scholarly journals On the Velocity Drift between Ions in the Solar Atmosphere

2020 ◽  
Vol 900 (2) ◽  
pp. 101
Author(s):  
Juan Martínez-Sykora ◽  
Mikolaj Szydlarski ◽  
Viggo H. Hansteen ◽  
Bart De Pontieu
Keyword(s):  
Solar Atmosphere ◽  
Velocity Drift

scholarly journals Mode conversion of two-fluid shocks in a partially-ionised, isothermal, stratified atmosphere

2020 ◽  
Vol 637 ◽  
pp. A97
Author(s):  
B. Snow ◽  
A. Hillier
Keyword(s):  
Solar Atmosphere ◽  
Mode Conversion ◽  
Frictional Heating ◽  
Fast Mode ◽  
Compressional Waves ◽  
Pressure Scale ◽  
Velocity Drift ◽  
Two Fluid ◽  
Lower Solar Atmosphere

Context. The plasma of the lower solar atmosphere consists of mostly neutral particles, whereas the upper solar atmosphere is mostly made up of ionised particles and electrons. A shock that propagates upwards in the solar atmosphere therefore undergoes a transition where the dominant fluid is either neutral or ionised. An upwards propagating shock also passes a point where the sound and Alfvén speed are equal. At this point the energy of the acoustic shock can separated into fast and slow components. The way the energy is distributed between the two modes depends on the angle of magnetic field. Aims. We aim to investigate the separation of neutral and ionised species in a gravitationally stratified atmosphere. The role of two-fluid effects on the structure of the shocks post-mode-conversion and the frictional heating is quantified for different levels of collisional coupling. Methods. Two-fluid numerical simulations were performed using the (PIP) code of a wave steepening into a shock in an isothermal, partially-ionised atmosphere. The collisional coefficient was varied to investigate the regimes where the plasma and neutral species are weakly, strongly, and finitely coupled. Results. The propagation speeds of the compressional waves hosted by neutral and ionised species vary and, therefore, velocity drift between the two species is produced as the plasma attempts to propagate faster than the neutrals. This is most extreme for a fast-mode shock. We find that the collisional coefficient drastically impacts the features present in the system, specifically the mode conversion height, type of shocks present, and the finite shock widths created by the two-fluid effects. In the finitely-coupled regime, fast-mode shock widths can exceed the pressure scale height, which may lead to a new potential observable of two-fluid effects in the lower solar atmosphere.

Ebysus, a Multi-Fluid Multi-Species (MFMS) code: Application to magnetic reconnection in the solar atmosphere

2021 ◽  
Author(s):  
Quentin Wargnier ◽  
Juan Martinez Sykora
Keyword(s):  
Magnetic Reconnection ◽  
Solar Atmosphere ◽  
Spatial Scales ◽  
Excited Level ◽  
High Energy ◽  
Momentum Exchange ◽  
Wide Range ◽  
Velocity Drift ◽  
Numerical Strategy ◽  
Non Equilibrium

<p>The solar atmosphere is composed of many species with a large number of ionization levels. Depending on the region considered, the plasma can be partially or fully ionized, weakly or strongly magnetized, weakly or strongly collisional, allowing for thermal non-equilibrium processes and chemical reactions. Recent observations of the IRIS mission (De Pontieu et al. 2014) have confirmed that the solar atmosphere is a complex environment involving a wide range of unsteady processes occurring at different temporal and spatial scales.</p><p>In this context, we have developed a new code Ebysus (see Martinez-Sykora et al., 2019), by expanding the state-of-the-art single-fluid radiative MHD code Bifrost (Gudiksen et al. 2011). Ebysus solves a full MultiFluid MultiSpecies (MFMS)  system of equation for any species and/or ionized/excited level as desired separately. Following Wargnier et al. 2020, an accurate description of the collisions for multicomponent plasmas in solar atmosphere conditions, consistent with the kinetic theory, has also been developed and implemented in the code. The code includes non-equilibrium (NEQ) ionization, recombination, excitation and de-excitation for any species, momentum exchange, electric forces due to velocity drift between different ionized species, thermal conduction and radiative losses. The whole numerical strategy has been tested and the modules needed for this proposal are fully implemented.</p><p>First, we will present the model and its numerical strategy. We will then focus on realistic magnetic reconnection (MR) events and perform numerical simulations in several conditions representative of different layers of the solar atmosphere. In particular, we will demonstrate the role of the drift velocities between different species on the reconnection rate and the formation of plasmoid instabilities, which leads to a high energy release. These instabilities play a significant role in the dynamics of chromospheric jets, as observed by IRIS (Rouppe et al. 2017). This strategy will be a crucial point in understanding MR events that occur during UV bursts or flares.</p>

