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This paper outlines the initial development of a novel magnetohydrodynamic (MHD) plasma control sys- tem which aims at mitigating shock-induced heating and the radio-frequency communication blackout typically encountered during (re-)entry into planetary atmospheres. An international consortium com- prising universities, SMEs, research institutions, and industry has been formed in order to develop this technology within the MEESST project. The latter is funded by the Future and Emerging Technologies (FET) program of the European Commission’s Horizon 2020 scheme (grant no. 899298). Atmospheric en- try imposes one of the harshest environments which a spacecraft can experience. The combination of hypersonic velocities and the rapid compression of atmospheric particles by the spacecraft leads to high- enthalpy, partially ionised gases forming around the vehicle. This inhibits radio communications and in- duces high thermal loads on the spacecraft surface. For the former problem, spacecraft can sometimes rely on satellite constellations for communicating through the plasma wake and therefore preventing the blackout. On the other hand, expensive, heavy, and non-reusable thermal protection systems (TPS) are needed to dissipate the severe thermal loads. Such TPS can represent up to 30% of an entry vehicles weight, and especially for manned missions they can reduce the cost- efficiency by sacrificing payload mass. Such systems are also prone to failure, putting the lives of astronauts at risk. The use of electro- magnetic fields to exploit MHD principles has long been considered as an attractive solution for tackling the problems described above. By pushing the boundary layer of the ionized gas layer away from the spacecraft, the thermal loads can be reduced, while also opening a magnetic window for radio com- munications and mitigating the blackout phenomenon. The application of this MHD-enabled system has previously not been demonstrated in realistic conditions due to the required large magnetic fields (on the order of Tesla or more), which for conventional technologies would demand exceptionally heavy and power-hungry electromagnets. High-temperature superconductors (HTS) have reached a level of industrial maturity sufficient for them to act as a key enabling technology for this application. Thanks to superior current densities, HTS coils can offer the necessary low weight and compactness required for space ap- plications, with the ability to generate the strong magnetic fields needed for entry purposes. This paper provides an overview of the MEESST project, including its goals, methodology and some preliminary de- sign considerations. ispartof: The Journal of Space Safety Engineering vol:10 issue:1 pages:27-34 status: published

Context. Solar coronal mass ejections (CMEs) can catch up and interact with preceding CMEs and solar wind structures to undergo rotation and deflection during their propagation. Aim. We aim to show how the interactions of a CME in the corona and heliosphere can play a significant role in altering its geoeffectiveness as predicted at the time of its eruption. To do so, we consider a case study of two successive CMEs launched from the active region NOAA 12158 in early September 2014. The second CME was predicted to be extensively geoeffective based on the remote-sensing observations of the source region. However, in situ measurements at 1 au recorded only a short-lasting, weak negative Bz component followed by a prolonged positive Bz component. Methods. We used the EUropean Heliosphere FORecasting Information Asset (EUHFORIA) to perform a self-consistent 3D magnetohydrodynamical (MHD) data-driven simulation of the two CMEs in the heliosphere. First, the ambient solar wind is modelled, followed by the time-dependent injection of CME1 with the LFF spheromak and CME2 with the Flux Rope in 3D (FRi3D) model. The initial conditions of the CMEs are determined by combining observational insights near the Sun, which are fine-tuned to match the in situ observations near 1 au, with additional numerical experiments related to each individual CME. Results. By introducing CME1 before CME2 in the EUHFORIA simulation, we modelled the negative Bz component in the sheath region ahead of CME2 whose formation can be attributed to the interaction between CME1 and CME2. To reproduce the positive Bz component in the magnetic ejecta of CME2, we had to initialise CME2 with an orientation determined at 0.1 au and consistent with the orientation interpreted at 1 au instead of the orientation observed during its eruption. Conclusions. EUHFORIA simulations suggest the possibility of a significant rotation of CME2 in the low corona in order to explain the in situ observations at 1 au. Coherent magnetic field rotations with enhanced strength (potentially geoeffective) can be formed in the sheath region as a result of interactions between two CMEs in the heliosphere even if the individual CMEs are not geoeffective. ispartof: Astronomy & Astrophysics vol:675 status: accepted

