Author name code: regnier ADS astronomy entries on 2022-09-14 author:"Regnier, Stephane" ------------------------------------------------------------------------ Title: The Independence of Oscillatory Reconnection Periodicity from the Initial Pulse Authors: Karampelas, Konstantinos; McLaughlin, James A.; Botha, Gert J. J.; Régnier, Stéphane Bibcode: 2022ApJ...933..142K Altcode: 2022arXiv220701980K Oscillatory reconnection can manifest through the interaction between the ubiquitous MHD waves and omnipresent null points in the solar atmosphere and is characterized by an inherent periodicity. In the current study, we focus on the relationship between the period of oscillatory reconnection and the strength of the wave pulse initially perturbing the null point, in a hot coronal plasma. We use the PLUTO code to solve the fully compressive, resistive MHD equations for a 2D magnetic X-point. Using wave pulses with a wide range of amplitudes, we perform a parameter study to obtain values for the period, considering the presence and absence of anisotropic thermal conduction separately. In both cases, we find that the resulting period is independent of the strength of the initial perturbation. The addition of anisotropic thermal conduction only leads to an increase in the mean value for the period, in agreement with our previous study. We also consider a different type of initial driver and we obtain an oscillation period matching the independent trend previously mentioned. Thus, we report for the first time on the independence between the type and strength of the initializing wave pulse and the resulting period of oscillatory reconnection in a hot coronal plasma. This makes oscillatory reconnection a promising mechanism to be used within the context of coronal seismology. Title: Oscillatory Reconnection of a 2D X-point in a hot coronal plasma Authors: Karampelas, Konstantinos; Botha, Gert J. J.; Regnier, Stephane; Mclaughlin, James A. Bibcode: 2022cosp...44.2559K Altcode: Oscillatory reconnection (a relaxation mechanism with periodic changes in connectivity) has been proposed as a potential physical mechanism underpinning several periodic phenomena in the solar atmosphere including, but not limited to, quasi-periodic pulsations (QPPs) and flows. In the past, this mechanism had been extensively studied numerically for 2D and 3D simulations of null points in cold plasma. In our latest studies, we have expanded our understanding of oscillatory reconnection, by considering for the first time hot, coronal plasma. We will be presenting our latest results, from numerically solving the fully-compressive, resistive MHD equations for a 2D magnetic X-point under coronal conditions using the PLUTO code. We report on the resulting oscillatory reconnection including its periodicity and decay rate, by tracking the evolution of the current density profile at the null point. We also consider, for the first time, the effect of adding anisotropic thermal conduction to the mechanism, and how it simplifies the spectrum of the oscillation profile and increases its decay rate, while still allowing the mechanism to manifest. Finally, we reveal how the equilibrium magnetic field strength, density distribution and the amplitude of the initial perturbation relate to the decay rate, and period of oscillatory reconnection, opening the tantalising possibility of utilizing oscillatory reconnection as a seismological tool. Title: Using Oscillatory Reconnection of a 2D X-point as a tool for coronal seismology. Authors: Karampelas, Konstantinos; Botha, Gert J. J.; Regnier, Stephane; Mclaughlin, James A. Bibcode: 2022cosp...44.2487K Altcode: The mechanism of oscillatory reconnection of a null point has been one of the proposed mechanisms behind phenomena like quasi-periodic pulsations (QPPs). The manifestation of this mechanism through the interaction of the ubiquitous waves with null points in the solar atmosphere opens the possibility of utilizing oscillatory reconnection as a tool for coronal seismology. In the past, the first steps had been taken, by connecting the length of the initial current sheet with the period of oscillatory reconnection, and by identifying a linear regime where the period is affected by resistivity. Our recent numerical studies have expanded upon these findings, by considering plasma at coronal conditions, with the addition of anisotropic thermal conduction. We have performed a series of parameter studies with the use of the PLUTO code, which reveal a relation between the equilibrium magnetic field strength and density distribution with the period and decay rate of oscillatory reconnection. In addition, we see an independence of the oscillation period from the type and strength of the external wave pulse, which perturbs the null from its initial equilibrium state. This allows us to formulate an empirical formula connecting these four quantities, opening the way in using oscillatory reconnection for coronal seismology. Title: Oscillatory Reconnection of a 2D X-point in a Hot Coronal Plasma Authors: Karampelas, Konstantinos; McLaughlin, James A.; Botha, Gert J. J.; Régnier, Stéphane Bibcode: 2022ApJ...925..195K Altcode: 2021arXiv211205712K Oscillatory reconnection (a relaxation mechanism with periodic changes in connectivity) has been proposed as a potential physical mechanism underpinning several periodic phenomena in the solar atmosphere, including, but not limited to, quasi-periodic pulsations (QPPs). Despite its importance, however, the mechanism has never been studied within a hot, coronal plasma. We investigate oscillatory reconnection in a one million Kelvin plasma by solving the fully-compressive, resistive MHD equations for a 2D magnetic X-point under coronal conditions using the PLUTO code. We report on the resulting oscillatory reconnection including its periodicity and decay rate. We observe a more complicated oscillating profile for the current density compared to that found for a cold plasma, due to mode-conversion at the equipartition layer. We also consider, for the first time, the effect of adding anisotropic thermal conduction to the oscillatory reconnection mechanism, and we find this simplifies the spectrum of the oscillation profile and increases the decay rate. Crucially, the addition of thermal conduction does not prevent the oscillatory reconnection mechanism from manifesting. Finally, we reveal a relationship between the equilibrium magnetic field strength, decay rate, and period of oscillatory reconnection, which opens the tantalising possibility of utilizing oscillatory reconnection as a seismological tool. Title: Multi-Stranded Coronal Loops: Quantifying Strand Number and Heating Frequency from Simulated Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) Observations Authors: Williams, Thomas; Walsh, Robert W.; Regnier, Stephane; Johnston, Craig D. Bibcode: 2021SoPh..296..102W Altcode: 2021arXiv210512499W Coronal loops form the basic building blocks of the magnetically closed solar corona yet much is still to be determined concerning their possible fine-scale structuring and the rate of heat deposition within them. Using an improved multi-stranded loop model to better approximate the numerically challenging transition region, this article examines synthetic NASA Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) emission simulated in response to a series of prescribed spatially and temporally random, impulsive and localised heating events across numerous sub-loop elements with a strong weighting towards the base of the structure: the nanoflare heating scenario. The total number of strands and nanoflare repetition times is varied systematically in such a way that the total energy content remains approximately constant across all the cases analysed. Repeated time-lag detection during an emission time series provides a good approximation for the nanoflare repetition time for low-frequency heating. Furthermore, using a combination of AIA 171/193 and 193/211 channel ratios in combination with spectroscopic determination of the standard deviation of the loop-apex temperature over several hours alongside simulations from the outlined multi-stranded loop model, it is demonstrated that both the imposed heating rate and number of strands can be realised. Title: Damping of Propagating Kink Waves in the Solar Corona Authors: Tiwari, Ajay K.; Morton, Richard J.; Régnier, Stéphane; McLaughlin, James A. Bibcode: 2019ApJ...876..106T Altcode: 2019arXiv190408834T Alfvénic waves have gained renewed interest since the existence of ubiquitous propagating kink waves were discovered in the corona. It has long been suggested that Alfvénic waves play an important role in coronal heating and the acceleration of the solar wind. To this effect, it is imperative to understand the mechanisms that enable their energy to be transferred to the plasma. Mode conversion via resonant absorption is believed to be one of the main mechanisms for kink wave damping and it is considered to play a key role in the process of energy transfer. This study examines the damping of propagating kink waves in quiescent coronal loops using the Coronal Multi-channel Polarimeter. A coherence-based method is used to track the Doppler velocity signal of the waves, which enables us to investigate the spatial evolution of velocity perturbations. The power ratio of outward to inward propagating waves is used to estimate the associated damping lengths and quality factors. To enable accurate estimates of these quantities, we provide the first derivation of a likelihood function suitable for fitting models to the ratio of two power spectra obtained from discrete Fourier transforms. Maximum likelihood estimation is used to fit an exponential damping model to the observed variation in power ratio as a function of frequency. We confirm earlier indications that propagating kink waves are undergoing frequency-dependent damping. Additionally, we find that the rate of damping decreases, or equivalently the damping length increases, for longer coronal loops that reach higher in the corona. Title: In situ generation of coronal Alfvén waves by jets Authors: González-Avilés, J. J.; Guzmán, F. S.; Fedun, V.; Verth, G.; Sharma, R.; Shelyag, S.; Regnier, S. Bibcode: 2019MNRAS.484.1936G Altcode: 2019MNRAS.tmp...67G; 2018arXiv180704224G Within the framework of 3D resistive magnetohydrodynamic, we simulate the formation of a plasma jet with the morphology, upward velocity up to 130 km s-1, and time-scale formation between 60 and 90 s after beginning of simulation, similar to those expected for type II spicules. Initial results of this simulation were published in paper by, e.g. González-Avilés et al. (2018), and present paper is devoted to the analysis of transverse displacements and rotational-type motion of the jet. Our results suggest that 3D magnetic reconnection may be responsible for the formation of the jet in paper by González-Avilés et al. (2018). In this paper, by calculating times series of the velocity components vx and vy in different points near to the jet for various heights we find transverse oscillations in agreement with spicule observations. We also obtain a time-distance plot of the temperature in a cross-cut at the plane x = 0.1 Mm and find significant transverse displacements of the jet. By analysing temperature isosurfaces of 104 K with the distribution of vx, we find that if the line-of-sight (LOS) is approximately perpendicular to the jet axis then there is both motion towards and away from the observer across the width of the jet. This red-blue shift pattern of the jet is caused by rotational motion, initially clockwise and anti-clockwise afterwards, which could be interpreted as torsional motion and may generate torsional Alfvén waves in the corona region. From a nearly vertical perspective of the jet the LOS velocity component shows a central blue-shift region surrounded by red-shifted plasma. Title: Erratum: Correction to: Statistical Analysis of Solar Events Associated with Storm Sudden Commencements over One Year of Solar Maximum During Cycle 23: Propagation from the Sun to the Earth and Effects Authors: Bocchialini, K.; Grison, B.; Menvielle, M.; Chambodut, A.; Cornilleau-Wehrlin, N.; Fontaine, D.; Marchaudon, A.; Pick, M.; Pitout, F.; Schmieder, B.; Régnier, S.; Zouganelis, I. Bibcode: 2019SoPh..294...38B Altcode: Correction to: Solar Phys (2018) 293:75https://doi.org/10.1007/s11207-018-1278-5

Please find in this correction document the correct versions of abstract, Sect. 3.1 and Figs. 3 and 12. Title: Statistical Analysis of Solar Events Associated with Storm Sudden Commencements over One Year of Solar Maximum During Cycle 23: Propagation from the Sun to the Earth and Effects Authors: Bocchialini, K.; Grison, B.; Menvielle, M.; Chambodut, A.; Cornilleau-Wehrlin, N.; Fontaine, D.; Marchaudon, A.; Pick, M.; Pitout, F.; Schmieder, B.; Régnier, S.; Zouganelis, I. Bibcode: 2018SoPh..293...75B Altcode: 2018arXiv180307593B Taking the 32 storm sudden commencements (SSCs) listed by the International Service of Geomagnetic Indices (ISGI) of the Observatory de l'Ebre during 2002 (solar activity maximum in Cycle 23) as a starting point, we performed a multi-criterion analysis based on observations (propagation time, velocity comparisons, sense of the magnetic field rotation, radio waves) to associate them with solar sources, identified their effects in the interplanetary medium, and looked at the response of the terrestrial ionized and neutral environment. We find that 28 SSCs can be related to 44 coronal mass ejections (CMEs), 15 with a unique CME and 13 with a series of multiple CMEs, among which 19 (68%) involved halo CMEs. Twelve of the 19 fastest CMEs with speeds greater than 1000 km s−1 are halo CMEs. For the 44 CMEs, including 21 halo CMEs, the corresponding X-ray flare classes are: 3 X-class, 19 M-class, and 22 C-class flares. The probability for an SSC to occur is 75% if the CME is a halo CME. Among the 500, or even more, front-side, non-halo CMEs recorded in 2002, only 23 could be the source of an SSC, i.e. 5%. The complex interactions between two (or more) CMEs and the modification of their trajectories have been examined using joint white-light and multiple-wavelength radio observations. The detection of long-lasting type IV bursts observed at metric-hectometric wavelengths is a very useful criterion for the CME-SSC events association. The events associated with the most depressed Dst values are also associated with type IV radio bursts. The four SSCs associated with a single shock at L1 correspond to four radio events exhibiting characteristics different from type IV radio bursts. The solar-wind structures at L1 after the 32 SSCs are 12 magnetic clouds (MCs), 6 interplanetary coronal mass ejections (ICMEs) without an MC structure, 4 miscellaneous structures, which cannot unambiguously be classified as ICMEs, 5 corotating or stream interaction regions (CIRs/SIRs), one CIR caused two SSCs, and 4 shock events; note than one CIR caused two SSCs. The 11 MCs listed in 3 or more MC catalogs covering the year 2002 are associated with SSCs. For the three most intense geomagnetic storms (based on Dst minima) related to MCs, we note two sudden increases of the Dst, at the arrival of the sheath and the arrival of the MC itself. In terms of geoeffectiveness, the relation between the CME speed and the magnetic-storm intensity, as characterized using the Dst magnetic index, is very complex, but generally CMEs with velocities at the Sun larger than 1000 km s−1 have larger probabilities to trigger moderate or intense storms. The most geoeffective events are MCs, since 92% of them trigger moderate or intense storms, followed by ICMEs (33%). At best, CIRs/SIRs only cause weak storms. We show that these geoeffective events (ICMEs or MCs) trigger an increased and combined auroral kilometric radiation (AKR) and non-thermal continuum (NTC) wave activity in the magnetosphere, an enhanced convection in the ionosphere, and a stronger response in the thermosphere. However, this trend does not appear clearly in the coupling functions, which exhibit relatively weak correlations between the solar-wind energy input and the amplitude of various geomagnetic indices, whereas the role of the southward component of the solar-wind magnetic field is confirmed. Some saturation appears for Dst values <−100 nT on the integrated values of the polar and auroral indices. Title: I. Jet Formation and Evolution Due to 3D Magnetic Reconnection Authors: González-Avilés, J. J.; Guzmán, F. S.; Fedun, V.; Verth, G.; Shelyag, S.; Regnier, S. Bibcode: 2018ApJ...856..176G Altcode: 2017arXiv170905066G Using simulated data-driven, 3D resistive MHD simulations of the solar atmosphere, we show that 3D magnetic reconnection may be responsible for the formation of jets with the characteristics of Type II spicules. We numerically model the photosphere-corona region using the C7 equilibrium atmosphere model. The initial magnetic configuration is a 3D potential magnetic field, extrapolated up to the solar corona region from a dynamic realistic simulation of the solar photospheric magnetoconvection model that mimics the quiet-Sun. In this case, we consider a uniform and constant value of the magnetic resistivity of 12.56 Ω m. We have found that the formation of the jet depends on the Lorentz force, which helps to accelerate the plasma upward. Analyzing various properties of the jet dynamics, we found that the jet structure shows a Doppler shift close to regions with high vorticity. The morphology, the upward velocity covering a range up to 130 km s-1, and the timescale formation of the structure between 60 and 90 s, are similar to those expected for Type II spicules. Title: