Acceleration of Plasma Flows in the Solar Atmosphere Due to Magnetofluid Coupling - Simulation and Analysis (original) (raw)
Related papers
2005
Within the framework of a two–fluid description possible pathways for the generation of fast flows (dynamical as well as steady) in the lower solar atmosphere is established. It is shown that a primary plasma flow (locally sub– Alfvénic) is accelerated when interacting with emerging/ambient arcade–like closed field structures. The acceleration implies a conversion of thermal and field energies to kinetic energy of the flow. The time–scale for creating reasonably fast flows (& 100 km/s) is dictated by the initial ion skin depth while the amplification of the flow depends on local β. It is shown, for the first time, that distances over which the flows become ”fast” are ∼ 0.01 Rs from the interaction surface; later the fast flow localizes (with dimensions . 0.05 RS) in the upper central region of the original arcade. For fixed initial temperature the final speed (& 500 km/s) of the accelerated flow, and the modification of the field structure are independent of the time-duration (life–...
Generation of Flows in the Solar Atmosphere Due to Magnetofluid Coupling
The Astrophysical Journal, 2002
It is shown that a generalized magneto-Bernoulli mechanism can effectively generate high velocity flows in the Solar chromosphere by transforming the plasma pressure energy into kinetic energy. It is found that at reasonable heights and for realistic plasma parameters, there is a precipitous pressure fall accompanied by a sharp amplification of the flow speed.
Acceleration of plasma flows in the closed magnetic fields: Simulation and analysis
Physics of Plasmas, 2006
Within the framework of a two-fluid description, possible pathways for the generation of fast flows ͑dynamical as well as steady͒ in the closed magnetic fields are established. It is shown that a primary plasma flow ͑locally sub-Alfvénic͒ is accelerated while interacting with ambient arcade-like closed field structures. The time scale for creating reasonably fast flows ͑տ100 km/ s͒ is dictated by the initial ion skin depth, while the amplification of the flow depends on local plasma . It is shown that distances over which the flows become "fast" are ϳ0.01R 0 from the interaction surface ͑R 0 being a characteristic length of the system͒; later, the fast flow localizes ͑with dimensions Շ0.05R 0 ͒ in the upper central region of the original arcade. For fixed initial temperature, the final speed ͑տ500 km/ s͒ of the accelerated flow and the modification of the field structure are independent of the time duration ͑lifetime͒ of the initial flow. In the presence of dissipation, these flows are likely to play a fundamental role in the heating of the finely structured stellar atmospheres; their relevance to the solar wind is also obvious. Recent observations, for instance, suggest that the energy source for solar coronal heating is very likely a byproduct of the outflow of heat from Sun's interior through the convection zone. The convection zone acts as a heat engine, converting some of the thermal energy into mechanical ͑flow͒ and magnetic energy; a part of this energy ͑mechanical and magnetic͒ enters the corona, and finally dissipates into heat. Thus, one of the possible sources for the eventual heating of the corona could be the kinetic energy in the flows which were created and energized somewhere in the lower parts of the solar atmosphere.
Generation of Flows in the Solar Chromosphere Due to Magnetofluid Coupling
2002
It is shown that a generalized magneto-Bernoulli mechanism can effectively generate high velocity flows in the Solar chromosphere by transforming the plasma pressure energy into kinetic energy. It is found that at reasonable heights and for realistic plasma parameters, there is a precipitous pressure fall accompanied by a sharp amplification of the flow speed.
Kinetic models for space plasmas: Recent progress for the solar wind and the Earth’s magnetosphere
2016
Recent models for the solar wind and the inner magnetosphere have been developed using the kinetic approach. The solution of the evolution equation is used to determine the velocity distribution function of the particles and their moments. The solutions depend on the approximations and assumptions made in the development of the models. Effects of suprathermal particles often observed in space plasmas are taken into account to show their influence on the characteristics of the plasma, with specific applications for coronal heating and solar wind acceleration. We describe in particular the results obtained with the collisionless exospheric approximation based on the Lorentzian velocity distribution function for the electrons and its recent progress in three dimensions. The effects of Coulomb collisions obtained by using a Fokker-Planck term in the evolution equation were also investigated, as well as effects of the whistler wave turbulence at electron scale and the kinetic Alfven waves at the proton scale. For solar wind especially, modelling efforts with both magnetohydrodynamic and kinetic treatments have been compared and combined in order to improve the predictions in the vicinity of the Earth. Photospheric magnetograms serve as observational input in semi-empirical coronal models used for estimating the plasma characteristics up to coronal heliocentric distances taken as boundary conditions in solar wind models. The solar wind fluctuations may influence the dynamics of the space environment of the Earth and generate geomagnetic storms. In the magnetosphere of the Earth, the trajectories of the particles are simulated to study the plasmasphere, the extension of the ionosphere along closed magnetic field lines and to better understand the physical mechanisms involved in the radiation belts dynamics. Kinetic models have been developed to give a microscopic description of space plasmas that is extremely useful in such rarefied environments. Indeed, the velocity distribution functions f(r,v,t) of the particles (where r, v and t are, respectively, the position and the velocity of the particles, and the time) are generally non-Maxwellian and anisotropic in low density plasmas where the collisions are rare. The distributions are often observed to decrease as a power law of the square velocity instead of exponentially and thus to have more suprathermal particles in their tails. This is illustrated in Fig. 1 for the electrons observed in situ in the solar wind, here at 2.7 AU by ULYSSES. This excess of suprathermal particles is
