Numerical simulations of conversion to Alfven waves in sunspots

We study the conversion of fast magneto-acoustic waves to Alfven waves by means of 2.5D numerical simulations in a sunspot-like magnetic configuration. A fast, essentially acoustic, wave of a given frequency and wave number is generated below the surface and propagates upward though the Alfven/acoustic equipartition layer where it splits into upgoing slow (acoustic) and fast (magnetic) waves. The fast wave quickly reflects off the steep Alfven speed gradient, but around and above this reflection height it partially converts to Alfven waves, depending on the local relative inclinations of the background magnetic field and the wavevector. To measure the efficiency of this conversion to Alfven waves we calculate acoustic and magnetic energy fluxes. The particular amplitude and phase relations between the magnetic field and velocity oscillations help us to demonstrate that the waves produced are indeed Alfven waves. We find that the conversion to Alfven waves is particularly important for strongly inclined fields like those existing in sunspot penumbrae. Equally important is the magnetic field orientation with respect to the vertical plane of wave propagation, which we refer to as "field azimuth". For field azimuth less than 90 degrees the generated Alfven waves continue upwards, but above 90 degrees downgoing Alfven waves are preferentially produced. This yields negative Alfven energy flux for azimuths between 90 and 180 degrees. Alfven energy fluxes may be comparable to or exceed acoustic fluxes, depending upon geometry, though computational exigencies limit their magnitude in our simulations.Comment: Accepted for publication in Ap

Fast-to-Alfv\'en mode conversion mediated by Hall current. II Application to the solar atmosphere

Coupling between fast magneto-acoustic and Alfv\'en waves can be observe in fully ionized plasmas mediated by stratification and 3D geometrical effects. In Paper I, Cally & Khomenko (2015) have shown that in a weakly ionized plasma, such as the solar photosphere and chromosphere, the Hall current introduces a new coupling mechanism. The present study extends the results from Paper I to the case of warm plasma. We report on numerical experiments where mode transformation is studied using quasi-realistic stratification in thermodynamic parameters resembling the solar atmosphere. This redresses the limitation of the cold plasma approximation assumed in Paper I, in particular allowing the complete process of coupling between fast and slow magneto-acoustic modes and subsequent coupling of the fast mode to the Alfv\'en mode through the Hall current. Our results confirm the efficacy of the mechanism proposed in Paper I for the solar case. We observe that the efficiency of the transformation is a sensitive function of the angle between the wave propagation direction and the magnetic field, and of the wave frequency. The efficiency increases when the field direction and the wave direction are aligned for increasing wave frequencies. After scaling our results to typical solar values, the maximum amplitude of the transformed Alfv\'en waves, for a frequency of 1 Hz, corresponds to an energy flux (measured above the height of peak Hall coupling) of $\sim10^3$ $\rm W\,m^{-2}$, based on an amplitude of 500 $\rm m\,s^{-1}$ at $\beta=1$, which is sufficient to play a major role in both quiet and active region coronal heating

Value-based approach to managing the risks of investing in oil and gas business

Development of the oil and gas business is inextricably linked to large-scale investment programs. Large-scale flow of capital funds, long duration of projects, as well as the external environment's high uncertainty for oil and gas businesses bring about the high-risk investing; and therefore, it becomes urgent to develop methodological tools for risk management issues. The authors' approach to risk management of capital investments allows an individual to estimate the risk level of an investment project on the basis of a ratings model, and to evaluate the need for capital to cover potential losses on the basis of the target level of financial stability and long-term strategy of the company. The authors' technique of RAROC (risk adjusted return on capital) analysis of investment projects allows to calculate the risk-adjusted return on investment and to carry out the selection of projects that contribute most to the creation of value and screen out those projects that destroy the company value. The results can be used by management of oil companies, investors, and analysts in financial decision-making. © 2017 WIT Press

Optimization of financing investments in a power-generation company

Attracting investment in the Russian energy industry is a necessary condition for improving the competitiveness of energy companies. It is important to create an investment budget financing structure, in which the weighted average cost of funds will be minimal, and the amount of resources drawn from each source to fit the current market trends and financial sustainability criteria power generation company. This paper discusses problems of investment financing optimization of a power generation company, a proposed optimization model of investment financing and calculated parameters for the optimization of the investment program in the example of a Russian power generating company. © 2014 WIT Press.International Journal of Safety and Security Engineering;International Journal of Sustainable Development and Planning;WIT Transactions on Ecology and the Environmen

Risk management of mergers and acquisitions with borrowed capital in the energy sector

Under the conditions of macroeconomic instability and the difficulty of forecasting trends in the market development, a competitive recovery of the electric power business is possible only by attracting large capital investment. Mergers and acquisitions deals that make it possible to concentrate assets and to amalgamate the industry business are done through the leveraged buy-out (LBO) scheme. However, LBO deals are associated not only with the investor's risks, but also with the risks of the acquirers and vendors. The article presents the authors' model of risks formalization of LBO deals. It allows for consolidating the blocks of key project and financial indicators, parameters of a specific risk, and macroeconomic and sectoral factors. The developed model yields an indicative assessment of the degree of risk of LBO deals taking into account the industry specifics. A mechanism for determining the position of the creditor in the framework of LBO is proposed as a practical application of this model. The results of the study can be used by the management of energy companies, investors and analysts in making financial decisions. © 2018 WIT Press.The work was supported by act 211 of the government of the Russian federation, contract no 02.a03.21.0006