Statistical analysis of solar events associated with SSC over year of solar maximum during cycle 23: 2. Characterisation on the Sun-Earth path - Geoeffectiveness Authors: Cornilleau-Wehrlin, N.; Bocchialini, K.; Menvielle, M.; Fontaine, D.; Grison, B.; Marchaudon, A.; Pick, M.; Pitout, F.; Schmieder, B.; Regnier, S.; Zouganelis, Y.; Chambodut, A. Bibcode: 2017AGUFMSH31A2712C Altcode: Taking the 32 sudden storm commencements (SSC) listed by the observatory de l'Ebre / ISGI over the year 2002 (maximal solar activity) as a starting point, we performed a statistical analysis of the related solar sources, solar wind signatures, and terrestrial responses. For each event, we characterized and identified, as far as possible, (i) the sources on the Sun (Coronal Mass Ejections -CME-), with the help of a series of criteria (velocities, drag coefficient, radio waves, magnetic field polarity), as well as (ii) the structure and properties in the interplanetary medium, at L1, of the event associated to the SSC: magnetic clouds -MC-, non-MC interplanetary coronal mass ejections -ICME-, co-rotating/stream interaction regions -SIR/CIR-, shocks only and unclear events that we call "miscellaneous" events. The geoeffectiveness of the events, classified by category at L1, is analysed by their signatures in the Earth ionized (magnetosphere and ionosphere) and neutral (thermosphere) environments, using a broad set of in situ, remote and ground based instrumentation. The role of the presence of a unique or of a multiple source at the Sun, of its nature, halo or non halo CME, is also discussed. The set of observations is statistically analyzed so as to evaluate and compare the geoeffectiveness of the events. The results obtained for this set of geomagnetic storms started by SSCs is compared to the overall statistics of year 2002, relying on already published catalogues of events, allowing assessing the relevance of our approach ; for instance all the 12 well identified Magnetic Clouds of 2002 give rise to SSCs. Title: Statistical Analysis of Solar Events Associated with Storm Sudden Commencements over One Year of Solar Maximum during Cycle 23: Propagation and Effects from the Sun to the Earth. Authors: Bocchialini, K.; Grison, B.; Menvielle, M.; Chambodut, A.; Cornilleau-Wehrlin, N.; Fontaine, D.; Marchaudon, A.; Pick, M.; Pitout, F.; Schmieder, B.; Régnier, S.; Zouganelis, I. Bibcode: 2017sf2a.conf..181B Altcode: From the list of 32 SSCs over the year 2002, we performed a multi-criteria analysis based on propagation time, velocity comparison, sense of the magnetic field rotation, radio waves to associate them with solar sources, identify their causes in the interplanetary medium and then look at the response of the terrestrial ionized and neutral environment to them. The complex interactions between two (or more) CMEs and the modification in their trajectory have been examined using joint white light and multiple-wavelength radio observations. The structures at L_1 after the 32 SSCs are regarded as Magnetic Clouds (MCs), ICMEs without a MC structure, Miscellaneous structures, CIRs/SIRs, and shock-only events. In terms of geoeffectivity, generally CMEs with velocities at the Sun larger than 1000 km.s-1 have larger probabilities to trigger moderate or intense storms. The most geoeffective events are MCs, since 92% of them trigger moderate or intense storms. The geoeffective events trigger an increased and combined AKR and NTC wave activity in the magnetosphere, an enhanced convection in the ionosphere and a stronger response in the thermosphere. Title: Statistical Analysis of Solar Events Associated with SSC over Year of Solar Maximum during Cycle 23: 1. Identification of Related Sun-Earth Events Authors: Grison, B.; Bocchialini, K.; Menvielle, M.; Chambodut, A.; Cornilleau-Wehrlin, N.; Fontaine, D.; Marchaudon, A.; Pick, M.; Pitout, F.; Schmieder, B.; Regnier, S.; Zouganelis, Y. Bibcode: 2017AGUFMSH31A2711G Altcode: Taking the 32 sudden storm commencements (SSC) listed by the observatory de l'Ebre / ISGI over the year 2002 (maximal solar activity) as a starting point, we performed a statistical analysis of the related solar sources, solar wind signatures, and terrestrial responses. For each event, we characterized and identified, as far as possible, (i) the sources on the Sun (Coronal Mass Ejections -CME-), with the help of a series of herafter detailed criteria (velocities, drag coefficient, radio waves, polarity), as well as (ii) the structure and properties in the interplanetary medium, at L1, of the event associated to the SSC: magnetic clouds -MC-, non-MC interplanetary coronal mass ejections -ICME-, co-rotating/stream interaction regions -SIR/CIR-, shocks only and unclear events that we call "miscellaneous" events. The categorization of the events at L1 is made on published catalogues. For each potential CME/L1 event association we compare the velocity observed at L1 with the one observed at the Sun and the estimated balistic velocity. Observations of radio emissions (Type II, Type IV detected from the ground and /or by WIND) associated to the CMEs make the solar source more probable. We also compare the polarity of the magnetic clouds with the hemisphere of the solar source. The drag coefficient (estimated with the drag-based model) is calculated for each potential association and it is compared to the expected range values. We identified a solar source for 26 SSC related events. 12 of these 26 associations match all criteria. We finally discuss the difficulty to perform such associations. Title: I. Jet Formation and Evolution due to 3D Magnetic Reconnection Authors: González, J. J.; Guzmán, F.; Fedun, V.; Verth, G.; Shelyag, S.; Regnier, S. Bibcode: 2017AGUFMSH43A2807G Altcode: Using simulated data-driven three-dimensional resistive MHD simulations of the solar atmosphere, we show that magnetic reconnection can be responsible of the formation of jets with characteristic of Type II spicules. For this, we numerically model the photosphere-corona region using the C7 equilibrium atmosphere model. The initial magnetic configuration is a 3D potential magnetic field, extrapolated up to the solar corona region from a dynamic realistic simulation of solar photospheric magnetoconvection model which is mimicking quiet-Sun. In this case we consider a uniform and constant value of the magnetic resistivity of 12.56 Ω m. We have found that formation of the jets depends on the Lorentz force, which helps to accelerate the plasma upwards. Analyzing various properties of the jet dynamics, we found that the jet structure shows Doppler shift near to regions with high vorticity. The morphology, upward velocity, covering a range up to 100 km s-1, and life-time of the estructure, bigger than 100 s, are similar to those expected for Type II spicules. Title: Observational Signatures of a Kink-unstable Coronal Flux Rope Using Hinode/EIS Authors: Snow, B.; Botha, G. J. J.; Régnier, S.; Morton, R. J.; Verwichte, E.; Young, P. R. Bibcode: 2017ApJ...842...16S Altcode: 2017arXiv170505114S The signatures of energy release and energy transport for a kink-unstable coronal flux rope are investigated via forward modeling. Synthetic intensity and Doppler maps are generated from a 3D numerical simulation. The CHIANTI database is used to compute intensities for three Hinode/EIS emission lines that cover the thermal range of the loop. The intensities and Doppler velocities at simulation-resolution are spatially degraded to the Hinode/EIS pixel size (1″), convolved using a Gaussian point-spread function (3″), and exposed for a characteristic time of 50 s. The synthetic images generated for rasters (moving slit) and sit-and-stare (stationary slit) are analyzed to find the signatures of the twisted flux and the associated instability. We find that there are several qualities of a kink-unstable coronal flux rope that can be detected observationally using Hinode/EIS, namely the growth of the loop radius, the increase in intensity toward the radial edge of the loop, and the Doppler velocity following an internal twisted magnetic field line. However, EIS cannot resolve the small, transient features present in the simulation, such as sites of small-scale reconnection (e.g., nanoflares). Title: Statistical analysis of solar events associated with SSC over one year of solar maximum during cycle 23: propagation and effects from the Sun to the Earth Authors: Cornilleau-Wehrlin, Nicole; Bocchialini, Karine; Menvielle, Michel; Chambodut, Aude; Fontaine, Dominique; Grison, Benjamin; Marchaudon, Aurélie; Pick, Monique; Pitout, Frédéric; Schmieder, Brigitte; Régnier, Stéphane; Zouganelis, Yannis Bibcode: 2017EGUGA..19.3689C Altcode: Taking the 32 sudden storm commencements (SSC) listed by the observatory de l'Ebre / ISGI over the year 2002 (maximal solar activity) as a starting point, we performed a statistical analysis of the related solar sources, solar wind signatures, and terrestrial responses. For each event, we characterized and identified, as far as possible, (i) the sources on the Sun (Coronal Mass Ejections -CME-), with the help of a series of criteria (velocities, drag coefficient, radio waves, helicity), as well as (ii) the structure and properties in the interplanetary medium, at L1, of the event associated to the SSC: magnetic clouds -MC-, non-MC interplanetary coronal mass ejections -ICME-, co-rotating/stream interaction regions -SIR/CIR-, shocks only and unclear events that we call "miscellaneous" events. The observed Sun-to-Earth travel times are compared to those estimated using existing simple models of propagation in the interplanetary medium. This comparison is used to statistically assess performances of various models. The geoeffectiveness of the events, classified by category at L1, is analysed by their signatures in the Earth ionized (magnetosphere and ionosphere) and neutral (thermosphere) environments, using a broad set of in situ, remote and ground based instrumentation. The role of the presence of a unique or of a multiple source at the Sun, of its nature, halo or non halo CME, is also discussed. The set of observations is statistically analyzed so as to evaluate and compare the geoeffectiveness of the events. The results obtained for this set of geomagnetic storms started by SSCs is compared to the overall statistics of year 2002, relying on already published catalogues of events, allowing assessing the relevance of our approach (for instance the all 12 well identified Magnetic Clouds of 2002 give rise to SSCs). Title: Magnetic evolution of emerging active region 11856 using a potential field model Authors: Rolling, Autumn; Régnier, Stéphane Bibcode: 2017psio.confE.114R Altcode: No abstract at ADS Title: Exploring Coronal Dynamics: A Next Generation Solar Physics Mission white paper Authors: Morton, R. J.; Scullion, E.; Bloomfield, D. S.; McLaughlin, J. A.; Regnier, S.; McIntosh, S. W.; Tomczyk, S.; Young, P. Bibcode: 2016arXiv161106149M Altcode: Determining the mechanisms responsible for the heating of the coronal plasma and maintaining and accelerating the solar wind are long standing goals in solar physics. There is a clear need to constrain the energy, mass and momentum flux through the solar corona and advance our knowledge of the physical process contributing to these fluxes. Furthermore, the accurate forecasting of Space Weather conditions at the near-Earth environment and, more generally, the plasma conditions of the solar wind throughout the heliosphere, require detailed knowledge of these fluxes in the near-Sun corona. Here we present a short case for a space-based imaging-spectrometer coronagraph, which will have the ability to provide synoptic information on the coronal environment and provide strict constraints on the mass, energy, and momentum flux through the corona. The instrument would ideally achieve cadences of $\sim10$~s, spatial resolution of 1" and observe the corona out to 2~$R_{\sun}$. Such an instrument will enable significant progress in our understanding of MHD waves throughout complex plasmas, as well as potentially providing routine data products to aid Space Weather forecasting. Title: 3D WKB solution for fast magnetoacoustic wave behaviour around an X-line Authors: McLaughlin, J. A.; Botha, G. J. J.; Régnier, S.; Spoors, D. L. Bibcode: 2016A&A...591A.103M Altcode: 2016arXiv160702379M Context. We study the propagation of a fast magnetoacoustic wave in a 3D magnetic field created from two magnetic dipoles. The magnetic topology contains an X-line.
Aims: We aim to contribute to the overall understanding of MHD wave propagation within inhomogeneous media, specifically around X-lines.
Methods: We investigate the linearised, 3D MHD equations under the assumptions of ideal and cold plasma. We utilise the WKB approximation and Charpit's method during our investigation.
Results: It is found that the behaviour of the fast magnetoacoustic wave is entirely dictated by the local, inhomogeneous, equilibrium Alfvén speed profile. All parts of the wave experience refraction during propagation, where the magnitude of the refraction effect depends on the location of an individual wave element within the inhomogeneous magnetic field. The X-line, along which the Alfvén speed is identically zero, acts as a focus for the refraction effect. There are two main types of wave behaviour: part of the wave is either trapped by the X-line or escapes the system, and there exists a critical starting region around the X-line that divides these two types of behaviour. For the set-up investigated, it is found that 15.5% of the fast wave energy is trapped by the X-line.
Conclusions: We conclude that linear, β = 0 fast magnetoacoustic waves can accumulate along X-lines and thus these will be specific locations of fast wave energy deposition and thus preferential heating. The work here highlights the importance of understanding the magnetic topology of a system. We also demonstrate how the 3D WKB technique described in this paper can be applied to other magnetic configurations. Title: The Influence of Spatial resolution on Nonlinear Force-free Modeling Authors: DeRosa, M. L.; Wheatland, M. S.; Leka, K. D.; Barnes, G.; Amari, T.; Canou, A.; Gilchrist, S. A.; Thalmann, J. K.; Valori, G.; Wiegelmann, T.; Schrijver, C. J.; Malanushenko, A.; Sun, X.; Régnier, S. Bibcode: 2015ApJ...811..107D Altcode: 2015arXiv150805455D The nonlinear force-free field (NLFFF) model is often used to describe the solar coronal magnetic field, however a series of earlier studies revealed difficulties in the numerical solution of the model in application to photospheric boundary data. We investigate the sensitivity of the modeling to the spatial resolution of the boundary data, by applying multiple codes that numerically solve the NLFFF model to a sequence of vector magnetogram data at different resolutions, prepared from a single Hinode/Solar Optical Telescope Spectro-Polarimeter scan of NOAA Active Region 10978 on 2007 December 13. We analyze the resulting energies and relative magnetic helicities, employ a Helmholtz decomposition to characterize divergence errors, and quantify changes made by the codes to the vector magnetogram boundary data in order to be compatible with the force-free model. This study shows that NLFFF modeling results depend quantitatively on the spatial resolution of the input boundary data, and that using more highly resolved boundary data yields more self-consistent results. The free energies of the resulting solutions generally trend higher with increasing resolution, while relative magnetic helicity values vary significantly between resolutions for all methods. All methods require changing the horizontal components, and for some methods also the vertical components, of the vector magnetogram boundary field in excess of nominal uncertainties in the data. The solutions produced by the various methods are significantly different at each resolution level. We continue to recommend verifying agreement between the modeled field lines and corresponding coronal loop images before any NLFFF model is used in a scientific setting. Title: A new approach to the maser emission in the solar corona Authors: Régnier, S. Bibcode: 2015A&A...581A...9R Altcode: 2015arXiv150707350R
Aims: The electron plasma frequency ωpe and electron gyrofrequency Ωe are two parameters that allow us to describe the properties of a plasma and to constrain the physical phenomena at play, for instance, whether a maser instability develops. In this paper, we aim to show that the maser instability can exist in the solar corona.
Methods: We perform an in-depth analysis of the ωpee ratio for simple theoretical and complex solar magnetic field configurations. Using the combination of force-free models for the magnetic field and hydrostatic models for the plasma properties, we determine the ratio of the plasma frequency to the gyrofrequency for electrons. For the sake of comparison, we compute the ratio for bipolar magnetic fields containing a twisted flux bundle, and for four different observed active regions. We also study how ωpee is affected by the potential and non-linear force-free field models.
Results: We demonstrate that the ratio of the plasma frequency to the gyrofrequency for electrons can be estimated by this novel method combining magnetic field extrapolation techniques and hydrodynamic models. Even if statistically not significant, values of ωpee≤ 1 are present in all examples, and are located in the low corona near to photosphere below one pressure scale-height and/or in the vicinity of twisted flux bundles. The values of ωpee are lower for non-linear force-free fields than potential fields, thus increasing the possibility of maser instability in the corona.