During the atmospheric entry phase at hypersonic speed, the radio communication from/to a space vehicle can be disrupted due to the formation of a plasma sheath within the surrounding flow field. In order to characterize such communication blackout phases, this work presents a numerical methodology combining Computational Fluid Dynamic (CFD) simulations of ionized chemically reacting entry flows by means of Computational Object-Oriented Libraries for Fluid Dynamics (COOLFluiD) and a ray tracing analysis by means of the newly developed BlackOut RAy Tracer (BORAT). The latter is based on the numerical solution of the 3D Eikonal system of equations, offering a fast, efficient and accurate method to analyse the interaction between electromagnetic signals and weakly ionised plasmas. The proposed methodology, and BORAT in particular, is first verified on popular benchmark cases and then used to analyse the European Space Agency (ESA) 2016 ExoMars Schiaparelli entry flight into Martian environment. The corresponding results demonstrate the validity of the proposed ray tracing approach for predicting communication blackout, where signals emitted from the on-board antenna undergo reflection and refraction from the plasma surrounding the entry vehicle, and the advantage of a 3D approach for analysing real flight configuration. ispartof: Computer Physics Communications vol:286 status: published

The propagation of Interplanetary Coronal Mass Ejections (ICMEs) in the heliosphere is influenced by many physical phenomena, related to the internal structure of the ICME and its interaction with the ambient solar wind and magnetic field. As the solar magnetic field is modulated by the 11-year dynamo cycle, our goal is to perform a theoretical exploratory study to assess the difference of propagation of an ICME in typical minimum and maximum activity backgrounds. We define a median representative CME at 0.1~au, using both observations and numerical simulations, and describe it using a spheromak model. We use the heliospheric propagator European Heliospheric FORecasting Information Asset (EUHFORIA) to inject the same ICME in two different background wind environments. We then study how the environment and the internal CME structure impact the propagation of the ICME towards Earth, by comparison with an unmagnetized CME. At minimum of activity, the structure of the heliosphere around the ecliptic causes the ICME to slow down, creating a delay with the polar parts of the ejecta. This delay is more important if the ICME is faster. At maximum of activity, a southern coronal hole causes a northward deflection. For these cases, we always find that the ICME at maximum of activity arrives first, while the ICME at minimum of activity is actually more geo-effective. The helicity sign of the ICME is also a crucial parameter but at minimum of activity only, since it affects the magnetic profile and the arrival time of up to 8 hours., Comment: 25 pages, 16 figures, accepted in ApJ

We present simulation results of a gradual solar energetic particle (SEP) event detected on 2021 October 9 by multiple spacecraft, including BepiColombo (Bepi) and near-Earth spacecraft such as the Advanced Composition Explorer (ACE). A peculiarity of this event is that the presence of a high speed stream (HSS) affected the low-energy ion component ($\lesssim 5$ MeV) of the gradual SEP event at both Bepi and ACE, despite the HSS having only a modest solar wind speed increase. Using the EUHFORIA (European Heliospheric FORecasting Information Asset) magnetohydrodynamic model, we replicate the solar wind during the event and the coronal mass ejection (CME) that generated it. We then combine these results with the energetic particle transport model PARADISE (PArticle Radiation Asset Directed at Interplanetary Space Exploration). We find that the structure of the CME-driven shock was affected by the non-uniform solar wind, especially near the HSS, resulting in a shock wavefront with strong variations in its properties such as its compression ratio and obliquity. By scaling the emission of energetic particles from the shock to the solar wind compression at the shock, an excellent match between the PARADISE simulation and in-situ measurements of $\lesssim 5$ MeV ions is obtained. Our modelling shows that the intricate intensity variations observed at both ACE and Bepi were influenced by the non-uniform emission of energetic particles from the deformed shock wave and demonstrates the influence of even modest background solar wind structures on the development of SEP events., Comment: 13 pages, 7 figures, accepted for publication in The Astrophysical Journal

