Coronal heating in coupled photosphere-chromosphere-coronal systems: turbulence and leakage

Coronal loops act as resonant cavities for low frequency fluctuations that are transmitted from the deeper layers of the solar atmosphere and are amplified in the corona, triggering nonlinear interactions. However trapping is not perfect, some energy leaks down to the chromosphere, thus limiting the turbulence development and the associated heating. We consider the combined effects of turbulence and leakage in determining the energy level and associated heating rate in models of coronal loops which include the chromosphere and transition region. We use a piece-wise constant model for the Alfven speed and a Reduced MHD - Shell model to describe the interplay between turbulent dynamics in the direction perpendicular to the mean field and propagation along the field. Turbulence is sustained by incoming fluctuations which are equivalent, in the line-tied case, to forcing by the photospheric shear flows. While varying the turbulence strength, we compare systematically the average coronal energy level (E) and dissipation rate (D) in three models with increasing complexity: the classical closed model, the semi-open corona model, and the corona-chromosphere (or 3-layer) model, the latter two models allowing energy leakage. We find that: (i) Leakage always plays a role (even for strong turbulence), E and D are systematically lower than in the line-tied model. (ii) E is close to the resonant prediction, i.e., assuming effective turbulent correlation time longer than the Alfven coronal crossing time (Ta). (iii) D is close to the value given by the ratio of photospheric energy divided by Ta (iv) The coronal spectra exibits an inertial range with 5/3 spectral slope, and a large scale peak of trapped resonant modes that inhibit nonlinear couplings. (v) In the realistic 3-layer model, the two-component spectrum leads to a damping time equal to the Kolmogorov time reduced by a factor u_rms/Va_coronaComment: 15 pages, 15 figures, Accepted for publication in A&

Modelling 3D scene based on rapid face tracking and objects recognition

Mixed reality techniques are presented. Implementation and application of CAMSHIFT algorithm is discussed to some extent. In the initial stage of the research the technology of real object's edge detection and geometrical figures' representation in the virtual scene has been worked out

A turbulence-driven model for heating and acceleration of the fast wind in coronal holes

A model is presented for generation of fast solar wind in coronal holes, relying on heating that is dominated by turbulent dissipation of MHD fluctuations transported upwards in the solar atmosphere. Scale-separated transport equations include large-scale fields, transverse Alfvenic fluctuations, and a small compressive dissipation due to parallel shears near the transition region. The model accounts for proton temperature, density, wind speed, and fluctuation amplitude as observed in remote sensing and in situ satellite data.Comment: accepted for publication in ApJ

STUDY OF SI SURFACE MODIFICATION WITH IRRADIATION, PLASMA AND ULTRASOUND FOR GAS SENSING APPLICATION

In order to search the new physical principles for high sensitive and selective gas sensors on the base of porous silicon creating we examined gas sensitivity of the silicon surface modified with charge particle irradiation, chemical plasma and ultrasound. Single crystal Si and SiO2/Si structures were irradiated with ions (6.8 MeV H, 27.2 MeV He, 290 MeV Ar, 372 MeV Xe, 710 MeV Bi), treated with chemical plasma with 80-100eV F-content and with ultrasound (Р=0.5 W, 8 MHz). The sample’s absorption properties were obtained from the analysis of the optical parameters changes (refraction index and absorption coefficient, and a thickness of near-surface region, too). The latest were studied by the method of multiangular monochromatic ellipsometry in test camera in ethyl alcohol, ammonia and acetone environment. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to analyze the surface morphology. Protons and alpha particles were found to lead to the Si near-surface layer destruction of and an enhancement of the surface roughness. The proton irradiated samples revealed a higher sensitivity to the absorption of ammonia and acetone molecules. Plasma treated Si displays surface modification (loosening of near-surface layer), though, gas absorption is not clearly revealed. Optical properties of Si/SiO2 structures depend on the dimensions and the depths of nanopores, created by the etching of latent tracks in dioxide after irradiation. The greatest optical constant changes occurred in irradiated with 209Ві structures, where tracks penetrated the whole dioxide. Accordingly bismuth-irradiated structures have the best gas sensitivity. Ultrasound influences on the optical parameters of porous Si/SiO2 structure (loosening of the near-surface layer). However, these changes are unstable; and optical characteristics relax to the initial value in time. The best result was obtained for SnO2 /SiO2 /Si structure, where nanopores etched in the Xe latent tracks areas, were filled with SnO2

