and may be energetically important for the evolution of the jets, depending on the wave excitation mechanism. Only one of the jets is likely to have modified the surrounding magnetic field into a stretched configuration, as has recently been reported in other studies. None of the jets are associated with clear signatures of either magnetic or thermal pressure gradient forces acting on them. The different properties of the two types also point to different generation mechanisms, which are discussed here. Their different properties and origins suggest that the two types of jets need to be separated in future statistical and simulation studies. Keywords. Magnetospheric physics (magnetosheath; plasma waves and instabilities; solar wind–magnetosphere interactions)

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Origin of Blazar Activity

Symposium - International Astronomical Union ◽

10.1017/s0074180900162084 ◽

1999 ◽

Vol 194 ◽

pp. 256-268

Author(s):

M. M. Romanova

Keyword(s):

Magnetic Field ◽

Black Hole ◽

Energy Spectrum ◽

Magnetic Fields ◽

Time Scale ◽

High Frequency ◽

Short Time Scale ◽

Poynting Flux ◽

Electron Positron ◽

Short Time

Models of Blazars based on the propagation of finite discontinuities or fronts in the Poynting flux jet from the innermost regions of an accretion disk around a black hole are discussed. Such fronts may be responsible for short time–scale (from less than hours to days) flares in different wavebands from high frequency radioband to TeV, with delay in low radio frequencies as a result of synchrotron self-absorption. The cases of magnetic fields of one and opposite polarities across the front are investigated. We find that annihilation of magnetic field in the front leads to higher energy spectrum of leptons and possibility of strong TeV flares. Electron–positron pairs form in most cases as a result of interaction between numerous synchrotron photons and SSC photons, and constitute the majority species, compared with the ions at subparsec scales. Frequent weak outbursts may be responsible for flickering core radiation in all wavebands, while the stronger outbursts may be observed as short time–scale flares.

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On the Configuration of the Magnetic Field of β CrB

International Astronomical Union Colloquium ◽

10.1017/s0252921100080933 ◽

1976 ◽

Vol 32 ◽

pp. 613-622

Author(s):

I.A. Aslanov ◽

Yu.S. Rustamov

Keyword(s):

Magnetic Field ◽

Field Strength ◽

Radial Velocity ◽

Magnetic Field Strength ◽

Complex Shape ◽

Rotation Period ◽

Field Variation ◽

Magnetic Field Variation ◽

Secular Variations ◽

The Magnetic Field

SummaryMeasurements of the radial velocities and magnetic field strength of β CrB were carried out. It is shown that there is a variability with the rotation period different for various elements. The curve of the magnetic field variation measured from lines of 5 different elements: FeI, CrI, CrII, TiII, ScII and CaI has a complex shape specific for each element. This may be due to the presence of magnetic spots on the stellar surface. A comparison with the radial velocity curves suggests the presence of a least 4 spots of Ti and Cr coinciding with magnetic spots. A change of the magnetic field with optical depth is shown. The curve of the Heffvariation with the rotation period is given. A possibility of secular variations of the magnetic field is shown.

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Suppress of neurotransduction in injured spinal cord of rats with moderate magnetic field strength

Neuroscience Research ◽

10.1016/s0168-0102(00)81259-6 ◽

2000 ◽

Vol 38 ◽

pp. S69

Author(s):

H Tatsuoka

Keyword(s):

Magnetic Field ◽

Spinal Cord ◽

Field Strength ◽

Magnetic Field Strength ◽

Injured Spinal Cord ◽

Moderate Magnetic Field

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2D analysis of magnetic field strength in GO SiFe steel sheets

Journal de Physique IV (Proceedings) ◽

10.1051/jp4:19982133 ◽

1998 ◽

Vol 08 (PR2) ◽

pp. Pr2-579-Pr2-582 ◽

Cited By ~ 1

Author(s):

S. Tumanski ◽

M. Stabrowski

Keyword(s):

Magnetic Field ◽

Field Strength ◽

Magnetic Field Strength ◽

Steel Sheets

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MAGNETIC FIELD, PRESSURE AND TEMPERATURE DEPENDENT OPTICAL PROPERTIES IN A GaAs 9.0 P 1.0 QUANTUM DOT

JOURNAL OF ADVANCES IN PHYSICS ◽

10.24297/jap.v6i2.1791 ◽

2014 ◽

Vol 6 (2) ◽

pp. 1178-1190

Author(s):

A. JOHN PETER ◽

Ada Vinolin

Keyword(s):

Magnetic Field ◽

Optical Properties ◽

Quantum Dot ◽

Field Strength ◽

Magnetic Field Strength ◽

Photon Energy ◽

Nonlinear Optical ◽

Binding Energies ◽

Nonlinear Optical Properties ◽

Optical Rectification

Simultaneous effects of magnetic field, pressure and temperature on the exciton binding energies are found in a 9.0 1.0 6.0 4.0 GaAs P / GaAs P quantum dot. Numerical calculations are carried out taking into consideration of spatial confinement effect. The cylindrical system is taken in the present problem with the strain effects. The electronic properties and the optical properties are found with the combined effects of magnetic field strength, hydrostatic pressure and temperature values. The exciton binding energies and the nonlinear optical properties are carried out taking into consideration of geometrical confinement and the external perturbations.Compact density approach is employed to obtain the nonlinear optical properties. The optical rectification coefficient is obtained with the photon energy in the presence of pressure, temperature and external magnetic field strength. Pressure and temperature dependence on nonlinear opticalÂ susceptibilities of generation of second and third order harmonics as a function of incident photon energy are brought out in the influence of magnetic field strength. The result shows that the electronic and nonlinear optical properties are significantly modified by the applications of external perturbations in a 9.0 1.0 6.0 4.0 GaAs P / GaAs P quantum dot.

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