Investigating the early-stage evolution of an erupting flux rope from the Sun is important to understand the mechanisms of how it looses its stability and its space weather impacts. Our aim is to develop an efficient scheme for tracking the early dynamics of erupting solar flux ropes and use the algorithm to analyse its early-stage properties. The algorithm is tested on a data-driven simulation of an eruption that took place in active region AR12473. We investigate the modelled flux rope's footpoint movement and magnetic flux evolution and compare with observational data from the Solar Dynamics Observatory's Atmospheric Imaging Assembly in the 211 $\unicode{x212B}$ and 1600 $\unicode{x212B}$ channels. To carry out our analysis, we use the time-dependent data-driven magnetofrictional model (TMFM). We also perform another modelling run, where we stop the driving of the TMFM midway through the flux rope's rise through the simulation domain and evolve it instead with a zero-beta magnetohydrodynamic (MHD) approach. The developed algorithm successfully extracts a flux rope and its ascend through the simulation domain. We find that the movement of the modelled flux rope footpoints showcases similar trends in both TMFM and relaxation MHD run: they recede from their respective central location as the eruption progresses and the positive polarity footpoint region exhibits a more dynamic behaviour. The ultraviolet brightenings and extreme ultraviolet dimmings agree well with the models in terms of their dynamics. According to our modelling results, the toroidal magnetic flux in the flux rope first rises and then decreases. In our observational analysis, we capture the descending phase of toroidal flux. In conclusion, the extraction algorithm enables us to effectively study the flux rope's early dynamics and derive some of its key properties such as footpoint movement and toroidal magnetic flux., Comment: Accepted for publication in Astronomy & Astrophysics

We developed COolfluid COroNa UnsTructured (COCONUT) - a novel global coronal model based on the COOLFluiD numerical code. The steady-state solution is determined by the inner boundary defined by magnetogram data in combination with fixed hydrodynamic values representative of the typical corona, while inside the numerical domain of our simulation, the corona is described by the set of ideal-MHD equations with gravity. The latter is solved with use of an implicit solver on an unstructured grid. Our code has passed a set of benchmark tests and proved its accuracy for simple dipole / quadrupole solutions as well as for a wide range of magnetograms, both during solar minima and solar maxima. With various numerical optimization techniques and an adaptive CFL step, we decreased the computation time while maintaining the high robustness and reliability. Finally, we coupled the obtained results with the heliospheric wind model of EUHFORIA 2.0 space weather forecast to show its forecast abilities. All this leads to an accurate MHD solution obtained within only a few hours of computation, which is crucial for space weather forecast systems. Here we present some of the numerically obtained results for selected magnetograms chosen to represent a variety of stages of the solar activity, from minimum to maximum, with each of them corresponding to a particular solar eclipse, to allow us the direct comparison of simulations with the observed coronal structures. Following the commonly used procedure, the input raw / original MDI and HMI magnetograms are pre-processed by projection on spherical harmonics and a selection of a maximum frequency for the reconstruction. This is equivalent to a smoothing of the map and results in removal of the small, intense magnetic structures on the solar surface. These are in fact numerically more challenging to capture, while their contribution to the overall structure of the solar wind at 0.1 AU and the largescale coronal magnetic fields has not been thoroughly investigated yet. With several maps and several levels of accuracy of reconstruction we address this problem and show the map resolution and pre-processing impact on accuracy of the numerical results. This is especially important for computationally challenging maximum-activity magnetograms which require significant pre-processing for stability and satisfactory computational speed. To verify our numerical results, we use a validation scheme proposed by Wagner et al. 2022 (from less to more sophisticated methods, i.e., visual classification, feature matching, streamer direction and width, brute force matching, topology classification). We investigate the distribution of magnetic structures as predicted by our simulations and compare them to the obtained coronal magnetic field topology. The detailed comparison with observations reveals that our model recreates relevant features such as the position and the shape of the streamers (by comparison with white-light images), the coronal holes (by comparison with EUV images) and the current sheet (by comparison with WSA model at 0.1 AU). We conclude that an unprecedented combination of accuracy, computation speed and robustness is accomplished at this stage, with possible improvements in the foreseeable future, such as inclusion of more physics or implementation of the adaptive mesh refinement technique. Our results also show that the final solution is still very sensitive to the map chosen and its pre-processing, especially for solar maximum-activity cases OPRN ACCESS: https://amostech.com/TechnicalPapers/2022/Poster/Kuzma.pdf ispartof: pages:1622-1628 ispartof: AMOS 2022 conference proceedings vol:2022 pages:1622-1628 ispartof: 23rd AMOS Conference 2022 location:Maui, Hawai'i, USA date:27 Sep - 30 Sep 2022 status: published

