45 research outputs found
Coronal mass ejection-related particle acceleration regions during a simple eruptive event
International audienceAn intriguing feature of many solar energetic particle (SEP) events is the detection of particles over a very extended range of longitudes in the heliosphere. This may be due to peculiarities of the magnetic field in the corona, to a broad accelerator, to cross-field transport of the particles, or to a combination of these processes. The eruptive flare on 26 April 2008 provided an opportunity to study relevant processes under particularly favourable conditions since it occurred in a very quiet solar and interplanetary environment. This enabled us to investigate the physical link between a single well-identified coronal mass ejection (CME), electron acceleration as traced by radio emission, and the production of SEPs. We conduct a detailed analysis, which combines radio observations (Nançay Radio Heliograph and Nançay Decametre Array, Wind/Waves spectrograph) with remote-sensing observations of the corona in extreme ultraviolet (EUV) and white light, as well as in situ measurements of energetic particles near 1AU (SoHO and STEREO spacecraft). By combining images taken from multiple vantage points, we were able to derive the time-dependent evolution of the 3D pressure front that was developing around the erupting CME. Magnetic reconnection in the post-CME current sheet accelerated electrons, which remained confined in closed magnetic fields in the corona, while the acceleration of escaping particles can be attributed to the pressure front ahead of the expanding CME. The CME accelerated electrons remotely from the parent active region, owing to the interaction of its laterally expanding flank, which was traced by an EUV wave, with the ambient corona. SEPs detected at one STEREO spacecraft and SoHO were accelerated later, when the frontal shock of the CME intercepted the spacecraft-connected interplanetary magnetic field line. The injection regions into the heliosphere inferred from the radio and SEP observations are separated in longitude by about 140 •. The observations for this event show that it is misleading to interpret multi-spacecraft SEP measurements in terms of one acceleration region in the corona. The different acceleration regions are linked to different vantage points in the interplanetary space
Production of sunspots and their effects on the corona and solar wind: Insights from a new 3D flux-transport dynamo model
We present a three-dimensional numerical model for the generation and
evolution of the magnetic field in the solar convection zone, in which sunspots
are produced and contribute to the cyclic reversal of the large-scale magnetic
field. We then assess the impact of this dynamo-generated field on the
structure of the solar corona and solar wind. This model solves the induction
equation in which the velocity field is prescribed. This velocity field is a
combination of a solar-like differential rotation and meridional circulation.
We develop an algorithm that enables the magnetic flux produced in the interior
to be buoyantly transported towards the surface to produce bipolar spots. We
find that those tilted bipolar magnetic regions contain a sufficient amount of
flux to periodically reverse the polar magnetic field and sustain dynamo
action. We then track the evolution of these magnetic features at the surface
during a few consecutive magnetic cycles and analyze their effects on the
topology of the corona and on properties of the solar wind (distribution of
streamers and coronal holes, and of slow and fast wind streams) in connection
with current observations of the Sun.Comment: 18 pages, 10 figure
Parametric study of the kinematic evolution of coronal mass ejection shock waves and their relation to flaring activity
Coronal and interplanetary shock waves produced by coronal mass ejections
(CMEs) are major drivers of space-weather phenomena, inducing major changes in
the heliospheric radiation environment and directly perturbing the near-Earth
environment, including its magnetosphere. A better understanding of how these
shock waves evolve from the corona to the interplanetary medium can therefore
contribute to improving nowcasting and forecasting of space weather. Early
warnings from these shock waves can come from radio measurements as well as
coronagraphic observations that can be exploited to characterise the dynamical
evolution of these structures. Our aim is to analyse the geometrical and
kinematic properties of 32 CME shock waves derived from multi-point white-light
and ultraviolet imagery taken by the Solar Dynamics Observatory (SDO), Solar
and Heliospheric Observatory (SoHO), and Solar-Terrestrial Relations
Observatory (STEREO) to improve our understanding of how shock waves evolve in
3D during the eruption of a CME. We use our catalogue to search for relations
between the shock wave's kinematic properties and the flaring activity
associated with the underlying genesis of the CME piston. Past studies have
shown that shock waves observed from multiple vantage points can be aptly
reproduced geometrically by simple ellipsoids. The catalogue of reconstructed
shock waves provides the time-dependent evolution of these ellipsoidal
parameters. From these parameters, we deduced the lateral and radial expansion
speeds of the shocks evolving over time. We compared these kinematic properties
with those obtained from a single viewpoint by SoHO in order to evaluate
projection effects. Finally, we examined the relationships between the shock
wave and the associated flare when the latter was observed on the disc by
considering the measurements of soft and hard X-rays.Comment: 11 pages, 12 figures, accepted for publication in A&
On the variability of the slow solar wind: New insights from the modelling and PSP-WISPR observations
We analyse the signature and origin of transient structures embedded in the
slow solar wind, and observed by the Wide-Field Imager for Parker Solar Probe
(WISPR) during its first 10 passages close to the Sun. WISPR provides a new
in-depth vision on these structures, which have long been speculated to be a
remnant of the pinch-off magnetic reconnection occurring at the tip of helmet
streamers. We pursue the previous modelling works of Reville (2020b, 2022) that
simulate the dynamic release of quasi-periodic density structures into the slow
wind through a tearing-induced magnetic reconnection at the tip of helmet
streamers. Synthetic WISPR white-light (WL) images are produced using a newly
developed advanced forward modelling algorithm, that includes an adaptive grid
refinement to resolve the smallest transient structures in the simulations. We
analyse the aspect and properties of the simulated WL signatures in several
case studies, typical of solar minimum and near-maximum configurations.