Conclusions: From this new approach for estimating ωpee, we conclude that the electron maser instability can exist in the solar corona above active regions. The importance of the maser instability in coronal active regions depends on the complexity and topology of the magnetic field configurations. Title: Chromospheric seismology above sunspot umbrae Authors: Snow, B.; Botha, G. J. J.; Régnier, S. Bibcode: 2015A&A...580A.107S Altcode: 2015arXiv150707371S Context. The acoustic resonator is an important model for explaining the three-minute oscillations in the chromosphere above sunspot umbrae. The steep temperature gradients at the photosphere and transition region provide the cavity for the acoustic resonator, which allows waves to be both partially transmitted and partially reflected.
Aims: In this paper, a new method of estimating the size and temperature profile of the chromospheric cavity above a sunspot umbra is developed.
Methods: The magnetic field above umbrae is modelled numerically in 1.5D with slow magnetoacoustic wave trains travelling along magnetic fieldlines. Resonances are driven by applying the random noise of three different colours - white, pink, and brown - as small velocity perturbations to the upper convection zone. Energy escapes the resonating cavity and generates wave trains moving into the corona. Line-of-sight integration is also performed to determine the observable spectra through SDO/AIA.
Results: The numerical results show that the gradient of the coronal spectra is directly correlated with the chromosperic temperature configuration. As the chromospheric cavity size increases, the spectral gradient becomes shallower. When line-of-sight integration is performed, the resulting spectra demonstrate a broadband of excited frequencies that is correlated with the chromospheric cavity size. The broadband of excited frequencies becomes narrower as the chromospheric cavity size increases.
Conclusions: These two results provide a potentially useful diagnostic for the chromospheric temperature profile by considering coronal velocity oscillations. Title: Thermal properties of cooling multi-stranded coronal loops Authors: Regnier, S.; Alexander, C. E.; Walsh, R. W. Bibcode: 2014AGUFMSH13C4132R Altcode: Solar coronal loops are subject to different thermal processes such as heating, cooling, plasma condensation or plasma evaporation. Based on a multi-stranded model of coronal loops satisfying the one-dimensional hydrodynamics equations, we study the cooling of coronal loops from a steady state. We perform the analysis of the cooling phases by comparing the evolution of the loops in different SDO/AIA EUV channels. The appearance and timing of the cooling in a SDO/AIA channel depend on the initial thermodynamics parameters of the loop: hotter is the loop, faster the loop will cool. Therefore, based the temperature response function of individual filters, we deduce the temperature of the steady-state loop from the ordering of the observed light curves. The time evolution of the temperature during the cooling phase can also be approximated from the light curves. This method providing a temperature diagnostic of coronal loops is successfully applied to published data of flaring loops. Title: Red and Blueshifts in Multi-stranded Coronal Loops: A New Temperature Diagnostic Authors: Regnier, S.; Walsh, R. W. Bibcode: 2014arXiv1405.3450R Altcode: Based on observations from the EUV Imaging Spectrometer (EIS) on board Hinode, the existence of a broad distribution of blue and red Dopplershift in active region loops has been revealed; the distribution of Dopplershifts depends on the peak temperature of formation of the observed spectral lines. To reproduce those observations, we use a nanoflare heating model for multi-stranded coronal loops (Sarkar and Walsh 2008, 2009) and a set of spectral lines covering a broad range of temperature (from 0.25 MK to 5.6 MK). We first show that red- and blueshifts are ubiquitous in all wavelength ranges; redshifts/downflows dominating cool spectral lines (from O V to Si VII) and blueshifts/upflows dominating the hot lines (from Fe XV to Ca XVII). These Dopplershifts are indicative of plasma condensation and evaporation. By computing the average Dopplershift, we derive a new temperature diagnostic for coronal loops: the temperature at which the average Dopplershift vanishes estimates the mean temperature of the plasma along the coronal loop and at the footpoints. To compare closely with observations, we model dense and sparse Hinode/EIS rasters at the instrument resolution. The temperature diagnostic provides the same temperature estimates as the model whatever the type of raster or the viewing angle. To conclude, we have developed a robust temperature diagnostic to measure the plasma temperature of a coronal loop using a broad range of spectral lines. Title: Sparkling Extreme-ultraviolet Bright Dots Observed with Hi-C Authors: Régnier, S.; Alexander, C. E.; Walsh, R. W.; Winebarger, A. R.; Cirtain, J.; Golub, L.; Korreck, K. E.; Mitchell, N.; Platt, S.; Weber, M.; De Pontieu, B.; Title, A.; Kobayashi, K.; Kuzin, S.; DeForest, C. E. Bibcode: 2014ApJ...784..134R Altcode: 2014arXiv1402.2457R Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 Å. One of them is the existence of short, small brightenings "sparkling" at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale, trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 1026 erg. Title: Magnetic Field Extrapolations into the Corona: Success and Future Improvements Authors: Régnier, S. Bibcode: 2013SoPh..288..481R Altcode: 2013arXiv1307.3844R The solar atmosphere being magnetic in nature, the understanding of the structure and evolution of the magnetic field in different regions of the solar atmosphere has been an important task over the past decades. This task has been made complicated by the difficulties to measure the magnetic field in the corona, while it is currently known with a good accuracy in the photosphere and/or chromosphere. Thus, to determine the coronal magnetic field, a mathematical method has been developed based on the observed magnetic field. This is the so-called magnetic field extrapolation technique. This technique relies on two crucial points: i) the physical assumption leading to the system of differential equations to be solved, ii) the choice and quality of the associated boundary conditions. In this review, I summarise the physical assumptions currently in use and the findings at different scales in the solar atmosphere. I concentrate the discussion on the extrapolation techniques applied to solar magnetic data and the comparison with observations in a broad range of wavelengths (from hard X-rays to radio emission). Title: Measuring the Magnetic-Field Strength of the Quiet Solar Corona Using "EIT Waves" Authors: Long, D. M.; Williams, D. R.; Régnier, S.; Harra, L. K. Bibcode: 2013SoPh..288..567L Altcode: 2013arXiv1305.5169L Variations in the propagation of globally propagating disturbances (commonly called "EIT waves") through the low solar corona offer a unique opportunity to probe the plasma parameters of the solar atmosphere. Here, high-cadence observations of two "EIT wave" events taken using the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) are combined with spectroscopic measurements from the Extreme ultraviolet Imaging Spectrometer (EIS) onboard the Hinode spacecraft and used to examine the variability of the quiet coronal magnetic-field strength. The combination of pulse kinematics from SDO/AIA and plasma density from Hinode/EIS is used to show that the magnetic-field strength is in the range ≈ 2 - 6 G in the quiet corona. The magnetic-field estimates are then used to determine the height of the pulse, allowing a direct comparison with theoretical values obtained from magnetic-field measurements from the Helioseismic and Magnetic Imager (HMI) onboard SDO using global-scale PFSS and local-scale extrapolations. While local-scale extrapolations predict heights inconsistent with prior measurements, the agreement between observations and the PFSS model indicates that "EIT waves" are a global phenomenon influenced by global-scale magnetic field. Title: Anti-parallel EUV Flows Observed along Active Region Filament Threads with Hi-C Authors: Alexander, Caroline E.; Walsh, Robert W.; Régnier, Stéphane; Cirtain, Jonathan; Winebarger, Amy R.; Golub, Leon; Kobayashi, Ken; Platt, Simon; Mitchell, Nick; Korreck, Kelly; DePontieu, Bart; DeForest, Craig; Weber, Mark; Title, Alan; Kuzin, Sergey Bibcode: 2013ApJ...775L..32A Altcode: 2013arXiv1306.5194A Plasma flows within prominences/filaments have been observed for many years and hold valuable clues concerning the mass and energy balance within these structures. Previous observations of these flows primarily come from Hα and cool extreme-ultraviolet (EUV) lines (e.g., 304 Å) where estimates of the size of the prominence threads has been limited by the resolution of the available instrumentation. Evidence of "counter-steaming" flows has previously been inferred from these cool plasma observations, but now, for the first time, these flows have been directly imaged along fundamental filament threads within the million degree corona (at 193 Å). In this work, we present observations of an AR filament observed with the High-resolution Coronal Imager (Hi-C) that exhibits anti-parallel flows along adjacent filament threads. Complementary data from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager are presented. The ultra-high spatial and temporal resolution of Hi-C allow the anti-parallel flow velocities to be measured (70-80 km s-1) and gives an indication of the resolvable thickness of the individual strands (0.''8 ± 0.''1). The temperature of the plasma flows was estimated to be log T (K) = 5.45 ± 0.10 using Emission Measure loci analysis. We find that SDO/AIA cannot clearly observe these anti-parallel flows or measure their velocity or thread width due to its larger pixel size. We suggest that anti-parallel/counter-streaming flows are likely commonplace within all filaments and are currently not observed in EUV due to current instrument spatial resolution. Title: Structure and evolution of a unipolar streamer observed by SDO/AIA Authors: Regnier, S. Bibcode: 2013enss.confE.102R Altcode: We report on the observation of unipolar streamer in different wavelength ranges by the SDO/AIA instrument (171A, 193A, 211A, 304A and 335A) observed on July 11, 2012 between 21:30 UT and 23:59 UT. Surrounded by field lines originating in the same polarity, the streamer contains a double-arcade structure, both filled by a prominence with clear evidence of the prominence material sitting in the corona and a cavity. This unipolar streamer is similar to the magnetic field structure described by Torok et al. (ApJ, 2011, 739, L63) for a sympathetic eruption of filaments. The streamer also evidences a pressure build-up on the equatorial side as suggested by the modelling of Riley and Luhmann (Solar Physics, 2012, 277, 355). Title: Dynamic anti-parallel flows observed within an active region filament with SDO/AIA and Hi-C Authors: Alexander, Caroline E.; Regnier, Stephane; Walsh, Robert W.; Hi-C Science Team Bibcode: 2013enss.confE..71A Altcode: Plasma flows within prominences/filaments have been observed for many years and hold valuable clues concerning the mass and energy balance within these structures. Previous observations of these flows primarily come from H-alpha and cool EUV lines (e.g., 304 A) where estimations of the size of the cool prominence threads has been limited by the resolution of the available instrumentation. Evidence of curious `counter-steaming' flows have previously been inferred from observations but now, for the first time, these flows have been directly imaged within the corona. In this work we present observations of an active region filament observed with SDO/AIA and Hi-C that exhibits dynamic anti-parallel flows along side-by-side threads within the structure. The ultra-high spatial resolution of Hi-C allows the individual flow velocities to be measured and complementary data from AIA provides context and allows temperature analysis to take place. Measuring the flow speeds, the spatial scale of the threads, and their emission in different temperature regimes allows us to comment on the physical mechanisms taking place and can help us to understand how these flows relate to the stability of the filament as a whole. Title: Small-scale heating events at the footpoints of coronal loops observed by Hi-C and SDO/AIA Authors: Regnier, S.; Alexander, C. E.; Walsh, R. W.; Hi-C Science Team Bibcode: 2013enss.confE..77R Altcode: Hi-C was sounding rocket dedicated to the observation of the hot EUV corona at high spatial resolution (0.2 arcsec) and high time cadence (5s). The Hi-C instrument flew on July 11, 2012 and provided observations in the 193A channel of a large complex of active regions (NOAA 11519-21). We have discovered small-scale (0.74 Mm) and short duration (25s) brightenings, called EUV bright dots (EBDs) at the edge of the active regions. The comparison with SDO/AIA observations in the 193A channel shows that EBDs can also be observed at the very limit of the noise level. EBDs also exist in the 171A, 211A and 335A channels, and have a small contribution in the 304A channel. This strongly suggests that EBDs are transition region and/or coronal transient features. By comparing with SDO/HMI magnetograms and with the support a potential field extrapolation, the observed EBDs are located in unipolar regions at the foot-points of large-scale trans-equatorial loops. We discuss the viable mechanisms that can produce such a short burst/release of energy by comparing the different time scales of the plasma evolution. Title: Measuring the magnetic field strength of the quiet solar corona using "EIT waves" Authors: Long, David M.; Williams, David R.; Régnier, Stéphane; Harra, Louise K. Bibcode: 2013enss.confE..89L Altcode: Variations in the propagation of globally-propagating disturbances (commonly called "EIT waves") through the low solar corona offer a unique opportunity to probe the plasma parameters of the solar atmosphere. Here, high-cadence observations of two "EIT wave" events taken using SDO/AIA are combined with spectroscopic measurements from Hinode/EIS and used to examine the variability of the quiet coronal magnetic field strength. The combination of pulse kinematics from AIA and plasma density from EIS is used to show that the magnetic field strength is in the range 2-6G in the quiet corona. The magnetic field estimates are then used to determine the height of the pulse, allowing a direct comparison with theoretical values obtained from SDO/HMI magnetic field using PFSS and local-domain extrapolations. While local-scale extrapolations predict heights inconsistent with prior measurements, the agreement between observations and the PFSS model indicates that "EIT waves" are a global phenomenon influenced by global-scale magnetic field. Title: 3D Structure of the Outer Atmosphere: Combining Models and Observations Authors: Régnier, S. Bibcode: 2012ASPC..454..355R Altcode: 2011arXiv1101.3271R In this review, I focus on the structure and evolution of the coronal magnetic fields modelled from observations. The development of instruments measuring the photospheric and chromospheric magnetic fields with a high spatial and time resolutions allows us to improve the modeling of the coronal fields based on extrapolation and evolution techniques. In particular, I detail the advance modelling of quiet-Sun areas, active regions and full-disc evolution. I discuss the structure of coronal magnetic features such as filaments, sigmoids and coronal loops as well as their time evolution and instability. The complexity of the coronal field and the origin of open flux are also investigated in these different areas. Finally I discuss the future improvements in terms of instruments and models required to understand better the coronal field. Title: Thermal shielding of an emerging active region Authors: Régnier, S. Bibcode: 2012A&A...544L..10R Altcode: 2012arXiv1207.3992R Context. The interaction between emerging active regions and the pre-existing coronal magnetic field is important for better understanding the mechanisms of storage and release of magnetic energy from the convection zone to the high corona.
Aims: We describe the first steps of an emerging active region within a pre-existing quiet-Sun corona in terms of the thermal and magnetic structure.
Methods: We used unprecedented spatial, temporal and spectral coverage from the Atmospheric Imager Assembly (AIA) and from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO).
Results: Starting on 30 May 2010 at 17:00 UT, we followed the emerging active region AR11076 within a quiet-Sun region for 8 h. Using several SDO/AIA filters that cover temperatures from 50 000 K to 10 MK, we show that the emerging process is characterised by a thermal shield at the interface between the emerging flux and pre-existing quiet-Sun corona.
Conclusions: The active region 11076 is a peculiar example of an emerging active region because (i) the polarities emerge in a photospheric quiet-Sun region near a supergranular-like distribution, and (ii) the polarities that form the bipolar emerging structure do not rotate with respect to each other, which indicates a slight twist in the emerging flux bundle. There is a thermal shield at the interface between the emerging active region and the pre-existing quiet-Sun region. The thermal shielding structure deduced from all SDO/AIA channels is strongly asymmetric between the two polarities of the active region, suggesting that the heating mechanism for one polarity is probably magnetic reconnection, whilst it is caused by increasing magnetic pressure for the opposite polarity.