The present paper will address the development and implementation of the high-order Flux Reconstruction (FR) schemes for high-speed flows on both straight and curved edged simplex elements within the open-source COOLFluiD (Computational Object-Oriented Libraries for Fluid Dynamics) platform. While the FR method potentially provides a more accurate detection of complex flow features over relatively coarser mesh, when compared to their low-order peers, the approach suffers from the same pacing items as the other high-order methods such as the slow convergence to steady state and the lack of robust shock capturing capabilities. To overcome such deficiencies, Adaptive Mesh Refinement (AMR) represent a robust procedure for improving the quality of the physical results, especially shock capturing capabilities, due to a local increase of the grid resolution and mesh/shock alignment. Particularly, spring-based and physics-driven rrefinement (r-AMR) requires a compact stencil and is suitable for parallel computing. This fact goes hand in hand with the FR method since the latter can obtain arbitrary high orders of accuracy without requiring a wide stencil at higher orders. In this work, a concise overview of the FR method and spring-based AMR techniques will be given, followed by some promising results of subsonic flow simulations using FR in simplex elements and r-AMR-FR applied to benchmark high-order supersonic test cases. ispartof: pages:1-25 ispartof: ICCFD11 PROCEEDINGS vol:https://www.iccfd.org/iccfd11/proceedings.html pages:1-25 ispartof: Eleventh International Conference on Computational Fluid Dynamics (ICCFD11) location:Maui, Hawaii, USA date:11 Jul - 15 Jul 2022 status: published

This works presents the development of a three-dimensional solver for the numerical analysis of the communication blackout encountered in atmospheric entry flights. The proposed methodology is based on computational fluid dynamic (CFD) simulation in combination with a ray tracing numerical technique. The ray tracing algorithm is based on the implementation of the Eikonal system of equation, a fast, efficient and accurate method to analyse interaction of electromagnetic signals and weakly ionised plasmas. The proposed methodology is applied to the atmospheric entry of the ExoMars capsule in Martian environemnt and shows the capability of a three-dimensional approach to analyse real flight configuration. Results demonstrate the validity of the proposed ray tracing approach for the analysis of communication blackout, where signals emitted from the on-board antenna undergo reflection and refraction from the plasma surrounding the entry vehicle. ispartof: pages:1-13 ispartof: ICCFD11 PROCEEDINGS vol:https://www.iccfd.org/iccfd11/proceedings.html pages:1-13 ispartof: Eleventh International Conference on Computational Fluid Dynamics (ICCFD11) location:Maui, HI, USA date:11 Jul - 15 Jul 2022 status: published

This paper studies ICMEs detected by both Voyager spacecraft during propagation from 1 to 10 AU, with observations from 1977 to 1980. ICMEs are detected by using several signatures in the in-situ data, the primary one being the low measured to expected proton temperature ratio. We found 21 events common to both spacecraft and study their internal structure in terms of plasma and magnetic field properties. We find that ICMEs are expanding as they propagate outwards, with decreasing density and magnetic field intensities, in agreement with previous studies. We first carry out a statistical study and then a detailed analysis of each case. Furthermore, we analyse one case in which a shock can be clearly detected by both spacecraft. The methods described here can be interesting for other studies combining data sets from heliospheric missions. Furthermore, they highlight the importance of exploiting useful data from past missions., Comment: 38 pages

