Magnetohydrodynamic Shocks and Solitons in the Solar Atmosphere: Recent Challenges in Observations and Theory (original) (raw)
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Dispersive shock waves in the solar wind
Astronomische Nachrichten, 2007
Compressional wavesinthe solar wind propagatingoverlarge distances are likelytosteepen into shock waveswhere the increase in the amplitude is balanced by dissipation. Dispersive effects caused by,e .g. Hall currents perpendicular to the ambient magnetic field can influence thegenerationand propagationo fshock waves. In thepresent study thedispersion is considered weak buti nt imei ts importance can grow. When thee ffect of dispersion is strong enough, it can balance thenonlinear steepening of wavesleading to the formation of solitons. The obtained results showthat theweak dispersion will alterthe amplitude and propagationspeed of theshock wave.
Propagation of a sausage soliton in the solar lower atmosphere observed by Hinode /SOT
Monthly Notices of the Royal Astronomical Society: Letters, 2010
Acoustic waves and pulses propagating from the solar photosphere upwards may quickly develop into shocks due to the rapid decrease of atmospheric density. However, if they propagate along a magnetic flux tube, then the nonlinear steepening may be balanced by tube dispersion effects. This may result in the formation of sausage soliton. The aim of this letter is to report an observational evidence of sausage soliton in the solar chromosphere. Time series of Ca II H line obtained at the solar limb with the Solar Optical Telescope (SOT) on the board of Hinode is analysed. Observations show an intensity blob, which propagates from 500 km to 1700 km above the solar surface with the mean apparent speed of 35 km s −1. The speed is much higher than expected local sound speed, therefore the blob can not be a simple pressure pulse. The blob speed, length to width ratio and relative intensity correspond to slow sausage soliton propagating along a magnetic tube. The blob width is increased with height corresponding to the magnetic tube expansion in the stratified atmosphere. Propagation of the intensity blob can be the first observational evidence of slow sausage soliton in the solar atmosphere.
Indications of shock waves in the solar photosphere
2000
High resolution observations of solar granulation near the solar limb are used in a search for hydrodynamic shocks caused by an abrupt braking of the fast (probably supersonic) horizontal flow of the granular plasma towards the intergranular lane. Shock signatures in the spectral line of Fe II 6456.38 Å of one particular observed shock event are investigated in detail. Evolution, amplitude, and spatial relation of the spectral line characteristics of the shock event are in agreement with predictions from numerical simulations for such shock phenomena in the solar photosphere. The dimensions and amplitudes of the observed shock signatures are comparable to predicted values when seeing and instrumental effects as well as a possible obliqueness of the shock front with respect to the observer's line-of-sight are taken into account. The temporal evolution of such an event is observed for the first time. The stable and declining phase of the event were studied for a time period of almost 2 min. A particular relationship was found between the shock event and a nearby G-band bright point located 2 from the shock event. It is suggestive that the observed shock is a causal consequence of the magnetic flux concentration, traced by the G-band bright point. Such a type of shock can appear outside the flux concentrations as a consequence of a rapid flux-tube motion.
Magnetohydrodynamic Fast Shocks and Their Relation to Solar Energetic Particle Event Intensities
Terrestrial, Atmospheric and Oceanic Sciences, 2013
Gradual solar energetic particles (SEPs) are associated with interplanetary (IP) shock driven by coronal mass ejections. Testing theories/models that are built around shock acceleration mechanisms is difficult due to the complexity of SEP fluxes acquired by single-point measurements. To circumvent this, we correlate fast-forward shock Mach numbers derived from a 1.5D magnetohydrodynamics simulation with the intensity of solar energetic oxygen (O) and helium-4 (4 He) particles acquired by instruments aboard the ACE spacecraft during a series of coronal mass ejections in 2003 (October 28-31). A good correlation at the 5% significance level is found for O and 4 He with energy (E) > ~10 MeV n-1 , with the peak correlation coefficient r = 0.82 for O (E = 63.8-89.8 MeV n-1) and r = 0.77 for 4 He (E = 18.0-29.4 MeV n-1), respectively, for hourly averaged data. This result not only bolsters the causal relationship between IP fast shocks and SEPs, but also suggests that the Mach number of IP shocks is one of the major controlling parameters for the intensity of SEPs measured in the near-Earth space.