Turbulence in the sub-Alfv\'enic solar wind driven by reflection of low-frequency Alfv\'en waves

We study the formation and evolution of a turbulent spectrum of Alfv\'en waves driven by reflection off the solar wind density gradients, starting from the coronal base up to 17 solar radii, well beyond the Alfv\'enic critical point. The background solar wind is assigned and 2D shell models are used to describe nonlinear interactions. We find that the turbulent spectra are influenced by the nature of reflected waves. Close to the base, these give rise to a flatter and steeper spectrum for the outgoing and reflected waves respectively. At higher heliocentric distance both spectra evolve toward an asymptotic Kolmogorov spectrum. The turbulent dissipation is found to account for at least half of the heating required to sustain the background imposed solar wind and its shape is found to be determined by the reflection-determined turbulent heating below 1.5 solar radii. Therefore reflection and reflection-driven turbulence are shown to play a key role in the accelerationof the fast solar wind and origin of the turbulent spectrum found at 0.3 AU in the heliosphere.Comment: Accepted for publication in ApJ

Energization of charged test particles in magnetohydrodynamic fields: waves vs turbulence picture

Direct numerical simulations of 3D compressible MHD turbulence were performed in order to study the relation between waves modes and coherent structures and the consequent energization of test particles. Moreover, the question of which is the main mechanism of this particle energization is rigorously discussed. In particular, using the same initial conditions, we analyzed the non-linear and linear evolution of a turbulent state along with the case of randomized phases. Then, the behavior of the linear and non-linear simulations were compared through the study of time evolution of particle kinetic energy and preferential concentration. Also, spatio temporal spectra were used to identify the presence of wave modes and quantify the fraction of energy around the MHD modes in linear and non-linear simulations. Finally, the variation of the correlation time of the external forcing is studied in detail along with the effect on the particle energization (and clustering) and the presence of wave modes. More specifically, particle energization tends to decrease when the fraction of linear energy increase, supporting the idea that energization by structures is the dominant mechanism for particle energization instead of resonating with wave modes as suggested by Fermi energization theory

Heating of the Solar Chromosphere and Corona by Alfven Wave Turbulence

A three-dimensional MHD model for the propagation and dissipation of Alfven waves in a coronal loop is developed. The model includes the lower atmospheres at the two ends of the loop. The waves originate on small spatial scales (less than 100 km) inside the kilogauss flux elements in the photosphere. The model describes the nonlinear interactions between Alfven waves using the reduced MHD approximation. The increase of Alfven speed with height in the chromosphere and transition region (TR) causes strong wave reflection, which leads to counter-propagating waves and turbulence in the photospheric and chromospheric parts of the flux tube. Part of the wave energy is transmitted through the TR and produces turbulence in the corona. We find that the hot coronal loops typically found in active regions can be explained in terms of Alfven wave turbulence, provided the small-scale footpoint motions have velocities of 1-2 km/s and time scales of 60-200 s. The heating rate per unit volume in the chromosphere is 2 to 3 orders of magnitude larger than that in the corona. We construct a series of models with different values of the model parameters, and find that the coronal heating rate increases with coronal field strength and decreases with loop length. We conclude that coronal loops and the underlying chromosphere may both be heated by Alfvenic turbulence.Comment: 28 pages (emulateapj style, 13 figures, 3 tables), ApJ, in pres