Weak Turbulence Cascading Effects in the Acceleration and Heating of Ions in the Solar Wind
The Astrophysical Journal, 2014
We study the wave-particle interaction and the evolution of electromagnetic waves propagating through a solarwind-like plasma composed of cold electrons, isotropic protons, and a small portion of drifting anisotropic He +2 (T ⊥α = 6 T α ) and O +6 (T ⊥O = 11 T O ) ions as suggested in Gomberoff & Valdivia and Gomberoff et al., using two approaches. First, we use quasilinear kinetic theory to study the energy transfer between waves and particles, with the subsequent acceleration and heating of ions. Second, 1.5 D (one spatial dimension and three dimensions in velocity space) hybrid numerical simulations are performed to investigate the fully nonlinear evolution of this wave-particle interaction. Numerical results of both approaches show that the temperatures of all species evolve anisotropically, consistent with the time-dependent wave-spectrum energy. In a cascade effect, we observe the emergence of modes at frequencies higher than those initially considered, peaking at values close to the resonance frequencies of O +6 ions (ω ∼ Ω cO ) and He +2 ions (ω ∼ Ω cα ), being the peak due to O +6 ions about three times bigger than the peak associated with He +2 ions. Both the heating of the plasma and the energy cascade were more efficient in the nonlinear analysis than in the quasilinear one. These results suggest that this energy cascade mechanism may participate in the acceleration and heating of the solar wind plasma close to the Sun during fast streams associated with coronal holes.
The Kinetic Treatment of Space Plasmas
AIP Conference Proceedings, 2003
To describe transport in space plasmas hydrodynamic and kinetic approaches have been proposed and used. These approaches are appropriate for separate collisional regimes. Hydrodynamics is a valid approximation of the general transport equations in highly collision-dominated fluids. In low-density plasmas where the Knudsen number is larger than 1 like at high altitude in planetary and stellar exospheres, only a kinetic treatment is appropriate. Collisionless models of the high altitude planetary atmospheres have been first based on the solution of the Liouville-Vlasov equation. They proved to be very useful zero-order kinetic approximations since they have demonstrated the importance of the internal polarization electric field in the acceleration process of the solar wind and polar wind protons. Higher order kinetic approximations have been more recently developed. Numerical solutions of the Fokker-Planck equation for the velocity distribution of the electrons in the solar wind and H + ions in the polar wind have now been obtained. The major and key differences between the results of these different approaches are illustrated through solar wind and terrestrial polar wind applications with comparison of the particle velocity distribution functions found in the different models.
Particle acceleration and heating in a turbulent solar corona
Plasma Physics and Controlled Fusion
Turbulence, magnetic reconnection, and shocks can be present in explosively unstable plasmas, forming a new electromagnetic environment, which we call here turbulent reconnection, and where spontaneous formation of current sheets takes place. We will show that the heating and the acceleration of particles is the result of the synergy of stochastic (second order Fermi) and systematic (first order Fermi) acceleration inside fully developed turbulence. The solar atmosphere is magnetically coupled to a turbulent driver (the convection zone), therefore the appearance of turbulent reconnection in the solar atmosphere is externally driven. Turbulent reconnection, once it is established in the solar corona, drives the coronal heating and particle acceleration.
Astronomy & Astrophysics, 2011
We aim at investigating the formation of jet-like features in the lower solar atmosphere, e.g. chromosphere and transition region, as a result of magnetic reconnection. Magnetic reconnection as occurring at chromospheric and transition regions densities and triggered by magnetic flux emergence is studied using a 2.5D MHD code. The initial atmosphere is static and isothermal, with a temperature of 20,000 K. The initial magnetic field is uniform and vertical. Two physical environments with different magnetic field strength (25 G and 50 G) are presented. In each case, two sub-cases are discussed, where the environments have different initial mass density. In the case where we have a weaker magnetic field (25 G) and higher plasma density ($N_e=2\times 10^{11}$ cm$^{-3}$), valid for the typical quiet Sun chromosphere, a plasma jet would be observed with a temperature of 2--3 times104\times 10^4times104 K and a velocity as high as 40 km/s. The opposite case of a medium with a lower electron density ($N_e=2\times 10^{10}$ cm$^{-3}$), i.e. more typical for the transition region, and a stronger magnetic field of 50 G, up-flows with line-of-sight velocities as high as 90 km/s and temperatures of 6 times\timestimes 10$^5$ K, i.e. upper transition region -- low coronal temperatures, are produced. Only in the latter case, the low corona Fe IX 171 \AA\ shows a response in the jet which is comparable to the O V increase. The results show that magnetic reconnection can be an efficient mechanism to drive plasma outflows in the chromosphere and transition region. The model can reproduce characteristics, such as temperature and velocity for a range of jet features like a fibril, a spicule, an hot X-ray jet or a transition region jet by changing either the magnetic field strength or the electron density, i.e. where in the atmosphere the reconnection occurs.