Appendix A and two movies are available in electronic form at http://www.aanda.org Title: Flows at the Edge of an Active Region: Observation and Interpretation Authors: Boutry, C.; Buchlin, E.; Vial, J. -C.; Régnier, S. Bibcode: 2012ApJ...752...13B Altcode: 2012arXiv1204.1377B Upflows observed at the edges of active regions have been proposed as the source of the slow solar wind. In the particular case of Active Region (AR) 10942, where such an upflow has been already observed, we want to evaluate the part of this upflow that actually remains confined in the magnetic loops that connect AR 10942 to AR 10943. Both active regions were visible simultaneously on the solar disk and were observed by STEREO/SECCHI EUVI. Using Hinode/EIS spectra, we determine the Doppler shifts and densities in AR 10943 and AR 10942 in order to evaluate the mass flows. We also perform magnetic field extrapolations to assess the connectivity between AR 10942 and AR 10943. AR 10943 displays a persistent downflow in Fe XII. Magnetic extrapolations including both ARs show that this downflow can be connected to the upflow in AR 10942. We estimate that the mass flow received by AR 10943 areas connected to AR 10942 represents about 18% of the mass flow from AR 10942. We conclude that the upflows observed on the edge of active regions represent either large-scale loops with mass flowing along them (accounting for about one-fifth of the total mass flow in this example) or open magnetic field structures where the slow solar wind originates. Title: Flows in the Vicinity of Two Active Regions as Seen by Hinode, STEREO, and SoHO Authors: Boutry, C.; Buchlin, E'.; Vial, J.; Régnier, S. Bibcode: 2012ASPC..455...83B Altcode: We observed active region 10943 located at Sun center on February 20, 2007 and we characterized its interactions with active region 10942 by using a multi-instrument comparison between Hinode/XRT and STEREO/SECCHI images, magnetic field maps from SoHO/MDI, and Hinode/EIS spectra from which we built maps of the Doppler shift and the intensity of the Fe XII 195.12 Å line. The results are consistent with some material exchange between the two regions separated by 400″. Title: Magnetic Energy Storage and Current Density Distributions for Different Force-Free Models Authors: Régnier, S. Bibcode: 2012SoPh..277..131R Altcode: 2011arXiv1107.3437R In the last decades, force-free-field modelling has been used extensively to describe the coronal magnetic field and to better understand the physics of solar eruptions at different scales. Especially the evolution of active regions has been studied by successive equilibria in which each computed magnetic configuration is subject to an evolving photospheric distribution of magnetic field and/or electric-current density. This technique of successive equilibria has been successful in describing the rate of change of the energetics for observed active regions. Nevertheless the change in magnetic configuration due to the increase/decrease of electric current for different force-free models (potential, linear and nonlinear force-free fields) has never been studied in detail before. Here we focus especially on the evolution of the free magnetic energy, the location of the excess of energy, and the distribution of electric currents in the corona. For this purpose, we use an idealised active region characterised by four main polarities and a satellite polarity, allowing us to specify a complex topology and sheared arcades to the coronal magnetic field but no twisted flux bundles. We investigate the changes in the geometry and connectivity of field lines, the magnetic energy and current-density content as well as the evolution of null points. Increasing the photospheric current density in the magnetic configuration does not dramatically change the energy-storage processes within the active region even if the magnetic topology is slightly modified. We conclude that for reasonable values of the photospheric current density (the force-free parameter α<0.25 Mm−1), the magnetic configurations studied do change but not dramatically: i) the original null point stays nearly at the same location, ii) the field-line geometry and connectivity are slightly modified, iii) even if the free magnetic energy is significantly increased, the energy storage happens at the same location. This extensive study of different force-free models for a simple magnetic configuration shows that some topological elements of an observed active region, such as null points, can be reproduced with confidence only by considering the potential-field approximation. This study is a preliminary work aiming at understanding the effects of electric currents generated by characteristic photospheric motions on the structure and evolution of the coronal magnetic field. Title: Explaining observed red and blue-shifts using multi-stranded coronal loops Authors: Regnier, S.; Walsh, R. W.; Pearson, J. Bibcode: 2012decs.confE..39R Altcode: Magnetic plasma loops have been termed the building blocks of the solar atmosphere. However, it must be recognised that if the range of loop structures we can observe do consist of many ''sub-resolution'' elements, then current one-dimensional hydrodynamic models are really only applicable to an individual plasma element or strand. Thus a loop should be viewed is an amalgamation of these strands. They could operate in thermal isolation from one another with a wide range of temperatures occurring across the structural elements. This scenario could occur when the energy release mechanism consists of localised, discrete bursts of energy that are due to small scale reconnection sites within the coronal magnetic field- the nanoflare coronal heating mechanism. These energy bursts occur in a time-dependent manner, distributed along the loop/strand length, giving a heating function that depends on space and time. An important observational discovery with the Hinode/EIS spectrometer is the existence of red and blue-shifts in coronal loops depending on the location of the footpoints (inner or outer parts of the active region), and the temperature of the emission line in which the Doppler shifts are measured. Based on the multi-stranded model developed by Sarkar and Walsh (2008, ApJ, 683, 516), we show that red and blue-shifts exist in different simulated Hinode/EIS passbands: cooler lines (OV-SiVII) being dominated by red-shifts, whilst hotter lines (FeXV-CaXVII) are a combination of both. The distribution of blue-shifts depends on the energy input and not so much on the heating location. Characteristic Doppler shifts generated fit well with observed values. We also simulate the Hinode/EIS rasters to closely compare our simulation with the observations. Even if not statistically significant, loops can have footpoints with opposite Doppler shifts. Title: Internal vs external reconnection observed by SDO in a newly emerged active region Authors: Regnier, S. Bibcode: 2012decs.confE..57R Altcode: The emergence of magnetic fields through the photosphere and the interaction with the coronal environment is an important process allowing the magnetic energy and magnetic helicity to be transported from the convection zone to the solar wind. SDO instruments such as AIA and HMI allow us to study in details the first steps of the emerging process and the thermal structure of the new-born active region. For this study, we combine the SDO/AIA observations at high-cadence in different temperature ranges (from photosphere to the hot corona) with potential field extrapolation of SDO/HMI line-of-sight magnetic field. In particular, we study (i) the interaction of the emerging flux with the coronal environment leading to magnetic reconnection and magnetic pressure enhancement owed to the complex topology of the magnetic field, (ii) the evidence of internal magnetic reconnection within the emerging flux tube whilst crossing the photosphere and expanding into the corona. The later is evidenced by the observation of Ellerman bombs at the chromospheric level and the structuring of the photospheric magnetic field. We thus provide a timeline of the events in the eight hours after the beginning of flux emergence. Title: Modelling the magnetic field evolution with potential fields Authors: Regnier, S. Bibcode: 2011AGUFMSH43B1945R Altcode: The potential field is a quite simple assumption to model the magnetic field of the solar corona as it relies only on the vertical component of the magnetic field measured on the photosphere. However, with the always increasing amount of line-of-sight magnetic field, this assumption is often the best way to approximate the corona magnetic field and to derive useful information on its time evolution. We use SDO/HMI and Hinode/SOT data to study the evolution of quiet-Sun regions and active regions. We focus our study on the magnetic topology of the magnetic configurations, and on the energy budget. We show that the magnetic topology of potential fields is consistent with the observed EUV intensity as observed by SDO/AIA. A quantitative comparison between the EUV emission and magnetic energy density is provided: the relationship between EUV brightenings and magnetic topology is statistically difficult to establish. We also investigate the evolution of the magnetic energy of the potential field related to the activity of the region: the emerging magnetic field and the separation between polarities are mainly responsible for the fluctuation of the magnetic energy budget. Title: A new look at a polar crown cavity as observed by SDO/AIA. Structure and dynamics Authors: Régnier, S.; Walsh, R. W.; Alexander, C. E. Bibcode: 2011A&A...533L...1R Altcode: 2011arXiv1107.3451R Context. The Solar Dynamics Observatory (SDO) was launched in February 2010 and is now providing an unprecedented view of the solar activity at high spatial resolution and high cadence covering a broad range of temperature layers of the atmosphere.
Aims: We aim at defining the structure of a polar crown cavity and describing its evolution during the erupting process.
Methods: We use the high-cadence time series of SDO/AIA observations at 304 Å (50 000 K) and 171 Å (0.6 MK) to determine the structure of the polar crown cavity and its associated plasma, as well as the evolution of the cavity during the different phases of the eruption. We report on the observations recorded on 13 June 2010 located on the north-west limb.
Results: We observe coronal plasma shaped by magnetic field lines with a negative curvature (U-shape) sitting at the bottom of a cavity. The cavity is located just above the polar crown filament material. We thus observe the inner part of the cavity above the filament as depicted in the classical three part coronal mass ejection (CME) model composed of a filament, a cavity, and a CME front. The filament (in this case a polar crown filament) is part of the cavity, and it makes a continuous structuring from the filament to the CME front depicted by concentric ellipses (in a 2D cartoon).
Conclusions: We propose to define a polar crown cavity as a density depletion sitting above denser polar crown filament plasma drained down the cavity by gravity. As part of the polar crown filament, plasma at different temperatures (ranging from 50 000 K to 0.6 MK) is observed at the same location on the cavity dips and sustained by a competition between the gravity and the curvature of magnetic field lines. The eruption of the polar crown cavity as a solid body can be decomposed into two phases: a slow rise at a speed of 0.6 km s-1 and an acceleration phase at a mean speed of 25 km s-1.

Two movies are only available at http://www.aanda.org Title: The UCLan SDO Data Hub Authors: Dalla, S.; Walsh, R. W.; Chapman, S. A.; Marsh, M.; Regnier, S.; Bewsher, D.; Brown, D. S.; Kelly, J.; Laitinen, T.; Alexander, C. Bibcode: 2010AGUFMSH23C1876D Altcode: A data pipeline for the distribution of SDO data products has been developed throughout a number of countries in the US, Europe and Asia. The UK node within this pipeline is at the University of Central Lancashire (UCLan), where a data center has been established to host a rolling AIA and HMI archive, aimed at supplying data to the country's large solar scientific community. This presentation will describe the hardware and software structures of the archive, as well as the best practice identified and feedback received from users of the facility. We will also discuss algorithms that are run locally in order to identify solar features and events. Title: Emergence of an active region with SDO: the first eight hours Authors: Regnier, S. Bibcode: 2010AGUFMSH11A1612R Altcode: We report on the high resolution and high cadence observations of the birth of an active region in a supergranular cell. We use SDO/AIA EUV images to derive the evolution of the thermal properties, and SDO/HMI continuum images and line-of-sight magnetograms to study the time evolution of the magnetic polarities forming a pore. We restrict our study to the first eight hours of the emergence. With the broad temperature coverage of SDO/AIA, we determine the shift in time of appearance of loops in the different EUV channels and compare to the evolution of the photospheric magnetic field. We also observe the evolution of the thermal shielding of the active region with respect to the pre-existing corona. We combine the continuum images and magnetograms to explain the formation of a pore about six hours after the beginning of the flux emergence. Using a time series of potential field extrapolations at full spatial resolution using SDO/HMI magnetograms during the eight hours, we study the change of connectivity and magnetic topology associated with the emergence process: starting from field lines connecting the boundaries of the supergranules in a complex manner, the magnetic field becomes more and more bipolar.We also provide a lower and upper estimate of the magnetic energy inside the active region and therefore of the free magnetic energy that can be released. Title: Modelling the Coronal Magnetic Field Using Hinode (and Future) Data Authors: Wheatland, M. S.; Gilchrist, S. A.; Régnier, S. Bibcode: 2010aogs...21..327W Altcode: There is considerable interest in accurate modelling of the solar coronal magnetic field using photospheric vector magnetograms as boundary data, and the nonlinear force-free model is often used. However, recent studies using Hinode data have demonstrated that this modelling fails in basic ways, with the failure attributable to the departure of the inferred photospheric magnetic field from a force-free state. The solar boundary data are inconsistent with the model, which leads to inconsistencies in calculated force-free solutions. A method for constructing a self-consistent nonlinear force-free solution is described, which identifies a force-free solution that is close to the observed boundary data. Steps towards developing more sophisticated magnetohydrostatic modelling — taking into account pressure and gravitational forces at the level of the solar boundary data — are also outlined. Title: Coronal response to the dynamic evolution of the quiet-Sun magnetic field observed by Hinode/SOT Authors: Regnier, S. Bibcode: 2009AGUFMSH51A1260R Altcode: The new space instrumentation on board the Hinode satellite allows us to study in details the dynamic evolution of the quiet-Sun magnetic field from the photosphere to the corona. Based on high resolution magnetograms Hinode/SOT/SP, we investigate the effects of photospheric motions on the evolution of coronal structures and open field lines. Observed photospheric motions are flux cancellation, coalescence, fragmentation and emergence of polarities. We describe the coronal magnetic field above a quiet-Sun photospheric region as a potential field. We use a time series of 1 hour long with a 1 minute cadence to study the changes in connectivity and magnetic energy of coronal structures subject to these photospheric motions. We especially focus on the redistribution of the magnetic energy density in the corona: a delay of about 2 minutes appears between the photospheric motions and the coronal response. We also demonstrate that the open magnetic flux as a source of the fast solar wind is a tiny fraction of the photospheric flux and stays almost constant over 1 hour. Title: A Self-Consistent Nonlinear Force-Free Solution for a Solar Active Region Magnetic Field Authors: Wheatland, M. S.; Régnier, S. Bibcode: 2009ApJ...700L..88W Altcode: 2009arXiv0906.4414W Nonlinear force-free solutions for the magnetic field in the solar corona constructed using photospheric vector magnetic field boundary data suffer from a basic problem: the observed boundary data are inconsistent with the nonlinear force-free model. Specifically, there are two possible choices of boundary conditions on vertical current provided by the data, and the two choices lead to different force-free solutions. A novel solution to this problem is described. Bayesian probability is used to modify the boundary values on current density, using field-line connectivity information from the two force-free solutions and taking into account uncertainties, so that the boundary data are more consistent with the two nonlinear force-free solutions. This procedure may be iterated until a set of self-consistent boundary data (the solutions for the two choices of boundary conditions are the same) is achieved. The approach is demonstrated to work in application to Hinode/Solar Optical Telescope observations of NOAA active region 10953. Title: Nonlinear Force-Free Magnetic Field Modeling of AR 10953: A Critical Assessment Authors: De Rosa, Marc L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.; Lites, B. W.; Aschwanden, M. J.; Amari, T.; Canou, A.; McTiernan, J. M.; Régnier, S.; Thalmann, J. K.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung, M. C. M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T. Bibcode: 2009SPD....40.3102D Altcode: Nonlinear force-free field (NLFFF) modeling seeks to provide accurate representations of the structure of the magnetic field above solar active regions, from which estimates of physical quantities of interest (e.g., free energy and helicity) can be made. However, the suite of NLFFF algorithms have failed to arrive at consistent solutions when applied to (thus far, two) cases using the highest-available-resolution vector magnetogram data from Hinode/SOT-SP (in the region of the modeling area of interest) and line-of-sight magnetograms from SOHO/MDI (where vector data were not available). One issue is that NLFFF models require consistent, force-free vector magnetic boundary data, and vector magnetogram data sampling the photosphere do not satisfy this requirement. Consequently, several problems have arisen that are believed to affect such modeling efforts. We use AR 10953 to illustrate these problems, namely: (1) some of the far-reaching, current-carrying connections are exterior to the observational field of view, (2) the solution algorithms do not (yet) incorporate the measurement uncertainties in the vector magnetogram data, and/or (3) a better way is needed to account for the Lorentz forces within the layer between the photosphere and coronal base. In light of these issues, we conclude that it remains difficult to derive useful and significant estimates of physical quantities from NLFFF models. Title: A Critical Assessment of Nonlinear Force-Free Field Modeling of the Solar Corona for Active Region 10953 Authors: De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham; Leka, K. D.; Lites, Bruce W.; Aschwanden, Markus J.; Amari, Tahar; Canou, Aurélien; McTiernan, James M.; Régnier, Stéphane; Thalmann, Julia K.; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas; Cheung, Mark C. M.; Conlon, Paul A.; Fuhrmann, Marcel; Inhester, Bernd; Tadesse, Tilaye Bibcode: 2009ApJ...696.1780D Altcode: 2009arXiv0902.1007D Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics, and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically constructed Sun-like test cases, but they are less successful in application to real solar data. Different NLFFF models have been found to have markedly different field line configurations and to provide widely varying estimates of the magnetic free energy in the coronal volume, when applied to solar data. NLFFF models require consistent, force-free vector magnetic boundary data. However, vector magnetogram observations sampling the photosphere, which is dynamic and contains significant Lorentz and buoyancy forces, do not satisfy this requirement, thus creating several major problems for force-free coronal modeling efforts. In this paper, we discuss NLFFF modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT, STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process illustrate three such issues we judge to be critical to the success of NLFFF modeling: (1) vector magnetic field data covering larger areas are needed so that more electric currents associated with the full active regions of interest are measured, (2) the modeling algorithms need a way to accommodate the various uncertainties in the boundary data, and (3) a more realistic physical model is needed to approximate the photosphere-to-corona interface in order to better transform the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of the corona. We make recommendations for future modeling efforts to overcome these as yet unsolved problems. Title: Relationship between photospheric currents and coronal magnetic helicity for force-free bipolar fields Authors: Régnier, S. Bibcode: 2009A&A...497L..17R Altcode: 2009arXiv0903.2697R Aims: The origin and evolution of the magnetic helicity in the solar corona are not well understood. For instance, the magnetic helicity of an active region is often about 1042 Mx2 (1026 Wb2), but the observed processes whereby it is thought to be injected into the corona do not yet provide an accurate estimate of the resulting magnetic helicity budget or time evolution. The variation in magnetic helicity is important for understanding the physics of flares, coronal mass ejections, and their associated magnetic clouds. To shed light on this topic, we investigate here the changes in magnetic helicity due to electric currents in the corona for a single twisted flux tube that may model characteristic coronal structures such as active region filaments, sigmoids, or coronal loops.