Magnetohydrodynamic Shock Heating of the Solar Corona
The Astrophysical Journal, 2003
Coronal MHD waves excited by perturbations of magnetic field lines propagate upward, carrying with them the energy from the excitation. Under favorable conditions shocks form, and part of the wave energy is converted to plasma heating and motion. We use numerical simulations to accurately follow the shock formation and subsequent energy release. The model includes an adiabatic energy equation for the explicit evaluation of temperature increases and energy fluxes contributed by the shocks. Transverse, plane-polarized excitations are considered; they can be periodic, as in Alfvén wave trains, or pulsed, as might result from nanoflares. The model is tested with a set of validation runs that produce good agreement with theoretical predictions. Our results show that nonlinear waves moving along large magnetic fields with low plasma , with field amplitudes comparable to the background field, develop shocks that form important amounts of plasma heating and that mass outflow may occur. Fast and slow magnetoacoustic shocks are generated, each one making its own contribution. Most of the heating takes place in the low corona, but long-range distributed heating still occurs up to heights of several solar radii. The energy fluxes for the stronger cases are sufficient to compensate for thermal and convective losses, consistent with observations. We conclude that large-amplitude MHD shocks in low-regions could be a viable mechanism for coronal heating and wind acceleration in regions of open magnetic field lines.
Nonlinear evolution of slow waves in the solar wind
Journal of Geophysical Research, 1985
We show by numerical simulation using a hybrid code that comparison of the nonlinear steepening rate, calculated from fluid theory, with the linear collisionless damping rate, defines reasonably well the parameters for which fast and slow MHD waves should steepen. Our results indicate that, whereas fast modes should ordinarly steepen, steepened slow waves should occur rarely in the solar wind near 1 AU. INTRODUCTION The paucity of observations of slow mode shocks has been one of the mysteries of space plasma physics. Magnetohydrodynamic theory clearly predicts that slow mode shock pairs should be generated by magnetic field reconnec-,:.
Damping of magnetohydrodynamic waves by resonant absorption in the solar atmosphere
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2006
In the last decade we have been overwhelmed by an avalanche of discoveries of magnetohydrodynamic (MHD) waves by the Solar and Heliospheric Observatory and Transition Region and Coronal Explorer observatories. Both standing and propagating versions of fast magnetoacoustic and slow magnetoacoustic MHD waves have been detected. Information on the damping times and damping distances of these waves is less detailed and less accurate than that on periods and amplitudes. Nevertheless, observations show the damping times and damping lengths are often short. Also, different types of MHD waves in different types of magnetic structures likely require different damping mechanisms. The phenomenon of fast damping is well documented for the standing fast magnetosonic kink waves in coronal loops. This paper concentrates on standing fast magnetosonic waves. It reports on results on periods and damping times due to resonant absorption in one-dimensional and two-dimensional models of coronal loops. Special attention is given to multiple modes.
Nonlinear Development of Shocklike Structure in the Solar Wind
Physical Review Letters, 2009
We report first in situ multispacecraft observations of nonlinear steepening of compressional pulses in the solar wind upstream of Earth's bow shock. The magnetic field of a compressional pulse formed at the upstream edge of density holes is shown to suddenly break and steepen into a shocklike structure. During the early phase of development thermalization of ions is insignificant. Substantial thermalization of ions occurs as gyrating ions are observed at the steepened edge. These observations indicate that the mechanisms causing the dissipation of magnetic fields (currents) and ions are different in the early phase of shock development.
Advances in Space Research, 2018
This paper introduces an investigation of shocklike soliton or small amplitude Double Layers (DLs) in a collisionless plasma, consisting of positive and negative ions, nonthermal electrons, as well as solar wind streaming protons and electrons. Gardner equation is derived and its shocklike soliton solution is obtained. The model is employed to recognize a possible nonlinear wave at Venus ionosphere. The results indicate that the number densities and velocities of the streaming particles play crucial role to determine the polarity and characteristic features (amplitude and width) of the shocklike soliton waves. An electron streaming speed modifies a negative shocklike wave profile, while an ion streaming speed modulates a positive shocklike wave characteristic.
Fluid versus simulation model of solitons in solar wind: Application to Ulysses observations
Journal of Geophysical Research, 2007
1] This paper continues recent efforts based on Hall-MHD theory to explain a new class of magnetically compressive solitary structures in the interplanetary space, observed by the Ulysses magnetometer . The theoretical basis is extended by a kinetic approach via one-dimensional hybrid code simulations which reveal deficiencies of fluid theory in describing slow mode-type solitons in a collisionless finite b plasma. Kinetic solitary structures, resembling obliquely propagating Alfven wave pulses with quasi-circular or banana-type polarization are presented which may reproduce most of the observational features. This suggests that the soliton picture provides an adequate theoretical concept for the observed events.