In the present paper an analysis of the polarization properties of the solar decameter spikes is performed. We found that decameter spikes can possess both left and right circular polarization which changes from 0 up to 100% with an average value 50%. ispartof: pages:40-43 ispartof: Proceedings of Eleventh Workshop “Solar Influences on the Magnetosphere, Ionosphere and Atmosphere” pages:40-43 ispartof: Eleventh Workshop “Solar Influences on the Magnetosphere, IonoIsphere and Atmosphere” location:Primorsko, Bulgaria date:3 Jun - 7 Jun 2019 status: published

In order to address the growing need for more accurate space-weather predictions, a new model named EUHFORIA (EUropean Heliospheric FORecasting Information Asset) was recently developed. We present the first results of the performance assessment for the solar-wind modeling with EUHFORIA and identify possible limitations of its present setup. Using the basic EUHFORIA 1.0.4 model setup with the default input parameters, we modeled background solar wind (no coronal mass ejections) and compared the obtained results with Advanced Composition Explorer (ACE) in-situ measurements. For the purposes of statistical study we developed a technique of combining daily EUHFORIA runs into continuous time series. The combined time series were derived for the years 2008 (low solar activity) and 2012 (high solar activity), from which in-situ speed and density profiles were extracted. We find for the low-activity phase a better match between model results and observations compared to the high-activity time interval considered. The quality of the modeled solarwind parameters is found to be rather variable. Therefore, to better understand the results obtained we also qualitatively inspected characteristics of coronal holes, i.e. the sources of the studied fast streams. We discuss how different characteristics of the coronal holes and input parameters to EUHFORIA influence the modeled fast solar wind, and suggest possibilities for the improvement of the model. ispartof: Solar Physics vol:294 issue:12 ispartof: location:Netherlands status: published

As is well known, CME propagation often results in the fragmentation of the solar atmosphere on smaller regions of density (magnetic field) enhancement (depletion). It is expected that this type of fragmentation may have radio signatures.}{The general aim of the present paper is to perform a comparative analysis of type III solar and narrow-band type-III-like radio burst properties before and during CME events, respectively. The main goal is to analyze radio observational signatures of the dynamical processes in solar corona. In particular, we aim to perform a comparison of local plasma parameters without and with CME propagation, based on the analysis of decameter radio emission data.}{In order to examine this intuitive expectation, we performed a comparison of usual type III bursts before the CME with narrow-band type-III-like bursts, which are observationally detectable on top of the background type IV radio bursts associated with CME propagation. We focused on the analysis of in total 429 type III and 129 narrow-band type-III-like bursts. We studied their main characteristic parameters such as frequency drift rate, duration, and instantaneous frequency bandwidth using standard statistical methods. Furthermore, we inferred local plasma parameters (e.g.,\ density scale height, emission source radial sizes) using known definitions of frequency drift, duration, and instantaneous frequency bandwidth.}{The analysis reveals that the physical parameters of coronal plasma before CMEs considerably differ from those during the propagation of CMEs (the observational periods 2 and 4 with type IV radio bursts associated with CMEs). Local density radial profiles and the characteristic spatial scales of radio emission sources vary with radial distance more drastically during the CME propagation compared to the cases of quasistatic solar atmosphere without CME(s) (observational periods 1 and 3).}{The results of the work enable us to distinguish different regimes of plasma state in the solar corona. Our results create a solid perspective from which to develop novel tools for coronal plasma studies using radio dynamic spectra. ispartof: Astronomy & Astrophysics vol:625 pages:1-10 status: published