Methods: For a bipolar photospheric magnetic field and several distributions of current, we extrapolated the coronal field as a nonlinear force-free field. We then computed the relative magnetic helicity, as well as the self and mutual helicities.
Results: Starting from a magnetic configuration with a moderate amount of current, the amount of magnetic helicity can increase by 2 orders of magnitude when the maximum current strength is increased by a factor of 2. The high sensitivity of magnetic helicity to the current density can partially explain discrepancies between measured values on the photosphere, in the corona, and in magnetic clouds. Our conclusion is that the magnetic helicity strongly depends on both the strength of the current density and also on its distribution.
Conclusions: Only improved measurements of current density at the photospheric level will advance our knowledge of the magnetic helicity content in the solar atmosphere. Title: POLAR investigation of the Sun—POLARIS Authors: Appourchaux, T.; Liewer, P.; Watt, M.; Alexander, D.; Andretta, V.; Auchère, F.; D'Arrigo, P.; Ayon, J.; Corbard, T.; Fineschi, S.; Finsterle, W.; Floyd, L.; Garbe, G.; Gizon, L.; Hassler, D.; Harra, L.; Kosovichev, A.; Leibacher, J.; Leipold, M.; Murphy, N.; Maksimovic, M.; Martinez-Pillet, V.; Matthews, B. S. A.; Mewaldt, R.; Moses, D.; Newmark, J.; Régnier, S.; Schmutz, W.; Socker, D.; Spadaro, D.; Stuttard, M.; Trosseille, C.; Ulrich, R.; Velli, M.; Vourlidas, A.; Wimmer-Schweingruber, C. R.; Zurbuchen, T. Bibcode: 2009ExA....23.1079A Altcode: 2008ExA...tmp...40A; 2008arXiv0805.4389A The POLAR Investigation of the Sun (POLARIS) mission uses a combination of a gravity assist and solar sail propulsion to place a spacecraft in a 0.48 AU circular orbit around the Sun with an inclination of 75° with respect to solar equator. This challenging orbit is made possible by the challenging development of solar sail propulsion. This first extended view of the high-latitude regions of the Sun will enable crucial observations not possible from the ecliptic viewpoint or from Solar Orbiter. While Solar Orbiter would give the first glimpse of the high latitude magnetic field and flows to probe the solar dynamo, it does not have sufficient viewing of the polar regions to achieve POLARIS’s primary objective: determining the relation between the magnetism and dynamics of the Sun’s polar regions and the solar cycle. Title: Nonlinear Force-Free Magnetic Field Modeling of the Solar Corona: A Critical Assessment Authors: De Rosa, M. L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.; Lites, B. W.; Aschwanden, M. J.; McTiernan, J. M.; Régnier, S.; Thalmann, J.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung, M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T. Bibcode: 2008AGUFMSH41A1604D Altcode: Nonlinear force-free field (NLFFF) modeling promises to provide accurate representations of the structure of the magnetic field above solar active regions, from which estimates of physical quantities of interest (e.g., free energy and helicity) can be made. However, the suite of NLFFF algorithms have so far failed to arrive at consistent solutions when applied to cases using the highest-available-resolution vector magnetogram data from Hinode/SOT-SP (in the region of the modeling area of interest) and line-of-sight magnetograms from SOHO/MDI (where vector data were not been available). It is our view that the lack of robust results indicates an endemic problem with the NLFFF modeling process, and that this process will likely continue to fail until (1) more of the far-reaching, current-carrying connections are within the observational field of view, (2) the solution algorithms incorporate the measurement uncertainties in the vector magnetogram data, and/or (3) a better way is found to account for the Lorentz forces within the layer between the photosphere and coronal base. In light of these issues, we conclude that it remains difficult to derive useful and significant estimates of physical quantities from NLFFF models. Title: Coronal Alfvén speeds in an isothermal atmosphere. I. Global properties Authors: Régnier, S.; Priest, E. R.; Hood, A. W. Bibcode: 2008A&A...491..297R Altcode: 2008arXiv0809.1155R Aims: Estimating Alfvén speeds is of interest in modelling the solar corona, studying the coronal heating problem and understanding the initiation and propagation of coronal mass ejections (CMEs).
Methods: We assume here that the corona is in a magnetohydrostatic equilibrium and that, because of the low plasma β, one may decouple the magnetic forces from pressure and gravity. The magnetic field is then described by a force-free field for which we perform a statistical study of the magnetic field strength with height for four different active regions. The plasma along each field line is assumed to be in a hydrostatic equilibrium. As a first approximation, the coronal plasma is assumed to be isothermal with a constant or varying gravity with height. We study a bipolar magnetic field with a ring distribution of currents, and apply this method to four active regions associated with different eruptive events.
Results: By studying the global properties of the magnetic field strength above active regions, we conclude that (i) most of the magnetic flux is localized within 50 Mm of the photosphere; (ii) most of the energy is stored in the corona below 150 Mm; (iii) most of the magnetic field strength decays with height for a nonlinear force-free field slower than for a potential field. The Alfvén speed values in an isothermal atmosphere can vary by two orders of magnitude (up to 100 000 km s-1). The global properties of the Alfvén speed are sensitive to the nature of the magnetic configuration. For an active region with highly twisted flux tubes, the Alfvén speed is significantly increased at the typical height of the twisted flux bundles; in flaring regions, the average Alfvén speeds are above 5000 km s-1 and depart highly from potential field values.
Conclusions: We discuss the implications of this model for the reconnection rate and inflow speed, the coronal plasma β and the Alfvén transit time. Title: What Can we Learn from Nonlinear Force-Free Extrapolations? Authors: Régnier, S. Bibcode: 2008ASPC..397...75R Altcode: Nonlinear force-free extrapolations are used to determine the 3D nature of the coronal magnetic field. The nonlinear force-free fields require knowledge of the vector magnetic field as boundary conditions at the photospheric or chromospheric level. The development of new vector magnetographs such as Hinode/SOT and SDO/HMI will certainly enhance the science that can be done by combining vector field measurements and nonlinear force-free extrapolations. Here, therefore, we summarize our current work on the key properties of a magnetic configuration: geometry, magnetic energy, magnetic helicity, connectivity and magnetic topology. Physical insights deduced from the magnetic configurations are discussed. Title: A new view of quiet-Sun topology from Hinode/SOT Authors: Régnier, S.; Parnell, C. E.; Haynes, A. L. Bibcode: 2008A&A...484L..47R Altcode: 2008arXiv0805.1602R Context: With the recent launch of the Hinode satellite our view of the nature and evolution of quiet-Sun regions has been improved. In light of the new high resolution observations, we revisit the study of the quiet Sun's topological nature.
Aims: Topology is a tool to explain the complexity of the magnetic field, the occurrence of reconnection processes, and the heating of the corona. This Letter aims to give new insights to these different topics.
Methods: Using a high-resolution Hinode/SOT observation of the line-of-sight magnetic field on the photosphere, we calculate the three dimensional magnetic field in the region above assuming a potential field. From the 3D field, we determine the existence of null points in the magnetic configuration.
Results: From this model of a continuous field, we find that the distribution of null points with height is significantly different from that reported in previous studies. In particular, the null points are mainly located above the bottom boundary layer in the photosphere (54%) and in the chromosphere (44%) with only a few null points in the corona (2%). The density of null points (expressed as the ratio of the number of null points to the number of photospheric magnetic fragments) in the solar atmosphere is estimated to be between 3% and 8% depending on the method used to identify the number of magnetic fragments in the observed photosphere.
Conclusions: This study reveals that the heating of the corona by magnetic reconnection at coronal null points is unlikely. Our findings do not rule out the heating of the corona at other topological features. We also report the topological complexity of the chromosphere as strongly suggested by recent observations from Hinode/SOT. Title: Non-Linear Force-Free Field Modeling of a Solar Active Region Around the Time of a Major Flare and Coronal Mass Ejection Authors: De Rosa, M. L.; Schrijver, C. J.; Metcalf, T. R.; Barnes, G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.; Wheatland, M.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann, M.; Kusano, K.; Régnier, S.; Thalmann, J. Bibcode: 2008AGUSMSP31A..06D Altcode: Solar flares and coronal mass ejections are associated with rapid changes in coronal magnetic field connectivity and are powered by the partial dissipation of electrical currents that run through the solar corona. A critical unanswered question is whether the currents involved are induced by the advection along the photosphere of pre-existing atmospheric magnetic flux, or whether these currents are associated with newly emergent flux. We address this problem by applying nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA Active Region 10930 around the time of a powerful X3.4 flare in December 2006. We compute 14 NLFFF models using 4 different codes having a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We do find agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, (3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the ~1032~erg change in energy associated with the coronal electrical currents suffices to power the flare and its associated coronal mass ejection. We discuss the relative merits of these models in a general critique of our present abilities to model the coronal magnetic field based on surface vector field measurements. Title: Nonlinear Force-free Field Modeling of a Solar Active Region around the Time of a Major Flare and Coronal Mass Ejection Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.; Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann, M.; Kusano, K.; Régnier, S.; Thalmann, J. K. Bibcode: 2008ApJ...675.1637S Altcode: 2007arXiv0712.0023S Solar flares and coronal mass ejections are associated with rapid changes in field connectivity and are powered by the partial dissipation of electrical currents in the solar atmosphere. A critical unanswered question is whether the currents involved are induced by the motion of preexisting atmospheric magnetic flux subject to surface plasma flows or whether these currents are associated with the emergence of flux from within the solar convective zone. We address this problem by applying state-of-the-art nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA AR 10930 around the time of a powerful X3.4 flare. We compute 14 NLFFF models with four different codes and a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We discuss the relative merits of these models in a general critique of present abilities to model the coronal magnetic field based on surface vector field measurements. For our application in particular, we find a fair agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, (3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the ~1032 erg change in energy associated with the coronal electrical currents suffices to power the flare and its associated coronal mass ejection. Title: Quiet Sun topology from Hinode/SOT Authors: Regnier, Stephane; Parnell, Clare; Haynes, Andrew Bibcode: 2008cosp...37.2586R Altcode: 2008cosp.meet.2586R The Hinode satellite was launched in 2006 with unprecedented high spatial and temporal resolution revealing the detailed nature of the quiet Sun. Based on the new data recorded by Hinode/SOT, we revisit the magnetic topology of the quiet Sun. It has been found, using point source models, that approximately one null point exists for each source with only 9% of these above the photosphere. In this study, we use a potential field extrapolation from a continuous photospheric magnetic field and analyse the properties of the magnetic nulls. We find that there are few photospheric nulls and most of the null points are located in the chromosphere. Title: Global properties of Alfven speeds in the corona Authors: Regnier, Stephane; Priest, Eric; Hood, Alan Bibcode: 2008cosp...37.2585R Altcode: 2008cosp.meet.2585R We investigate the values and distribution of the Alfvén speed in the solar corona. We assume e that the coronal magnetic field is force-free and the plasma is isothermal and in hydrostatic equilibrium. Firstly we consider a bipolar configuration in order to study the effect of parameters such as the pressure scale-height and the density at the base of the corona. Secondly, we apply the model to four active regions at different stages of their evolution (before and after a flare or a CME). At a given height in the low corona, the Alfvén speed values can vary by two e orders of magnitude (up to 100000 km·s-1 ). For an active region with highly twisted flux tubes, the Alfvén speed is significantly increased at the typical height of the twisted flux bundles; in e flaring regions, the average Alfvén speeds are above 5000 km·s-1 and depart strongly from e potential field values. We discuss implications for coronal heating models and CME models in terms of the plasma β, the inflow speed and the reconnection rate. Title: Influence of boundary conditions on active region topology Authors: Regnier, Stephane Bibcode: 2008cosp...37.2587R Altcode: 2008cosp.meet.2587R The magnetic topology is a key element to understand the physics of solar eruptions. It is well-known that magnetic reconnection leading to the fast release of magnetic energy occurs at topological elements such as null points, separators, quasi-separatrix layers or hyperbolic flux tubes. We investigate the possible change of topology for different models of coronal magnetic fields (potential, linear and nonlinear force-free fields). We consider a solar-like magnetic con- figuration having a null point in the corona under the potential field assumption. Considering currents flowing along field lines slightly modifies the location and nature of the null point. Nevertheless other null points can be created affecting the global topology of the field. Title: Free Magnetic Energy in Solar Active Regions above the Minimum-Energy Relaxed State Authors: Régnier, S.; Priest, E. R. Bibcode: 2007ApJ...669L..53R Altcode: 2008arXiv0805.1619R To understand the physics of solar flares, including the local reorganization of the magnetic field and the acceleration of energetic particles, we have first to estimate the free magnetic energy available for such phenomena, which can be converted into kinetic and thermal energy. The free magnetic energy is the excess energy of a magnetic configuration compared to the minimum-energy state, which is a linear force-free field if the magnetic helicity of the configuration is conserved. We investigate the values of the free magnetic energy estimated from either the excess energy in extrapolated fields or the magnetic virial theorem. For four different active regions, we have reconstructed the nonlinear force-free field and the linear force-free field corresponding to the minimum-energy state. The free magnetic energies are then computed. From the energy budget and the observed magnetic activity in the active region, we conclude that the free energy above the minimum-energy state gives a better estimate and more insights into the flare process than the free energy above the potential field state. Title: Nonlinear force-free models for the solar corona. I. Two active regions with very different structure Authors: Régnier, S.; Priest, E. R. Bibcode: 2007A&A...468..701R Altcode: 2007astro.ph..3756R Context: With the development of new instrumentation providing measurements of solar photospheric vector magnetic fields, we need to develop our understanding of the effects of current density on coronal magnetic field configurations.