Some Problems in Understanding the Solar Corona

1994 ◽  
Vol 144 ◽  
pp. 1-9
Author(s):  
A. H. Gabriel
Keyword(s):  
Solar Corona ◽  
Solar Atmosphere ◽  
Theoretical Modelling ◽  
Total System ◽  
Major Advance ◽  
X Ray ◽  
Proper Perspective ◽  
Space Observations

The development of the physics of the solar atmosphere during the last 50 years has been greatly influenced by the increasing capability of observations made from space. Access to images and spectra of the hotter plasma in the UV, XUV and X-ray regions provided a major advance over the few coronal forbidden lines seen in the visible and enabled the cooler chromospheric and photospheric plasma to be seen in its proper perspective, as part of a total system. In this way space observations have stimulated new and important advances, not only in space but also in ground-based observations and theoretical modelling, so that today we find a well-balanced harmony between the three techniques.

Influence of Magnetic Fields on Solar Hydrodynamics: Experimental Results

1977 ◽  
Vol 36 ◽  
pp. 143-180 ◽  
Author(s):  
J.O. Stenflo
Keyword(s):  
Solar Activity ◽  
Energy Balance ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
General Problem ◽  
Solar Rotation ◽  
Active Regions ◽  
Physical Conditions ◽  
Dynamic Phenomena

It is well-known that solar activity is basically caused by the Interaction of magnetic fields with convection and solar rotation, resulting in a great variety of dynamic phenomena, like flares, surges, sunspots, prominences, etc. Many conferences have been devoted to solar activity, including the role of magnetic fields. Similar attention has not been paid to the role of magnetic fields for the overall dynamics and energy balance of the solar atmosphere, related to the general problem of chromospheric and coronal heating. To penetrate this problem we have to focus our attention more on the physical conditions in the ‘quiet’ regions than on the conspicuous phenomena in active regions.

scholarly journals Determination of the Height of Hard X-Ray Sources in the Solar Atmosphere by Measurement of Photospheric Albedo Photons

1975 ◽  
Vol 68 ◽  
pp. 239-241
Author(s):  
John C. Brown ◽  
H. F. Van Beek
Keyword(s):  
Solar Atmosphere ◽  
The Other ◽  
X Ray ◽  
Theoretical Predictions ◽  
Source Models ◽  
The One

SummaryThe importance and difficulties of determining the height of hard X-ray sources in the solar atmosphere, in order to distinguish source models, have been discussed by Brown and McClymont (1974) and also in this Symposium (Brown, 1975; Datlowe, 1975). Theoretical predictions of this height, h, range between and 105 km above the photosphere for different models (Brown and McClymont, 1974; McClymont and Brown, 1974). Equally diverse values have been inferred from observations of synchronous chromospheric EUV bursts (Kane and Donnelly, 1971) on the one hand and from apparently behind-the-limb events (e.g. Datlowe, 1975) on the other.

Exploring the innermost solar atmosphere

2019 ◽  
Vol 4 (1) ◽  
pp. 19-20 ◽  
Author(s):  
Eugene N. Parker
Keyword(s):  
Solar Atmosphere
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