Aims. We introduce a new solar energetic particle (SEP) transport code that aims at studying the effects of different background solar wind configurations on SEP events. In this work, we focus on the influence of varying solar wind velocities on the adiabatic energy changes of SEPs and study how a non-Parker background solar wind can trap particles temporarily at small heliocentric radial distances (≲1.5 AU) thereby influencing the cross-field diffusion of SEPs in the interplanetary space. Methods. Our particle transport code computes particle distributions in the heliosphere by solving the focused transport equation (FTE) in a stochastic manner. Particles are propagated in a solar wind generated by the newly developed data-driven heliospheric model, EUHFORIA. In this work, we solve the FTE, including all solar wind effects, cross-field diffusion, and magnetic-field gradient and curvature drifts. As initial conditions, we assume a delta injection of 4 MeV protons, spread uniformly over a selected region at the inner boundary of the model. To verify the model, we first propagate particles in nominal undisturbed fast and slow solar winds. Thereafter, we simulate and analyse the propagation of particles in a solar wind containing a corotating interaction region (CIR). We study the particle intensities and anisotropies measured by a fleet of virtual observers located at different positions in the heliosphere, as well as the global distribution of particles in interplanetary space. Results. The differential intensity-time profiles obtained in the simulations using the nominal Parker solar wind solutions illustrate the considerable adiabatic deceleration undergone by SEPs, especially when propagating in a fast solar wind. In the case of the solar wind containing a CIR, we observe that particles adiabatically accelerate when propagating in the compression waves bounding the CIR at small radial distances. In addition, for r ≳ 1.5 AU, there are particles accelerated by the reverse shock as indicated by, for example, the anisotropies and pitch-angle distributions of the particles. Moreover, a decrease in high-energy particles at the stream interface (SI) inside the CIR is observed. The compression/shock waves and the magnetic configuration near the SI may also act as a magnetic mirror, producing long-lasting high intensities at small radial distances. We also illustrate how the efficiency of the cross-field diffusion in spreading particles in the heliosphere is enhanced due to compressed magnetic fields. Finally, the inclusion of cross-field diffusion enables some particles to cross both the forward compression wave at small radial distances and the forward shock at larger radial distances. This results in the formation of an accelerated particle population centred on the forward shock, despite the lack of magnetic connection between the particle injection region and this shock wave. Particles injected in the fast solar wind stream cannot reach the forward shock since the SI acts as a diffusion barrier. ispartof: Astronomy & Astrophysics vol:622 status: published

The evolution of the magnetic field and plasma quantities inside a coronal mass ejection (CME) with distance are known from statistical studies using data from 1 au monitors, planetary missions, Helios, and Ulysses. This does not cover the innermost heliosphere, below 0.29 au, where no data are yet publicly available. Here, we describe the evolution of the properties of simulated CMEs in the inner heliosphere using two different initiation mechanisms. We compare the radial evolution of these properties with that found from statistical studies based on observations in the inner heliosphere by Helios and MESSENGER. We find that the evolution of the radial size and magnetic field strength is nearly indistinguishable for twisted flux rope from that of writhed CMEs. The evolution of these properties is also consistent with past studies, primarily with recent statistical studies using in situ measurements and with studies using remote observations of CMEs., Comment: Accepted to APJ. * pages, 6 figures

ispartof: Schriften des Forschungszentrums Julich, Reihe Energie & Umwelt / Energy & Environment vol:xxx ispartof: 13th Carolus Magnus Summer School on Plasma Physics location:resort `Weerterbergen' near Eindhoven (The Netherlands) date:3 Sep - 14 Sep 2018 status: accepted

On 2010 August 14, a wide-angled coronal mass ejection (CME) was observed. This solar eruption originated from a destabilized filament that connected two active regions and the unwinding of this filament gave the eruption an untwisting motion that drew the attention of many observers. In addition to the erupting filament and the associated CME, several other low-coronal signatures that typically indicate the occurrence of a solar eruption were associated to this event. However, contrary to what is expected, the fast CME ($\mathrm{v}>900~\mathrm{km}~\mathrm{s}^{-1}$) was accompanied by only a weak C4.4 flare. We investigate the various eruption signatures that were observed for this event and focus on the kinematic evolution of the filament in order to determine its eruption mechanism. Had this solar eruption occurred just a few days earlier, it could have been a significant event for space weather. The risk to underestimate the strength of this eruption based solely on the C4.4 flare illustrates the need to include all eruption signatures in event analyses in order to obtain a complete picture of a solar eruption and assess its possible space weather impact.