A risk-oriented approach to capital management at a power generation company in Russia

One of the challenges facing the energy industry today is how to improve investment attractiveness and business competitiveness in energy generation. It is becoming particularly important to enhance the sectoral risk management systems in order to ensure long-term growth and sustainable development in the energy sector amidst numerous factors and uncertainties created by the globalization of the financial markets. This paper presents the authors’ approach to assessing sectoral risks in the energy industry based on capital management for the purpose of achieving a certain level of long-term financial stability. The practicalities of applying the proposed approach to sectoral risk assessment are considered using a power generation company as an example. © 2014 WIT Press

Properties of high-frequency wave power halos around active regions: an analysis of multi-height data from HMI and AIA onboard SDO

We study properties of waves of frequencies above the photospheric acoustic cut-off of $\approx$5.3 mHz, around four active regions, through spatial maps of their power estimated using data from Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO). The wavelength channels 1600 {\AA} and 1700 {\AA} from AIA are now known to capture clear oscillation signals due to helioseismic p modes as well as waves propagating up through to the chromosphere. Here we study in detail, in comparison with HMI Doppler data, properties of the power maps, especially the so called 'acoustic halos' seen around active regions, as a function of wave frequencies, inclination and strength of magnetic field (derived from the vector field observations by HMI) and observation height. We infer possible signatures of (magneto-)acoustic wave refraction from the observation height dependent changes, and hence due to changing magnetic strength and geometry, in the dependences of power maps on the photospheric magnetic quantities. We discuss the implications for theories of p mode absorption and mode conversions by the magnetic field.Comment: 22 pages, 12 figures, Accepted by journal Solar Physic

Signatures of the impact of flare ejected plasma on the photosphere of a sunspot light-bridge

We investigate the properties of a sunspot light-bridge, focusing on the changes produced by the impact of a plasma blob ejected from a C-class flare. We observed a sunspot in active region NOAA 12544 using spectropolarimetric raster maps of the four Fe I lines around 15655 \AA\ with the GREGOR Infrared Spectrograph (GRIS), narrow-band intensity images sampling the Fe I 6173 \AA\ line with the GREGOR Fabry-P\'erot Interferometer (GFPI), and intensity broad band images in G-band and Ca II H band with the High-resolution Fast Imager (HiFI). All these instruments are located at the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The data cover the time before, during, and after the flare event. The analysis is complemented with Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) data from the Solar Dynamics Observatory (SDO). The physical parameters of the atmosphere at differents heights were inferred using spectral-line inversion techniques. We identify photospheric and chromospheric brightenings, heating events, and changes in the Stokes profiles associated to the flare eruption and the subsequent arrival of the plasma blob to the light bridge, after traveling along an active region loop. The measurements suggest that these phenomena are the result of reconnection events driven by the interaction of the plasma blob with the magnetic field topology of the light bridge.Comment: Accepted for publication in A&

An introductory guide to fluid models with anisotropic temperatures Part 1 -- CGL description and collisionless fluid hierarchy

We present a detailed guide to advanced collisionless fluid models that incorporate kinetic effects into the fluid framework, and that are much closer to the collisionless kinetic description than traditional magnetohydrodynamics. Such fluid models are directly applicable to modeling turbulent evolution of a vast array of astrophysical plasmas, such as the solar corona and the solar wind, the interstellar medium, as well as accretion disks and galaxy clusters. The text can be viewed as a detailed guide to Landau fluid models and it is divided into two parts. Part 1 is dedicated to fluid models that are obtained by closing the fluid hierarchy with simple (non Landau fluid) closures. Part 2 is dedicated to Landau fluid closures. Here in Part 1, we discuss the CGL fluid model in great detail, together with fluid models that contain dispersive effects introduced by the Hall term and by the finite Larmor radius (FLR) corrections to the pressure tensor. We consider dispersive effects introduced by the non-gyrotropic heat flux vectors. We investigate the parallel and oblique firehose instability, and show that the non-gyrotropic heat flux strongly influences the maximum growth rate of these instabilities. Furthermore, we discuss fluid models that contain evolution equations for the gyrotropic heat flux fluctuations and that are closed at the 4th-moment level by prescribing a specific form for the distribution function. For the bi-Maxwellian distribution, such a closure is known as the "normal" closure. We also discuss a fluid closure for the bi-kappa distribution. Finally, by considering one-dimensional Maxwellian fluid closures at higher-order moments, we show that such fluid models are always unstable. The last possible non Landau fluid closure is therefore the "normal" closure, and beyond the 4th-order moment, Landau fluid closures are required.Comment: Improved version, accepted to JPP Lecture Notes. Some parts were shortened and some parts were expanded. The text now contains Conclusion