Aims: The object is to understand the diverse and complex nature of coronal magnetic fields in active regions using a nonlinear force-free model.
Methods: From the observed photospheric magnetic field we derive the photospheric current density for two active regions: one is a decaying active region with strong currents (AR8151), and the other is a newly emerged active region with weak currents (AR8210). We compare the three-dimensional structure of the magnetic fields for both active region when they are assumed to be either potential or nonlinear force-free. The latter is computed using a Grad-Rubin vector-potential-like numerical scheme. A quantitative comparison is performed in terms of the geometry, the connectivity of field lines, the magnetic energy and the magnetic helicity content.
Results: For the old decaying active region the connectivity and geometry of the nonlinear force-free model include strong twist and strong shear and are very different from the potential model. The twisted flux bundles store magnetic energy and magnetic helicity high in the corona (about 50 Mm). The newly emerged active region has a complex topology and the departure from a potential field is small, but the excess magnetic energy is stored in the low corona and is enough to trigger powerful flares. Title: Nonlinear force-free field extrapolation: numerical methods and applications Authors: Régnier, S. Bibcode: 2007MmSAI..78..126R Altcode: To model 3D coronal magnetic fields, we use different assumptions: the potential field, the linear force-free field and the nonlinear force-free field. The latter assumption requires the knowledge of the three components of the magnetic field at the bottom boundary (photosphere or chromosphere). The recent development of new spectro-polarimetric instruments allows a more accurate and more systematic measurement of the three components of the magnetic field. Before we can make use of the full potential of these instruments, we need to review our knowledge on nonlinear force-free modelling and the solar physics that can be done with those computations. We will summarise the different numerical methods used to determine the coronal magnetic field, and we will review the physical processes and properties derived from the computed magnetic configurations (e.g., magnetic reconnection, energy storage, source of energetic particles). Title: Study of a Small-Scale Eruptive Event Observed by SOHO/SUMER Authors: Tomasz, F.; Régnier, S.; Schwarz, P.; Rybák, J.; Kucera, A.; Heinzel, P.; Curdt, W.; Wöhl Bibcode: 2006ESASP.617E..79T Altcode: 2006soho...17E..79T No abstract at ADS Title: The Dynamics and Structure of the Solar Atmosphere As Obtained from Combined SUMER/SOHO and TIP2/VTT Observations Authors: Tomasz, F.; Régnier, S.; Schwartz, P.; Rybák, J.; Kucera, A.; Heinzel, P.; Curdt, W.; Wöhl Bibcode: 2006ESASP.617E..78T Altcode: 2006soho...17E..78T No abstract at ADS Title: Magnetic Reconnection Process Triggering C-Class Flares in Active Region 8210 Authors: Régnier, S. Bibcode: 2006ESASP.617E.142R Altcode: 2006soho...17E.142R No abstract at ADS Title: Nonlinear Force-Free Modeling of Coronal Magnetic Fields Part I: A Quantitative Comparison of Methods Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Metcalf, Thomas R.; Liu, Yang; McTiernan, Jim; Régnier, Stéphane; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas Bibcode: 2006SoPh..235..161S Altcode: We compare six algorithms for the computation of nonlinear force-free (NLFF) magnetic fields (including optimization, magnetofrictional, Grad-Rubin based, and Green's function-based methods) by evaluating their performance in blind tests on analytical force-free-field models for which boundary conditions are specified either for the entire surface area of a cubic volume or for an extended lower boundary only. Figures of merit are used to compare the input vector field to the resulting model fields. Based on these merit functions, we argue that all algorithms yield NLFF fields that agree best with the input field in the lower central region of the volume, where the field and electrical currents are strongest and the effects of boundary conditions weakest. The NLFF vector fields in the outer domains of the volume depend sensitively on the details of the specified boundary conditions; best agreement is found if the field outside of the model volume is incorporated as part of the model boundary, either as potential field boundaries on the side and top surfaces, or as a potential field in a skirt around the main volume of interest. For input field (B) and modeled field (b), the best method included in our study yields an average relative vector error En = « |B−b|»/« |B|» of only 0.02 when all sides are specified and 0.14 for the case where only the lower boundary is specified, while the total energy in the magnetic field is approximated to within 2%. The models converge towards the central, strong input field at speeds that differ by a factor of one million per iteration step. The fastest-converging, best-performing model for these analytical test cases is the Wheatland, Sturrock, and Roumeliotis (2000) optimization algorithm as implemented by Wiegelmann (2004). Title: Evolution of magnetic fields and energetics of flares in active region 8210 Authors: Régnier, S.; Canfield, R. C. Bibcode: 2006A&A...451..319R Altcode: To better understand eruptive events in the solar corona, we combine sequences of multi-wavelength observations and modelling of the coronal magnetic field of NOAA AR 8210, a highly flare-productive active region. From the photosphere to the corona, the observations give us information about the motion of magnetic elements (photospheric magnetograms), the location of flares (e.g., Hα, EUV or soft X-ray brightenings), and the type of events (Hα blueshift events). Assuming that the evolution of the coronal magnetic field above an active region can be described by successive equilibria, we follow in time the magnetic changes of the 3D nonlinear force-free (nlff) fields reconstructed from a time series of photospheric vector magnetograms. We apply this method to AR 8210 observed on May 1, 1998 between 17:00 UT and 21:40 UT. We identify two types of horizontal photospheric motions that can drive an eruption: a clockwise rotation of the sunspot, and a fast motion of an emerging polarity. The reconstructed nlff coronal fields give us a scenario of the confined flares observed in AR 8210: the slow sunspot rotation enables the occurence of flare by a reconnection process close to a separatrix surface whereas the fast motion is associated with small-scale reconnections but no detectable flaring activity. We also study the injection rates of magnetic energy, Poynting flux and relative magnetic helicity through the photosphere and into the corona. The injection of magnetic energy by transverse photospheric motions is found to be correlated with the storage of energy in the corona and then the release by flaring activity. The magnetic helicity derived from the magnetic field and the vector potential of the nlff configuration is computed in the coronal volume. The magnetic helicity evolution shows that AR 8210 is dominated by the mutual helicity between the closed and potential fields and not by the self helicity of the closed field which characterizes the twist of confined flux bundles. We conclude that for AR 8210 the complex topology is a more important factor than the twist in the eruption process. Title: Evidence of Small Scale Reconnection in a Moving Feature Authors: Régnier, S.; Canfield, R. C. Bibcode: 2005ESASP.600E..94R Altcode: 2005dysu.confE..94R; 2005ESPM...11...94R No abstract at ADS Title: Evolution of the Magnetic Energy Budget in AR 10486 from Potential and Nonlinear Force-Free Models Authors: Régnier, S.; Fleck, B.; Abramenko, V.; Zhang, H. -Q. Bibcode: 2005ESASP.596E..61R Altcode: 2005ccmf.confE..61R No abstract at ADS Title: Describing Coronal Magnetic Fields by Successive Force-Free Equilibia Authors: Régnier, S.; Canfield, R. C. Bibcode: 2005ESASP.596E..13R Altcode: 2005ccmf.confE..13R No abstract at ADS Title: Self and mutual magnetic helicities in coronal magnetic configurations Authors: Régnier, S.; Amari, T.; Canfield, R. C. Bibcode: 2005A&A...442..345R Altcode: Together with the magnetic energy, the magnetic helicity is an important quantity used to describe the nature of a magnetic field configuration. In the following, we propose a new technique to evaluate various components of the total magnetic helicity in the corona for an equilibrium reconstructed magnetic field. The most meaningful value of helicity is the total relative magnetic helicity which describes the linkage of the field lines even if the volume of interest is not bounded by a magnetic surface. In addition if the magnetic field can be decomposed into the sum of a closed field and a reference field (following , Berger 1999 in Magnetic Helicity in Space and Laboratory Plasmas, ed. M. R. Brown, R. C. Canfield, & A. A. Pevtsov, 1), we can introduce three other helicity components: the self helicity of the closed field, the mutual helicity between the closed field and the reference field, and the vacuum helicity (self helicity of the reference field). To understand the meaning of those quantities, we derive them from the potential field (reference) and the force-free field computed with the same boundary conditions for three different cases: a single twisted flux tube derived from the extended Gold-Hoyle solutions, a simple magnetic configuration with three balanced sources and a constant distribution of the force-free parameter, and the AR 8210 magnetic field observed from 17:13 UT to 21:16 UT on May 1, 1998. We analyse the meaning of the self and mutual helicities: the self and mutual helicities correspond to the twist and writhe of confined flux bundles, and the crossing of field lines in the magnetic configuration respectively. The main result is that the magnetic configuration of AR 8210 is dominated by the mutual helicity and not by the self helicity (twist and writhe). Our results also show that although not gauge invariant the vacuum helicity is sensitive to the topological complexity of the reference field. Title: Energetics of AR 0486 from line-of-sight and vector magnetograms Authors: Regnier, S.; Fleck, B. Bibcode: 2005AGUSMSH51C..09R Altcode: Over two weeks in October/November 2003, the Sun featured unusually strong activity, with three large sunspot groups (including the largest one of this solar cycle), twelve X-class flares (including the strongest ever recorded), numerous halo coronal mass ejections (two with near-recorded speeds) and two significant proton storms. Eight of the twelve X-class flares originated from active region AR 10486. To understand the reasons of this peculiar activity, we investigate the evolution of the coronal magnetic field configuration as well as the energetics of AR 10486 before and after the X17.2 flare on October 28. To determine the coronal magnetic fields, we use potential and nonlinear force-free reconstruction techniques using line-of-sight (SOHO/MDI) and vector (MSO/IVM, Huairou, BBSO) magnetograms on the photosphere as boundary conditions. We identify the source region of the flare as related to the existence of null point or separator field line evidenced in a reversed-Y magnetic configuration. From the 3D configurations we derive the magnetic energy budget which can be released during the impulsive phase of the flare. The estimated free magnetic energy is enough to trigger an X-class flare. The continuous evolution of the magnetic energy derived from the potential field extrapolations indicates that the flare does not modify the distribution of magnetic field on the photosphere. We also study the distribution of energy before and after the flare using different vector magnetic field measurements. Title: Self and Mutual Helicities in Coronal Magnetic Configurations Authors: Regnier, S.; Canfield, R. C. Bibcode: 2005AGUSMSP33A..04R Altcode: Together with the magnetic energy, the magnetic helicity is an important quantity used to describe the nature of a magnetic field configuration. The most meaningful value of helicity is the relative magnetic helicity (relative to a reference field) which describes the linkage of the field lines even if the volume of interest is not bounded by a magnetic surface. In addition if the magnetic field can be decomposed into the sum of a closed field and a reference field (following Berger 1999), we can introduce three other helicity values: the self helicity of the closed field, the mutual helicity between the closed field and the reference field, and the vacuum helicity (self helicity of the reference field). To understand the meaning of those quantities, we derive them from the potential field (reference) and the nonlinear force-free field computed with the same boundary conditions for three different cases: (i) a single twisted flux tube derived from the extended Gold-Hoyle solutions, (ii) a simple magnetic configuration with three balanced sources and a constant distribution of the force-free parameter, and (iii) the AR 8210 magnetic field observed at 19:40 UT on May 1, 1998. The self and mutual helicities corresponds to the twist and writhe of confined flux bundles, and the crossing of field lines in the magnetic configuration respectively. The vacuum helicity is interpreted as a measure of the topological complexity of the field. Title: How is Magnetic Energy Stored and Released? Authors: Régnier, S.; Canfield, R. C. Bibcode: 2004ESASP.575..255R Altcode: 2004soho...15..255R No abstract at ADS Title: Magnetic Field Evolution of AR 0486 Before and after the X17 Flare on October 28, 2003 Authors: Régnier, S.; Fleck, B. Bibcode: 2004ESASP.575..519R Altcode: 2004soho...15..519R No abstract at ADS Title: Using Synthetic Emission Images to Constrain Heating Parameters Authors: Lundquist, L. L.; Fisher, G. H.; McTiernan, J. M.; Régnier, S. Bibcode: 2004ESASP.575..306L Altcode: 2004soho...15..306L No abstract at ADS Title: 3D magnetic configuration of the Hα filament and X-ray sigmoid in NOAA AR 8151 Authors: Régnier, S.; Amari, T. Bibcode: 2004A&A...425..345R Altcode: We investigate the structure and relationship of an Hα filament and an X-ray sigmoid observed in active region NOAA 8151. We first examine the presence of such structures in the reconstructed 3D coronal magnetic field obtained from the non-constant-α force-free field hypothesis using a photospheric vector magnetogram (IVM, Mees Solar Observatory). This method allows us to identify several flux systems: a filament (height 30 Mm, aligned with the polarity inversion line (PIL), magnetic field strength at the apex 49 G, number of turns 0.5-0.6), a sigmoid (height 45 Mm, aligned with the PIL, magnetic field strength at the apex 56 G, number of turns 0.5-0.6) and a highly twisted flux tube (height 60 Mm, magnetic field strength at the apex 36 G, number of turns 1.1-1.2). By searching for magnetic dips in the configuration, we identify a filament structure which is in good agreement with the Hα observations. We find that both filament and sigmoidal structures can be described by a long twisted flux tube with a number of turns less than 1 which means that these structures are stable against kinking. The filament and the sigmoid have similar absolute values of α and Jz in the photosphere. However, the electric current density is positive in the filament and negative in the sigmoid: the filament is right-handed whereas the sigmoid is left-handed. This fact can explain the discrepancies between the handedness of magnetic clouds (twisted flux tubes ejected from the Sun) and the handedness of their solar progenitors (twisted flux bundles in the low corona). The mechanism of eruption in AR 8151 is more likely not related to the development of instability in the filament and/or the sigmoid but is associated with the existence of the highly twisted flux tube (∼1.1-1.2 turns). Title: ILCT: Recovering Photospheric Velocities from Magnetograms by Combining the Induction Equation with Local Correlation Tracking Authors: Welsch, B. T.; Fisher, G. H.; Abbett, W. P.; Regnier, S. Bibcode: 2004ApJ...610.1148W Altcode: We present three methods for deriving the velocity field in magnetized regions of the Sun's photosphere. As a preliminary step, we introduce a Fourier-based local correlation tracking (LCT) routine that we term ``FLCT.'' By explicitly employing the observation made by Démoulin & Berger, that results determined by LCT applied to magnetograms involve a combination of all components of the velocity and magnetic fields, we show that a three-component velocity field can be derived, in a method we term algebraic decomposition, or ADC. Finally, we introduce ILCT, a method that enforces consistency between the normal component of the induction equation and results obtained from LCT. When used with photospheric vector magnetograms, ILCT determines a three-component photospheric velocity field suitable for use with time sequences of such magnetograms to drive boundary conditions for MHD simulations of the solar corona. We present results from these methods applied to vector magnetograms of NOAA AR 8210 on 1998 May 1. Title: The Magnetic Field Evolution of AR 10486 and AR 10488 Before and After the X17 Flare on Oct. 28, 2003 Authors: Regnier, S.; Fleck, B. Bibcode: 2004AAS...204.0205R Altcode: 2004BAAS...36..668R We investigate the causes and the consequences of the X17 flare which occured in active region (AR) 10486 on Oct. 28, 2003. Using MDI high-cadence longitudinal magnetograms, we first follow the evolution of the photospheric magnetic field of both AR 10486 (site of the flare) and AR 10488 (new emerged active region). We then identify the main photospheric motions in AR 10486 which are precursors of the eruptive phenomena (e.g., emergence of flux, cancellation of flux). We also focus our study on the fast emergence of AR 10488 and the change of connectivity between the two active regions after the flare.