© 2017 URSI. The paper is devoted to the analysis of the unusual event observed on 14 June 2012 in the frequency range 8-42 MHz. During this event the radiation flux changed stepwise two times. Assuming that these changes of radiation flux could be associated with the changes of the coronal plasma parameters (temperature, magnetic field) and using spikes as a tool for the determination of those parameters we traced how the temperature and magnetic field varied during the time of observations. According to the model proposed in the paper the magnetic field was about 1.9 G and the temperature varied in the range of 0.1-0.6 × 106 K at the heights 1.6-3.3 solar radii. ispartof: pages:119-123 ispartof: Sun and Geosphere vol:12 issue:2 pages:119-123 ispartof: 32nd URSI GASS location:Montreal date:19 Aug - 26 Aug 2017 status: published

We study wave properties and instabilities in a magnetized, anisotropic, collisionless plasma in the fluid approximation using the 16-momentum formalism. In particular, we investigated equations different from the ideal MHD equations by including evolution equations for the heat fluxes with different components along the magnetic field _∥ and in the transverse direction _⊥. In this work, we studied the Kelvin-Helmholtz instability that occurs in the contact discontinuity interactions of the slow (350–400 km/s), fast (600–850 km/s) and CME (900–1200 km/s) components of solar wind, taking into account the pressure anisotropic properties ( _⊥, _∥) of the wind plasma. This instability is investigated by solving the 16-momentum set of equations based on an assumed geometry. ispartof: pages:133-136 ispartof: Solar and solar-terrestrial physics 2016 pages:133-136 ispartof: Solar and solar-terrestrial physics 2016, 20th yearly Russian conference on Solar Physics location:Pulkovo (St. Petersburg), Russia date:10 Oct - 14 Oct 2016 status: published

ispartof: Azerbaijani Astronomical Journal vol:11 issue:1 pages:15-19 status: published

We present a computational model for the Earth's magnetosphere that relies on the multi- uid plasma model. When the multi- uid equations are coupled to the full Maxwell's equations, the resulting system is able to tackle non-equilibrium e ects that are beyond the magnetohydrodynamics (MHD) description. The multi- uid model allows for studying relevant phenomena in the Earth's magnetosphere such as the presence of heavier ions, high frequency waves, small scale dynamics, non-thermal equilibrium or separation of the species motion. In this article, the derivation of the multi- uid model from kinetic theory is presented. The propagation of linear waves in the ideal collisionless two- uid model under solar wind and magnetospheric conditions is studied. The two- uid model is implemented using a second order nite volume method. The algorithm is benchmarked against three cases: electromagnetic shock-tube problem, a supersonic plasma ow over a cylinder and over a sphere. The magnetic reconnection occurring in the magnetotail is studied standalone using a two- uid model. Preliminary results of a two- uid global magnetosperic simulation are presented. ispartof: pages:1-1 status: published

ispartof: pages:664-667 ispartof: Proc. 37th EPS Conf. Plasma Phys. vol:1 pages:664-667 ispartof: EPS Conf. Plasma Phys. location:Dublin date:21 Jun - 25 Jun 2010 status: published

In a recent paper [Y. Taroyan, Phys. Rev. Lett 101, 245001 (2008) it is claimed that a new MHD instability of the Alfven wave has been found: incompressible Alfven modes propagating in a compressible spatially varying flow were apparently exponentially amplified. We show that the results of the work follow from an impossible equilibrium and therefore should be disregarded.