Quasi-periodic density structures associated with small-scale magnetic flux
ropes are formed by tearing-induced magnetic reconnection at the heliospheric
current sheet and within 3-7Rs. Their appearance in WL images is greatly
affected by the shape of the streamer belt and the presence of
pseudo-streamers. The simulations show periodicities on the ~90-180min, ~7-10hr
and ~25-50hr timescales, which are compatible with WISPR and past observations.
This work shows strong evidence for a tearing-induced magnetic reconnection
contributing to the long-observed high variability of the slow solar wind.Comment: 23 pages, 14 figures, to appear in Astronomy & Astrophysics,
associated movies available at https://doi.org/10.5281/zenodo.813559
Investigating the Origin of the First Ionization Potential Effect With a Shell Turbulence Model
International audienceThe enrichment of coronal loops and the slow solar wind with elements that have low First Ionization Potential, known as the FIP effect, has often been interpreted as the tracer of a common origin. A current explanation for this FIP fractionation rests on the influence of ponderomotive forces and turbulent mixing acting at the top of the chromosphere. The implied wave transport and turbulence mechanisms are also key to wave-driven coronal heating and solar wind acceleration models. This work makes use of a shell turbulence model run on open and closed magnetic field lines of the solar corona to investigate with a unified approach the influence of magnetic topology, turbulence amplitude and dissipation on the FIP fractionation. We try in particular to assess whether there is a clear distinction between the FIP effect on closed and open field regions
The Solar Origin of Particle Events Measured by Parker Solar Probe
During the second solar encounter phase of Parker Solar Probe (PSP), two small solar energetic particle (SEP) events were observed by the Integrated Science Investigation of the Sun, on 2019 April 2 and 4. At the time, PSP was approaching its second perihelion at a distance of ~24.8 million kilometers from the solar center, it was in near-radial alignment with STEREO-A and in quadrature with Earth. During the two SEP events multiple narrow ejections and a streamer-blowout coronal mass ejection (SBO-CME) originated from a solar region situated eastward of PSP. We analyze remote-sensing observations of the solar corona, and model the different eruptions and how PSP was connected magnetically to the solar atmosphere to determine the possible origin of the two SEP events. We find that the SEP event on April 2 was associated with the two homologous ejections from active region 12738 that included two surges and EUV waves occurring in quick succession. The EUV waves appear to merge and were fast enough to form a shock in the low corona. We show that the April 4 SEP event originates in the SBO-CME. Our modeling work suggests that formation of a weak shock is likely for this CME
HelioCast: heliospheric forecasting based on white-light observations of the solar corona. I. Solar minimum conditions
We present a new 3D MHD heliospheric model for space-weather forecasting
driven by boundary conditions defined from white-light observations of the
solar corona. The model is based on the MHD code PLUTO, constrained by an
empirical derivation of the solar wind background properties at 0.1au. This
empirical method uses white-light observations to estimate the position of the
heliospheric current sheet. The boundary conditions necessary to run HelioCast
are then defined from pre-defined relations between the necessary MHD
properties (speed, density and temperature) and the distance to the current
sheet. We assess the accuracy of the model over six Carrington rotations during
the first semester of 2018. Using point-by-point metrics and event based
analysis, we evaluate the performances of our model varying the angular width
of the slow solar wind layer surrounding the heliospheric current sheet. We
also compare our empirical technique with two well tested models of the corona:
Multi-VP and WindPredict-AW. We find that our method is well suited to
reproduce high speed streams, and does -- for well chosen parameters -- better
than full MHD models. The model shows, nonetheless, limitations that could
worsen for rising and maximum solar activity.Comment: Accepted for publication in the Journal of Space Weather and Space
Climate. 23 pages, 12 figures. The model runs live at
http://heliocast.irap.omp.eu
The Solar Origin of Particle Events Measured by Parker Solar Probe
During the second solar encounter phase of Parker Solar Probe (PSP), two small solar energetic particle (SEP) events were observed by the Integrated Science Investigation of the Sun, on 2019 April 2 and 4. At the time, PSP was approaching its second perihelion at a distance of ~24.8 million kilometers from the solar center, it was in near-radial alignment with STEREO-A and in quadrature with Earth. During the two SEP events multiple narrow ejections and a streamer-blowout coronal mass ejection (SBO-CME) originated from a solar region situated eastward of PSP. We analyze remote-sensing observations of the solar corona, and model the different eruptions and how PSP was connected magnetically to the solar atmosphere to determine the possible origin of the two SEP events. We find that the SEP event on April 2 was associated with the two homologous ejections from active region 12738 that included two surges and EUV waves occurring in quick succession. The EUV waves appear to merge and were fast enough to form a shock in the low corona. We show that the April 4 SEP event originates in the SBO-CME. Our modeling work suggests that formation of a weak shock is likely for this CME