We also study the evolution of the coronal magnetic fields assuming a potential field equilibrium state. This is a case study to know if we can forecast a solar eruption using a time series of potential field extrapolations.

For both active regions, an IVM vector magnetogram is available almost 16 hours before the flare and is used as a snapshot. Those two magnetograms allow us to determine the nonlinear force-free magnetic configurations as well as the free energy budgets. These computations allow us to estimate how far those active regions are from the potential field configurations.

S. Regnier's research is funded by the European Community's Human Potential Programme through the European Solar Magnetism Network (contract HPRN-CT-2002-00313). Title: Steady State Energy Balance in the Solar Corona Authors: Lundquist, L. L.; Fisher, G. H.; McTiernan, J. M.; Regnier, S. Bibcode: 2004AAS...204.7308L Altcode: 2004BAAS...36Q.801L We have developed a steady-state energy balance model of the solar corona, which calculates coronal magnetic field structure and thermodynamics from a photospheric magnetogram. The method involves solving an energy equation along individual coronal loops, allowing for flows, gravity, non-uniform heating, and cross-sectional area variations. The calculated emissivities are then interpolated to a 3-d grid and used to create synthetic X-ray and EUV emission images. Comparing observed coronal images from satellite data with theoretical images generated using different assumptions about the heating term can yield observational constraints on coronal heating mechanisms. This work was supported by a DoD/AFOSR MURI grant, ``Understanding Magnetic Eruptions and their Interplanetary Consequences." Title: ILCT: Combining Local Correlation Tracking with the Magnetic Induction Equation Authors: Fisher, G. H.; Welsch, B. T.; Abbett, W. P.; Regnier, S. Bibcode: 2004AAS...204.8805F Altcode: 2004BAAS...36..820F In order to use sequences of vector magnetogram data as input to MHD simulations of the solar atmosphere, one must ensure that the data is consistent with the MHD induction equation. We describe a new technique, ILCT, that uses local correlation tracking to determine a 3-D flow field that is consistent with the ideal MHD induction equation. The flow fields are thus suitable for incorporation into the photospheric boundary of an MHD simulation of the solar atmosphere. Title: Magnetic energy and magnetic helicity budget in AR 8210: What are the sources of flaring activity? Authors: Régnier, S.; Canfield, R. C. Bibcode: 2004IAUS..223..297R Altcode: 2005IAUS..223..297R The active region 8210 (AR 8210) observed on May 1, 1998 is the site of numerous flares. By studying a time series (from 17:00 UT to 21:40 UT) of reconstructed coronal magnetic configurations, we give a scenario of the eruptive phenomena in AR 8210 involving the rotation of the sunspot and the complex topology in a reconnection process. We also study the time evolution of the energy and of the helicity budget. We compute the free energy in the corona, the magnetic energy rate due to transverse photospheric motions. We conclude that the photospheric motions are related to flaring activities and occur before the injections of energy into the corona. In terms of magnetic helicity, we are able to derived the relative magnetic helicity (relative to the potential field) and the helicity of the potential field configuration. The vacuum helicity (or helicity of the potential field) is constant during the time period and characterizes the complex topology. For this time period, the relative magnetic helicity does not show obvious changes related to the flaring activity. Title: The Active Region 8210: Observations, Coronal Magnetic Fields and Energetics Authors: Regnier, S.; Canfield, R. C. Bibcode: 2003AGUFMSH22A0174R Altcode: The active region 8210 observed on May 1, 1998 is the site of several flares (3 C-class flares from 17:00 UT to 22:00 UT and one M-class flare at 22:40 UT). In this study, we analyse the causes and consequences of these flares inside the coronal magnetic configurations: sunspot rotation, moving features, cancellation of flux. The time evolution of AR 8210 from observations (magnetograms, Hα , EUV, Soft X-rays) and the nonlinear force-free reconstructed magnetic fields reveals that the sites of activity are related to the topological skeleton (null points, separatrix surfaces, separators): field lines crossing a separatrix surface reconnect in an other connectivity domain and produce an Hα brightening at the footpoints. We also determine the free magnetic energy budget (difference between nonlinear and potential field magnetic energy) and the relative magnetic helicity. The photospheric increase (or decrease) of magnetic flux is related to the evolution of the magnetic energy in the corona above the active region as well as to the occurence of flares. The main photospheric changes occur between the times of flaring activity. AR 8210 is a case study for the Solar MURI project. Title: Temperature, Density, and Magnetic Field Reconstructions of Active Region Coronae Authors: Lundquist, L. L.; Fisher, G. H.; Régnier, S.; Liu, Y.; Abbett, W. P. Bibcode: 2003AGUFMSH42B0509L Altcode: We present simulated coronal emission pictures of some case-study solar active regions, including NOAA-designated regions 8210 and 8038. The simulated emissions are calculated from a 3-d temperature, density, and magnetic field model of the corona based on first principles. The method involves a static energy balance along individual coronal loops, with the heating term taken from a given coronal heating theory. The predicted emissions can be compared with observed X-ray and UV satellite images. By comparing the predictions of various heating theories with observations, we can determine constraints on the probable mechanisms of coronal heating. The model is also useful for a variety of other applications, such as testing of coronal magnetic field extrapolation techniques, calculations of wave propagation and shock phenomena, and testing assumptions about the spatial distribution of heating along loops. This work was supported by a DoD/AFOSR MURI grant, "Understanding Magnetic Eruptions and their Interplanetary Consequences." Title: Detection of diluted marine tertiary tephra by electron spin resonance and magnetic measurements Authors: Ananou, B.; Regnier, S.; Ksari, Y.; Marfaing, J.; Stepanov, A.; Touchard, Y.; Rochette, P. Bibcode: 2003GeoJI.155..341A Altcode: Oligocene sediments from ODP leg 115 (South Indian Ocean), Site 709 and Site 711, have been investigated using electron spin resonance (ESR) and magnetic susceptibility measurements, to detect volcanic tephra layers of supposed Ethiopian traps origin. The results obtained at room temperature, without separating the volcanic material from the bulk sediment, show that the ash-content strongly influences the lineshape and intensity of the ESR signal. As a result, the ESR alone, can be used as a powerful tool for characterizing the diluted ash-content of marine sediments. We have also found a strong similarity between the ESR spectra of the same tephra layers from the two sites. Title: A Temperature and Density Model of the Solar Corona Authors: Lundquist, L. L.; Regnier, S.; Abbett, W. P.; Fisher, G. H. Bibcode: 2003SPD....34.0404L Altcode: 2003BAAS...35..811L We have developed the foundations of a 3-d global temperature and density model of the solar corona based on first principles. The method involves a static energy balance along individual coronal loops, with the heating term taken from a given coronal heating theory. We use the model to create synthetic emission images of active regions for comparison with observed X-ray and UV satellite images. The technique will enable us to perform a statistical study of active region heating with Yohkoh data from the last decade, comparing observations with the predicted emission measures and X-ray morphologies for different heating theories. The model is also useful for a variety of other applications, such as calculations of wave propagation and shock phenomena, testing of coronal magnetic field extrapolation techniques such as the potential and FFF models, and testing assumptions about the spatial distribution of heating along loops.

We have applied the technique to two cases: a simulated emerged active region, and NOAA active region 8210. These cases employ a heating term derived from the empirical relationship of Pevtsov et al. (2003) relating soft X-ray luminosity to total unsigned magnetic flux for a wide range of solar and stellar magnetic features. We present results from these two cases, including a comparison of the synthetic emission images of AR 8210 with Yohkoh SXT data. This work was supported by a DoD/AFOSR MURI grant, "Understanding Magnetic Eruptions and their Interplanetary Consequences." Title: Force-free Fields in Active Regions: Magnetic configurations and Energetics Authors: Regnier, S.; Canfield, R. C.; Amari, T. Bibcode: 2003SPD....34.0103R Altcode: 2003BAAS...35..805R To determine the 3D configuration of solar active regions and to define boundary conditions for MHD codes, we reconstruct the coronal magnetic field from photospheric measurements. For that, we consider the active region in an equilibrium state. Three hypotheses are then often used: the potential field (no electric current), the linear force-free field (the current density is α times the magnetic field, α is a constant), the nonlinear force-free field (α is a function of space). We here compare those three models in terms of connectivity changes and energetics for two different active regions: AR 8151 and AR 8210. AR 8151 shows dramatical changes between these models whereas AR 8210 configuration stays close to the potential field. The structure of the filament and of the sigmoid observed in AR 8151 can only be determined in the nonlinear force-free field: both structures are identified with twisted flux tubes with ∼ 0.5-0.6 turns. Interestingly, the filament is a right-handed structure whereas the sigmoid is left-handed! This work is a part of the Solar MURI project. Title: MHD waves in active region filament from SOHO-THEMIS joint observations Authors: Régnier, S.; Solomon, J.; Vial, J. C.; Mein, P. Bibcode: 2002ESASP.505..647R Altcode: 2002IAUCo.188..647R; 2002solm.conf..647R The stability of solar filaments and their implications for eruptive events can be revealed by the existence of magnetohydrodynamic (MHD) waves. During the MEDOC campaign on May 2000, we performed joint observations involving SOHO and THEMIS instruments (CDS and MSDP respectively). We analyse the modes of oscillations for several spectral lines (Hα at 6563 Å, He I at 584 Å and Mg X at 609 Å): intermediate (6-40 min) and short (< 5 min) periods are found and are discusssed in terms of MHD waves. The Hα time series (MSDP) in both line center intensity and line-of-sight Doppler shifts provide constraints on models of filament oscillations. Title: Non-constant-α force-free field of active region NOAA 8210 Authors: Régnier, S.; Amari, T.; Canfield, R. C. Bibcode: 2002ESASP.505...65R Altcode: 2002IAUCo.188...65R; 2002solm.conf...65R We investigate the 3D coronal magnetic configuration of the active region NOAA 8210 (AR8210). This active region observed on May 1, 1998 is the site of numerous flares. Using the non-constant-α force-free hypothesis, we determine the coronal magnetic field of AR8210. The EIT/SOHO observations and the reconstructed magnetic configuration suggest that the initiation of the eruptive events is related to the existence of a complex topology (e.g. separatrix surfaces). From some characteristic parameters before and after the eruptions, we note that the magnetic energy (the free magnetic budget) decreases by 28% (55%, respectively). Title: 3D Coronal magnetic field from vector magnetograms: non-constant-alpha force-free configuration of the active region NOAA 8151 Authors: Régnier, S.; Amari, T.; Kersalé, E. Bibcode: 2002A&A...392.1119R Altcode: The Active Region 8151 (AR 8151) observed in February 1998 is the site of an eruptive event associated with a filament and a S-shaped structure, and producing a slow Coronal Mass Ejection (CME). In order to determine how the CME occurs, we compute the 3D coronal magnetic field and we derive some relevant parameters such as the free magnetic energy and the relative magnetic helicity. The 3D magnetic configuration is reconstructed from photospheric magnetic magnetograms (IVM, Mees Solar Observatory) in the case of a non-constant-alpha force-free (nlff) field model. The reconstruction method is divided into three main steps: the analysis of vector magnetograms (transverse fields, vertical density of electric current, ambiguity of 180deg), the numerical scheme for the nlff magnetic field, the interpretation of the computed magnetic field with respect to the observations. For AR 8151, the nlff field matches the coronal observations from EIT/SOHO and from SXT/Yohkoh. In particular, three characteristic flux tubes are shown: a highly twisted flux tube, a long twisted flux tube and a quasi-potential flux tube. The maximum energy budget is estimated to 2.6*E31 erg and the relative magnetic helicity to 4.7*E34 G2 cm4. From the simple photospheric magnetic distribution and the evidence of highly twisted flux tubes, we argue that the flux rope model is the most likely to describe the initiation mechanism of the eruptive event associated with AR 8151. Title: Non-constant-alpha force-free reconstruction of the coronal magnetic field. Example of the active region NOAA 8151 Authors: Regnier, S.; AMARI, T.; Kersale, E. Bibcode: 2001AGUFMSH11C0729R Altcode: We present the method and results of a non-constant-alpha force-free reconstruction of the 3D coronal magnetic field of an active region. AR 8151 observed in February 1998 exhibits a filament, a system of coronal loops, and a sigmoid. In order to determine the magnetic configuration of such structures, a non-constant-alpha force-free method (Amari et al 1997, Solar Physics 174, 129) is used to reconstruct the coronal magnetic field using the photospheric vector magnetograms as boundary condition. We compare the geometric and the topological changes in the magnetic configurations given by the three following methods: current-free field, constant-alpha force-free field and non-constant-alpha force-free field. The comparison between the observations (SXT/Yohkoh, EIT/SOHO) and the three models confirms that the non-constant-alpha force-free field matches the observations. In particular, the sigmoid can be reproduced by twisted flux tubes with a height of 40,000 or 60,000 km, and the system of coronal loops is well described by an untwisted flux tube (40,000 km). We also look for the magnetic dips which are combined with the filament material. The possible magnetic configurations for supporting the filament are either a quadrupolar magnetic field or a long twisted flux tube. From the chromospheric and magnetic observations, we conclude that the most likely configuration is the long twisted flux tube with a height of 30,000 km. In summary, with the non-constant-alpha force-free field we are able to reconstruct the coronal magnetic structures such as the system of coronal loops and the sigmoid, and to determine the structure of the magnetic field lines supporting the filament material. Title: Oscillations in an active region filament: Observations and comparison with MHD waves Authors: Régnier, S.; Solomon, J.; Vial, J. C. Bibcode: 2001A&A...376..292R Altcode: During the MEDOC Campaign 4, on October 1999, observations of a solar active region filament were carried out by the SUMER/SoHO spectrometer. A time sequence of this filament has been obtained with a duration of 7 h 30 min and with a temporal resolution of 30 s. The Fourier analysis of the line-of-sight Doppler velocities measured in the 584.33 Å HeI line allows us to detect oscillations in several ranges of periodicities (short periods: less than 5 min, intermediate periods: 6-20 min, and long periods: greater than 40 min). From a theoretical point of view, we consider the possible modes of oscillations of