ispartof: Frontiers Research Topics nrpages: 91 status: published

Ideal magnetohydrodynamics (MHD) simulations are known to have problems in satisfying the solenoidal constraint (i.e. the divergence of magnetic field should be equal to zero, $ ablacdotvec{B} = 0$). The simulations become unstable unless specific measures have been taken. In this thesis, a solenoidal constraint satisfying technique that allows discrete satisfaction of the solenoidal constraint up to the machine accuracy is presented and validated with a variety of test cases. Due to its inspiration from Chorin's artificial compressibility method developed for incompressible CFD applications, the technique was named as extit{artificial compressibility analogy (ACA)} approach. It is demonstrated that ACA is a purely hyperbolic, stable and consistent technique, which is moreover easy to implement. Unlike some other techniques, it does not pose any problems of the sort that $ ablacdotvec{B}$ errors accumulate in the vicinity of the stagnant regions of flow. With these crucial properties, ACA is thought to be a remedy to the drawbacks of the most commonly used solenoidal constraint satisfying techniques in the literature namely: Incorrect shock capturing and poor performance of the convective stabilization mechanism in regions of stagnant flow for Powell's source term method; exceedingly complex implementation for constrained transport technique due to the staggered grid representation; computationally expensive nature due to the necessity of a Poisson solver combined with hyperbolic/elliptic numerical methods for classical projection schemes. In the first chapter of the thesis, general background knowledge is given about plasmas, MHD and its history, a certain class of upwind finite volume methods, namely Riemann solvers, and their applications in MHD, the definition, constituents, formation mechanisms and effects of space weather and some of the space missions that are and will be performed in its prediction. Secondly, detailed analysis of the compressible ideal MHD equations is given in the form of the derivation of the equations, their dimensionless numbers which will be of use to specify the flows in the following chapters, and finally, the presentation of the MHD waves and discontinuities, which indicates the complexity of the system of ideal MHD equations and therefore their further numerical analysis. The next discussion is about the main subject of the thesis, namely the solenoidal constraint satisfying techniques. First of all, the definition and significance of the solenoidal constraint is given. Afterwards, the most common solenoidal constraint satisfying techniques in the literature are reviewed along with their abovementioned drawbacks. Moreover, particular emphasis is given to the Powell's source term approach which was also implemented in the upwind finite volume MHD solver developed. In addition, the hyperbolic divergence cleaning technique is presented in detail together with the resemblance and differences between it and ACA. Some other solenoidal constraint satisfying techniques are briefly mentioned at this stage. After these, ACA is presented in the following way: The point of inspiration, which is the analogy made with Chorin's artificial compressibility method developed for incompressible CFD, the introduction of the modified system of ideal MHD equations due to ACA, the derivation of the wave equation governing the propagation of $ ablacdotvec{B}$ errors and the analytical consistency proof. Having finished the core discussion of the thesis, the solver developed and its constituents are given in the fourth chapter. Furthermore, a brief overview of the platform into which this solver was implemented, namely COOLFluiD, is also given at this point. Afterwards, a thorough numerical verification of the ACA approach has been made on an increasingly complex suite of test cases. The results obtained with ACA and Powell's source term implementations are given in order to numerically analyse and verify ACA and compare the two methods and validate them with the results from literature. The sixth chapter is devoted to further validation of ACA performed with a variety of more advanced space weather-related simulations. In this chapter, also the $vec{B}_{ extrm{0}} + vec{B}_{ extrm{1}}$ splitting technique used to treat planetary magnetosphere is presented along with its application to ACA and Powell's source term approaches. This technique is utilized in obtaining the solar wind/Earth's magnetosphere interaction results and is based on suppressing the direct inclusion of the Earth's magnetic field, which is a dipole field, in the solution variables. In this way, problems are avoided with the energy equation that could arise from the drastic change of the ratio of the dipole field and the variable field computed by the solver (i.e. $frac{lvertvec{B}_{ extrm{0}}lvert}{lvertvec{B}_{ extrm{1}}lvert}$) in the computational domain. Finally, conclusions and future perspectives related to the material presented in the thesis are put forward., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/published