The universally growing mode in the solar atmosphere: coronal heating by drift waves

The heating of the plasma in the solar atmosphere is discussed within both frameworks of fluid and kinetic drift wave theory. We show that the basic ingredient necessary for the heating is the presence of density gradients in the direction perpendicular to the magnetic field vector. Such density gradients are a source of free energy for the excitation of drift waves. We use only well established basic theory, verified experimentally in laboratory plasmas. Two mechanisms of the energy exchange and heating are shown to take place simultaneously: one due to the Landau effect in the direction parallel to the magnetic field, and another one, stochastic heating, in the perpendicular direction. The stochastic heating i) is due to the electrostatic nature of the waves, ii) is more effective on ions than on electrons, iii) acts predominantly in the perpendicular direction, iv) heats heavy ions more efficiently than lighter ions, and v) may easily provide a drift wave heating rate that is orders of magnitude above the value that is presently believed to be sufficient for the coronal heating, i.e., $\simeq 6 \cdot 10^{-5}$J/(m$^3$s) for active regions and $\simeq 8 \cdot 10^{-6}$J/(m$^3$s) for coronal holes. This heating acts naturally through well known effects that are, however, beyond the current standard models and theories.Comment: To appear in MNRA

Solar Wind Turbulence and the Role of Ion Instabilities

International audienc

Numerical modeling of coupled hydrodynamic-chemical-biodegradation processes in coal mine water quality formation and evolution

The formation and evolution mechanisms of coal mine water quality are intricate, significantly influenced by multiple processes such as hydrodynamics, hydrochemistry, and biodegradation. A comprehensive investigation and elucidation of the mechanisms is theoretically crucial for the prevention and remediation of coal mine water pollution. The hydrogeological prototype of a goaf in a coal mine in the Ordos Basin is choosen, and a laboratorial physical model and a coupled hydrodynamic-chemical-biodegradation (HCB) milti-field numerical model for the goaf are established, focusing the water level rises and biogeochemistry processes. The research results demonstrate the significance of multi-field coupling effects on mine water quality. The water level filling up results shows that the matrix-fracture dual-porosity model effectively matches the water level in the goaf with a simulation error of 9.9%, which is much more accurate than the theoretical and the single-porosity model predictions. The simulation results of the hydrochemical field are relatively consistent with the experiments, with relative errors of 3.0%, 21.0%, and 6.2% for \begin{document}${\mathrm{SO}}_4^{2-}$\end{document}, \begin{document}${\mathrm{HCO}}_3^-$\end{document}, and pH, respectively. Results from different time periods indicate that water-rock reactions and microbial activities are not significant during the water storage process. After the goaf is filled up, the hydrodynamics almost stagnate, but the hydrochemical and microbial fields are relatively active. The pyrite oxidation reactions in the No.2 and No.3 coal seams increase the concentration of \begin{document}${\mathrm{SO}}_4^{2-}$\end{document} by about 24.6%. In the later stage, the water environment in the goaf evolves into weakly acidic and anaerobic reducing conditions, and the microbial degradation becomes prominent, reducing the \begin{document}${\mathrm{SO}}_4^{2-}$\end{document} concentration from its peak by 6.1%. A certain “self-purification” ability of mine water in the goaf after closure has been confirmed. By adjusting the microbial metabolic rate constant, the proportion of \begin{document}${\mathrm{SO}}_4^{2-}$\end{document} degradation can be induced up to 61.6%. In actual engineering scenarios, this target can be achieved through some strategies such as supplementing enough dissolved carbon nutrient substance and artificially establishing a closed anaerobic environment. This study expands the multi-field coupling laboratorial experiments and numerical modeling techniques to the formation and evolution of water quality in coal mine water in a goaf, and the constructive conclusions can provide theoretical guidance for the prevention and remediation of coal mine water pollution

Deep Groundwater Flow Patterns Induced by Mine Water Injection Activity

Mine water injection into deep formations is one of the effective approaches for reducing the drainage from coal mines in the arid and semi-arid region of the Ordos basin, China. Many coal mines are attempting to execute the related projects. Under the influence of groundwater protection, the understanding of regional groundwater flow is becoming highly important to the mine water monitoring, whereas quite few academic research teams focus on the deep groundwater flow pattern by mine water injection. This paper reveals the spatial distribution of Liujiagou Formation that is in positive correlation with the terrain, and its local thickness is influenced by the dominant W-E and NE-SW directions of geological structures. Only a part of sandstone rocks consists of aquifers, the rest 61.9% of relatively dry rock provide the enhanced storage space and partial mudstone aquicludes decrease the possibility of the vertical leakage for mine water. The dynamic storage capacity is evaluated at 2.36 Mm3 per 1 km2 and over 25.10 billion m3 in this study area. Two hydrogeologic cross-sections of basin-scale identify the W-E and N-S regional groundwater flow directions, with the lower Yellow River catchment becoming the discharged region. The hierarchically and steadily nested flow systems containing coal mining claims are influenced by coal mining activity. The groundwater depression cone in a shallow coal measure aquifer is caused by mine water drainage whereas the groundwater mound in Liujiagou Formation is generated by mine water injection activity. The numerical simulation revealed that the groundwater head rebound is slightly decreased and will not recover to its initial baseline within 500 years due to its low porosity and permeability. This study elucidates the deep groundwater flow patterns induced by mine water injection and provides a practical methodology for the management and pollution monitoring of mine water injection activity