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Author name code: regnier
ADS astronomy entries on 2022-09-14
author:"Regnier, Stephane"
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Title: The Independence of Oscillatory Reconnection Periodicity from
the Initial Pulse
Authors: Karampelas, Konstantinos; McLaughlin, James A.; Botha,
Gert J. J.; Régnier, Stéphane
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.
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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.
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.
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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.
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.
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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
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.
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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.
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.
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Title: Damping of Propagating Kink Waves in the Solar Corona
Authors: Tiwari, Ajay K.; Morton, Richard J.; Régnier, Stéphane;
McLaughlin, James A.
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.
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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.
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<SUP>-1</SUP>, 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 v<SUB>x</SUB> and v<SUB>y</SUB> 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 10<SUP>4</SUP> K with the distribution of
v<SUB>x</SUB>, 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.
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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.
2019SoPh..294...38B Altcode:
Correction to: Solar Phys (2018)
293:75https://doi.org/10.1007/s11207-018-1278-5 <P />Please find in
this correction document the correct versions of abstract, Sect. 3.1
and Figs. 3 and 12.
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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.
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<SUP>−1</SUP> 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<SUP>−1</SUP> 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.
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<SUP>-1</SUP>,
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.
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.
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.
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.
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.
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
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
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.
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.
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. <BR /> Aims: We aim to contribute to the
overall understanding of MHD wave propagation within inhomogeneous
media, specifically around X-lines. <BR /> 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. <BR /> 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. <BR />
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.
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.
2015A&A...581A...9R Altcode: 2015arXiv150707350R
<BR /> Aims: The electron plasma frequency ω<SUB>pe</SUB> and
electron gyrofrequency Ω<SUB>e</SUB> 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. <BR /> Methods: We perform an in-depth
analysis of the ω<SUB>pe</SUB>/Ω<SUB>e</SUB> 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 ω<SUB>pe</SUB>/Ω<SUB>e</SUB>
is affected by the potential and non-linear force-free field
models. <BR /> 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
ω<SUB>pe</SUB>/Ω<SUB>e</SUB>≤ 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 ω<SUB>pe</SUB>/Ω<SUB>e</SUB> are lower for non-linear force-free
fields than potential fields, thus increasing the possibility of maser
instability in the corona. <BR /> Conclusions: From this new approach
for estimating ω<SUB>pe</SUB>/Ω<SUB>e</SUB>, 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.
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. <BR /> Aims: In this paper, a new method of estimating
the size and temperature profile of the chromospheric cavity above a
sunspot umbra is developed. <BR /> 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. <BR />
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. <BR /> 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.
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.
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.
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 10<SUP>26</SUP> erg.
---------------------------------------------------------
Title: Magnetic Field Extrapolations into the Corona: Success and
Future Improvements
Authors: Régnier, S.
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.
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
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<SUP>-1</SUP>) 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.
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
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
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.
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.
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.
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. <BR /> 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. <BR /> 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). <BR /> 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. <BR /> 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. <P />Appendix A and two movies are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Flows at the Edge of an Active Region: Observation and
Interpretation
Authors: Boutry, C.; Buchlin, E.; Vial, J. -C.; Régnier, S.
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.
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.
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<SUP>−1</SUP>),
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.
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.
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.
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.
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. <BR /> Aims: We aim at defining
the structure of a polar crown cavity and describing its evolution
during the erupting process. <BR /> 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. <BR /> 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). <BR /> 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<SUP>-1</SUP> and an acceleration phase at a mean
speed of 25 km s<SUP>-1</SUP>. <P />Two movies are only available at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
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.
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.
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.
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.
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.
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.
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
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.
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 10<SUP>42</SUP> Mx<SUP>2</SUP>
(10<SUP>26</SUP> Wb<SUP>2</SUP>), 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. <BR />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. <BR />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. <BR />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.
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.
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.
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). <BR
/>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. <BR />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<SUP>-1</SUP>). 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<SUP>-1</SUP> and depart
highly from potential field values. <BR />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.
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.
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. <BR />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. <BR />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. <BR />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. <BR />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.
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.
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 ~10<SUP>32</SUP> 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
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
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
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.
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.
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. <BR />Aims: The object is to
understand the diverse and complex nature of coronal magnetic fields
in active regions using a nonlinear force-free model. <BR />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. <BR />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.
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
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
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.
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
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 E<SUB>n</SUB> = « |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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 J<SUB>z</SUB> 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.
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.
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. <P />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. <P />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. <P
/>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.
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.
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.
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.
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.
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.
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.
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. <P />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.
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.
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.
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.
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 180<SUP>deg</SUP>),
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*E<SUP>31</SUP> erg and the relative magnetic helicity to
4.7*E<SUP>34</SUP> G<SUP>2</SUP> cm<SUP>4</SUP>. 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.
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.
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 18<SUP>deg</SUP>,
and the magnetic field strength B (G) is proportional to the square
root of the density rho<SUB>o</SUB> (cm<SUP>-3</SUP>) in the slab,
B ~ 2.9 x 10<SUP>-5</SUP> sqrt {rho<SUB>o</SUB>}.