an active region filament. Following \cite{joa93a}, we treat the filament as a plasma slab embedded in a uniform magnetic field inclined at an angle phi to the long axis of the slab. Solving the dispersion equations for Alfvén waves and magnetoacoustic waves, primary and secondary mode frequencies appear to be non-equidistant. For the comparison between the observed and calculated frequencies, we outline an identification method of the oscillation modes in the observed filament. This identification provides a diagnostic of the filament: the angle between the magnetic field and the long axis of the slab is estimated to be 18deg, and the magnetic field strength B (G) is proportional to the square root of the density rhoo (cm-3) in the slab, B ~ 2.9 x 10-5 sqrt {rhoo}. Title: Reconstruction of the Coronal Magnetic Field for Active Region NOAA 8151 Authors: Régnier, S.; Amari, T. Bibcode: 2001IAUS..203..441R Altcode: No abstract at ADS Title: SUMER/SOHO Observations of Long Period Oscillations in an Active Region Filament Authors: Régnier, S.; Solomon, J.; Vial, J. C. Bibcode: 2001IAUS..203..307R Altcode: During the MEDOC campaign #4 (October 1999), we observed an active region filament with the SUMER/SoHO spectrometer. After a global description of the active region NOAA 8725 with several instruments on board SoHO, we present a Fourier analysis of SUMER long time observations. This analysis allows to detect oscillations in several ranges of periodicities : 6-20 min, 30-40 min, and 55-150 min. We discuss these periodicities in terms of Alfvén and magnetoacoustic waves obtained in filament models developped by different authors. New MEDOC campaign (May 2000) coordinated with THEMIS (Tenerife) observatory should allow to examine the problem more closely. Title: Magnetic and Dynamic Evolution of an Active Region Authors: Régnier, S.; Solomon, J.; Vial, J. C.; Amari, T.; Mickey, D. Bibcode: 1999ESASP.448..519R Altcode: 1999mfsp.conf..519R; 1999ESPM....9..519R No abstract at ADS Title: Multi-Instrument Study Of The Evolution Of An Active Region Authors: Regnier, S.; Amari, T.; Solomon, J.; Vial, J. C.; Mickey, D. Bibcode: 1999ESASP.446..571R Altcode: 1999soho....8..571R We follow, for about half a solar rotation, the dynamic evolution of an acive region (AR 8151) which exhibited a single heading sunspot and a more diffuse following magnetic flux and a filament eruption on 12 February 1998 at 13:51. For longitudinal magnetic observations, we use the MDI (SoHO) magnetograph and for vector magnetic fields the IVM (Mees Solar Observatory, Hawaii). The dynamic evolution is derived from time-sequence images in the Fe XII line (195 Angstrom) from EIT (SoHO). Density and abundance diagnostic of the filament are obtained from SoHO spectrometers (CDS, SUMER). Title: Microrobotique : modèle dynamique et loi horaire pour une micromanipulation par adhesion Authors: Rollot, Y.; Regnier, S.; Guinot, J. Bibcode: 1998CRASB.326..469R Altcode: The emergence of new microtechnologies to be used in micro-world applications raises an increasing interest in micro-scale manipulations. 3D assembling of micro-machines by means of contacts and bonds between pieces of different materials and geometries is an example of the new challenge in micro-systems. Micro-scale manipulations imply a knowledge and control of micro-contact mechanics phenomena. Our aim is to understand the mechanical phenomenon at the micro-scale level, to anticipate the manipulation by increasing or decreasing the sticking effect and to define and develop new manipulation skills using adhesion. Thus, a dynamic model of a micro-manipulation is presented and some simulations are discussed. Title: Statistical analysis of solar bright points observed with the SOHO spacecraft. Authors: Régnier, S.; Bocchialini, K.; Vial, J. -C.; Delaboudinière, J. -P.; Thompson, W. Bibcode: 1998CRASB.326..211R Altcode: 1998CR2...326..211R Bright points, small and short lifetime structures, appear permanently in the atmosphere and could be associated with magnetic reconnections, potential sources of coronal heating. Such structures have been observed with the coronal instruments on-board SOHO and a statistical analysis was carried out in order to find the signature of very small scale structures. Title: Extraterrestrial Evidence Regarding the Frequency of Collisional Events in the Solar System Authors: Lavielle, B.; Regnier, S.; Simonoff, G. N.; Marti, K.; Woodard, M. Bibcode: 1985Metic..20Q.692L Altcode: No abstract at ADS Title: Exposure ages of iron meteorites: Complex histories and the constancy of galactic cosmic rays Authors: Lavielle, B.; Marti, K.; Regnier, S. Bibcode: 1985irss.rept...15L Altcode: Starting from a compilation of measured cosmogenic He, Ne, Ar, and K isotopes in iron meteorites, an exposure age T38 is defined. This age is found useful to study the exposure history of iron meteorites in terms of complex history, age distribution versus time and group, and galactic cosmic ray constancy or not. Exposure ages of less than 200 million yr can be determined. Title: On the Record of Galactic Cosmic Ray Flux and Exposure Histories of Iron Meteorites Authors: Regnier, S.; Lavielle, B.; Marti, K.; Simonoff, G. N. Bibcode: 1984Metic..19..298R Altcode: No abstract at ADS Title: Cosmic ray exposure ages of iron meteorites, complex irradiation and the constancy of cosmic ray flux in the past. Authors: Marti, K.; Lavielle, B.; Regnier, S. Bibcode: 1984LPICo.526...25M Altcode: While previous calculations of potassium ages assumed a constant cosmic ray flux and a single stage (no change in size) exposure of iron meteorites, present calculations relaxed these constancy assumptions and the results reveal multistage irradiations for some 25% of the meteorites studied, implying multiple breakup in space. The distribution of exposure ages suggests several major collisions (based on chemical composition and structure), although the calibration of age scales is not yet complete. It is concluded that shielding-corrected (corrections which depend on size and position of sample) production rates are consistent for the age bracket of 300 to 900 years. These production rates differ in a systematic way from those calculated for present day fluxes of cosmic rays (such as obtained for the last few million years). Title: Cosmic Ray Exposure Ages of Iron Meteorites, Complex Irradiation and the Constancy of Cosmic Ray Flux in the Past Authors: Marti, K.; Lavielle, B.; Regnier, S. Bibcode: 1984LPI....15..511M Altcode: No abstract at ADS Title: On the record of galactic cosmic ray flux and traffic break-ups in iron meteorites Authors: Regnier, S.; Lavielle, B.; Marti, K.; Simonoff, G. N. Bibcode: 1984LPICo.537E..53R Altcode: No abstract at ADS Title: Measurement of cross sections for 22Na, 20-22Ne and 36-42Ar in the spallation of Mg, Al, Si, Ca and Fe. Production ratios of some cosmogenic nuclidesin meteorites. Authors: Baros, F.; Regnier, S. Bibcode: 1984JPhys..45..855B Altcode: No abstract at ADS Title: 22Na/22Ne and 26Al/21Ne Production Ratios in Iron Meteorites Authors: Regnier, S.; Baros, F.; Lavielle, B.; Simonoff, G. N. Bibcode: 1983Metic..18Q.384R Altcode: No abstract at ADS Title: About Cosmogenic Krypton in Iron Meteorites Authors: Lavielle, B.; Regnier, S. Bibcode: 1983Metic..18R.335L Altcode: No abstract at ADS Title: More About Cosmogenic Krypton Authors: Regnier, S.; Lavielle, B.; Simonoff, G. N. Bibcode: 1982Metic..17..273R Altcode: No abstract at ADS Title: On the Production Ratio of Some Pairs of Isotopes in Meteorites Authors: Regnier, S.; Baros, F. Bibcode: 1982Metic..17Q.274R Altcode: No abstract at ADS Title: Nuclear reactions in Rb, Sr, Y, and Zr targets Authors: Regnier, S.; Lavielle, B.; Simonoff, M.; Simonoff, G. N. Bibcode: 1982PhRvC..26..931R Altcode: Excitation functions of all stable or long-lived krypton isotopes were measured or estimated for incident protons and neutrons in Rb, Sr, Y, and Zr targets. Experimental data concern mostly Y and Zr targets bombarded with 0.059 to 24 GeV protons. The products 78-86Kr, 74As, 75Se, 83,84,86Rb, 85Sr, 88Y, 88,95Zr, and 92Nbm were measured using high-sensitivity mass spectrometry and nondestructive γ counting. Lighter products such as 38,39,42Ar and 12 radioactive isotopes from 7Be to 65Zn were also measured in some cases and their cross sections are given in an appendix. Most excitation functions pass through a maximum between 0.4 and 0.8 GeV, and the peak energy could depend on the ΔA value. The results, combined with a general survey of nuclear reactions in Ga to Nb targets, permitted the development of new systematics leading to the calculation of spallation-produced Kr isotopes in the moon bombarded with galactic and solar cosmic rays. Compared to cosmogenic krypton measured in nine well-documented lunar samples, 83Kr is predicted with a precision better than 33% (1σ) and the production ratios iKr/83Kr are predicted to better than 25%. It is concluded that the cosmogenic ratios 86Kr/83Kr and 81Kr/83Kr are dependent on the main target element concentrations. This should be taken into account in strontium-rich samples when calculating exposure ages of extraterrestrial materials. NUCLEAR REACTIONS 89Y and Zr, (p, spallation) E=0.059-24 GeV; measured σ(E) for 78-86Kr and 12 radioactive products. Systematics of p- and n-induced reactions in Rb, Sr, Y, and Zr. Cosmogenic krypton. Title: Spallation of Sr, Y and Zr Targets and Cosmogenic Krypton Authors: Regnier, S.; Lavielle, B.; Simonoff, M.; Simonoff, G. N. Bibcode: 1981Metic..16R.382R Altcode: No abstract at ADS Title: Cosmic ray exposure ages of chondrites, pre-irradiation and constancy of cosmic ray flux in the past Authors: Nishiizumi, K.; Regnier, S.; Marti, K. Bibcode: 1980E&PSL..50..156N Altcode: A systematic calibration of the production rate of one specific cosmic-ray-produced nuclide in chondrites, that of 21Ne, was achieved by using four independent methods: P 21(1.11) = 0.507 ± 0.039, 0.302 ± 0.013, 0.312 ± 0.017and0.292 ± 0.019 (in units of 10 -8 cm 3 STP/g My) based on 26Al-age, 53Mn-age, 81Kr- 83Kr and 22Na- 22Ne methods, respectively. These production rates are all normalized to a shielding parameter ratio 22Ne/ 21Ne= 1.11 and to the chemical composition of L chondrites. The results obtained by the latter three methods are in good agreement, but they disagree in a systematic way with the 26Al-age calibration. Based on these results, we recommend a value P 21(1.11) = 0.31 and a production rate equation:P 21 = 4.845 P 21 (1.11) F[21.77( 22Ne/ 21Ne) - 19.32] -, where F = 1.00 for L and LL, and F = 0.93 for H chondrites, for the calculation of cosmic ray exposure ages on the basis of Ne concentrations. In an attempt to assess possible causes for this discrepancy, we discuss the 26Al half-life measurements, we evaluate effects resulting from pre-irradiation of meteorites, and we discuss the evidence regarding the constancy of the cosmic ray flux in the past, in the light of some recent astronomical observations. Title: Cosmic Ray Exposure Ages of Meteorites: A Recalibration Authors: Nishiizumi, K.; Regnier, S.; Marti, K. Bibcode: 1979Metic..14..499N Altcode: No abstract at ADS Title: Pu-Nd-Xe Dating: A Stepwise Approach Authors: Marti, K.; Kurtz, J. P.; Regnier, S. Bibcode: 1979Metic..14R.482M Altcode: No abstract at ADS Title: Production of argon isotopes by spallation of Sc, Ti, Fe, Co, Ni, and Cu Authors: Regnier, S. Bibcode: 1979PhRvC..20.1517R Altcode: Spallation ratios and production cross sections of 36,38,39,42Ar have been measured for the interaction of 0.080, 0.150, 0.600, 1.05, and 24 GeV protons with scandium, titanium, iron, cobalt, nickel, and copper. Argon is measured by means of a 60° 12 cm radius mass spectrometer, equipped with a gas extraction line and a calibration system. Precision is 1 to 5% for isotope ratios, and 10 to 20% for the cross sections. With regard to spallation reactions, some systematic effects are shown or confirmed. Excitation functions go through a maximum at high energy, then drop asymptotically to a constant value. The ratio of maximum to asymptote cross sections is about 1.6. The spallation ratios depend linearly on the (NZ)T ratios of the target and there is probably a linear correlation between the position of the peak of the spallation distribution and the (NZ)T ratio. Experimental values are compared with semiempirical fits and some astrophysical implications are discussed. NUCLEAR REACTIONS Spallation; targets Sc, Ti, Fe, Co, Ni, Cu; protons 0.080, 0.150, 0.600, 1.05, 24 GeV; measured σ for formation of 36, 38, 39, 42Ar; mass spectrometry; σ compared with semiempirical calculations; astrophysical implications. Title: Predicted Versus Observed Cosmic-Ray Produced Noble Gases in Lunar Samples: Improved KR Production Ratios Authors: Regnier, S.; Hohenberg, C. M.; Marti, K.; Reedy, R. C. Bibcode: 1979LPI....10.1016R Altcode: No abstract at ADS Title: Noble Gass Trapping during Condensation: a Laboratory Study Authors: Kothari, B. K.; Marti, K.; Niemeyer, S.; Regnier, S.; Stephens, J. R. Bibcode: 1979LPI....10..682K Altcode: No abstract at ADS Title: Production of KR Isotopes by Spallation on Y Targets and Implications for Kr-Kr Dating Authors: Regnier, S. Bibcode: 1979LPI....10.1013R Altcode: No abstract at ADS Title: Predicted versus observed cosmic-ray-produced noble gases in lunar samples: improved Kr production ratios. Authors: Regnier, S.; Hohenberg, C. M.; Marti, K.; Reedy, R. C. Bibcode: 1979LPSC...10.1565R Altcode: New sets of cross sections for the production of krypton isotopes from targets of Rb, Sr, Y, and Zr have been constructed primarily on the bases of experimental excitation functions for Kr production from Y. These cross sections were used to calculate galactic-cosmic-ray and solar-proton production rates for Kr isotopes in the moon. The paper reports spallation Kr data obtained from ilmenite separates of rocks 10017 and 10047. Production rates and isotopic ratios for cosmogenic Kr observed in ten well-documented lunar samples and in ilmenite separates and bulk samples from several lunar rocks with long but unknown irradiation histories were compared with predicted rates and ratios. The agreements were generally quite good. Title: Cosmic Ray Exposure Ages: An Assessment Authors: Marti, K.; Regnier, S. Bibcode: 1978Metic..13..551M Altcode: No abstract at ADS Title: Cross Section Measurements for Production of Stable Isotopes of Ne and Ar by High-Energy Spallation of Al, Sc, Ti, Fe, Co, Ni and Cu Authors: Regnier, S. Bibcode: 1977ICRC....2...76R Altcode: 1977ICRC...15b..76R; 1978ICRC....2...76R Some 100 cross sections are reported for the spallation production of Ne-20, Ne-21, Ne-22, Ar-36, Ar-38, Ar-39, and Ar-42 in Al, Sc, Ti, Fe, Co, Ni, and Cu targets bombarded with protons having energies of 0.080, 0.150, 0.600, 1.05, and 24.0 GeV. The results are shown to be in good agreement with the two-step (cascade-evaporation) model of Serber (1947) and to confirm the existence of appreciable variations of the spallation-reaction cross sections for incident energies greater than 1 GeV. It is concluded that these variations must be taken into account in the analysis of observational results on cosmic-ray composition. Title: Cl36 and the age of the cosmic rays. Authors: Cassé, M.; Goret, P.; Regnier, S. Bibcode: 1975ICRC....2..544C Altcode: No abstract at ADS Title: Production de béryllium-7 dans le fer et le silicium par des protons de 0.6 et 24 GeV. Authors: Regnier, S.; Paillard, P.; Simonoff, G. Bibcode: 1975CRASB.280..513R Altcode: No abstract at ADS Title: Production de 26Al dans Fe et St par protons de 0.6 et 24 GeV Authors: Regnier, S.; Lagarde, M.; Simonoff, G. N.; Yokoyama, Y. Bibcode: 1973E&PSL..18....9R Altcode: Cross sections for 26Al formation in iron and silicon targets bombarded with 0.6 and 24 GeV protons have been measured by using highly selective chemical separation and γ-γ spectrometry. The cross sections for iron are in mb: 0.4 ± 0.1 at 0.6 GeV, 2.5 ± 0.4 at 24 GeV; for silicon 12.6 ± 1.9 at 0.6 GeV, 6.4 ± 1.4 at 24 GeV. These values are used in order to fit the excitation function Fe(p,X) 26Al, of great astrophysical interest, by analogy with known equivalent nuclear reactions.