---------------------------------------------------------
Title: Reconstruction of the Coronal Magnetic Field for Active Region
NOAA 8151
Authors: Régnier, S.; Amari, T.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1984LPICo.537E..53R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measurement of cross sections for <SUP>22</SUP>Na,
<SUP>20-22</SUP>Ne and <SUP>36-42</SUP>Ar in the spallation of Mg,
Al, Si, Ca and Fe. Production ratios of some cosmogenic nuclidesin
meteorites.
Authors: Baros, F.; Regnier, S.
1984JPhys..45..855B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: <SUP>22</SUP>Na/<SUP>22</SUP>Ne and
<SUP>26</SUP>Al/<SUP>21</SUP>Ne Production Ratios in Iron Meteorites
Authors: Regnier, S.; Baros, F.; Lavielle, B.; Simonoff, G. N.
1983Metic..18Q.384R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: About Cosmogenic Krypton in Iron Meteorites
Authors: Lavielle, B.; Regnier, S.
1983Metic..18R.335L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: More About Cosmogenic Krypton
Authors: Regnier, S.; Lavielle, B.; Simonoff, G. N.
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.
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.
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 <SUP>78-86</SUP>Kr,
<SUP>74</SUP>As, <SUP>75</SUP>Se, <SUP>83,84,86</SUP>Rb,
<SUP>85</SUP>Sr, <SUP>88</SUP>Y, <SUP>88,95</SUP>Zr, and
<SUP>92</SUP>Nb<SUP>m</SUP> were measured using high-sensitivity mass
spectrometry and nondestructive γ counting. Lighter products such as
<SUP>38,39,42</SUP>Ar and 12 radioactive isotopes from <SUP>7</SUP>Be
to <SUP>65</SUP>Zn 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, <SUP>83</SUP>Kr is predicted with a precision better than
33% (1σ) and the production ratios <SUP>i</SUP>Kr/<SUP>83</SUP>Kr are
predicted to better than 25%. It is concluded that the cosmogenic ratios
<SUP>86</SUP>Kr/<SUP>83</SUP>Kr and <SUP>81</SUP>Kr/<SUP>83</SUP>Kr
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
<SUP>89</SUP>Y and Zr, (p, spallation) E=0.059-24 GeV; measured σ(E)
for <SUP>78-86</SUP>Kr 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.
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.
1980E&PSL..50..156N Altcode:
A systematic calibration of the production rate of one specific
cosmic-ray-produced nuclide in chondrites, that of <SUP>21</SUP>Ne,
was achieved by using four independent methods: P <SUB>21</SUB>(1.11)
= 0.507 ± 0.039, 0.302 ± 0.013, 0.312 ± 0.017and0.292 ± 0.019
(in units of 10 <SUP>-8</SUP> cm <SUP>3</SUP> STP/g My) based
on <SUP>26</SUP>Al-age, <SUP>53</SUP>Mn-age, <SUP>81</SUP>Kr-
<SUP>83</SUP>Kr and <SUP>22</SUP>Na- <SUP>22</SUP>Ne methods,
respectively. These production rates are all normalized to a shielding
parameter ratio <SUP>22</SUP>Ne/ <SUP>21</SUP>Ne= 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 <SUP>26</SUP>Al-age calibration. Based on these results,
we recommend a value P <SUB>21</SUB>(1.11) = 0.31 and a production
rate equation:P <SUB>21</SUB> = 4.845 P <SUB>21</SUB> (1.11) F[21.77(
<SUP>22</SUP>Ne/ <SUP>21</SUP>Ne) - 19.32] <SUP>-</SUP>, 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 <SUP>26</SUP>Al 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.
1979Metic..14..499N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pu-Nd-Xe Dating: A Stepwise Approach
Authors: Marti, K.; Kurtz, J. P.; Regnier, S.
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.
1979PhRvC..20.1517R Altcode:
Spallation ratios and production cross sections of
<SUP>36,38,39,42</SUP>Ar 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)<SUB>T</SUB> ratios of the target and there is
probably a linear correlation between the position of the peak of the
spallation distribution and the (NZ)<SUB>T</SUB> 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 <SUP>36, 38, 39, 42</SUP>Ar; 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.
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.
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.
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.
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.
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.
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: Cl<SUP>36</SUP> and the age of the cosmic rays.
Authors: Cassé, M.; Goret, P.; Regnier, S.
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.
1975CRASB.280..513R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Production de <SUP>26</SUP>Al dans Fe et St par protons de
0.6 et 24 GeV
Authors: Regnier, S.; Lagarde, M.; Simonoff, G. N.; Yokoyama, Y.
1973E&PSL..18....9R Altcode:
Cross sections for <SUP>26</SUP>Al 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) <SUP>26</SUP>Al,
of great astrophysical interest, by analogy with known equivalent
nuclear reactions.
