254 research outputs found
Current driven weak double layers
Double layers in plasmas can be created by different means. For example, a potential difference forms between two plasmas with different temperatures, in a plasma jet flowing along a converging magnetic field, in a quiescent plasma submitted to an external difference of potential, or in a turbulent plasma carrying an electric charge. The first three cases can be current-free, but not necessarily, although the numerical simulations were made under such conditions for the first two points. Apart from the third case, which is mainly of interest for laboratory experiments, these double layers are good candidates for accelerating the auroral electrons to the few kiloelectron volts observed
Solar wind charge exchange X-ray emission from Mars Model and data comparison
Aims. We study the soft X-ray emission induced by charge exchange (CX)
collisions between solar-wind, highly charged ions and neutral atoms of the
Martian exosphere. Methods. A 3D multi species hybrid simulation model with
improved spatial resolution (130 km) is used to describe the interaction
between the solar wind and the Martian neutrals. We calculated velocity and
density distributions of the solar wind plasma in the Martian environment with
realistic planetary ions description, using spherically symmetric exospheric H
and O profiles. Following that, a 3D test-particle model was developed to
compute the X-ray emission produced by CX collisions between neutrals and solar
wind minor ions. The model results are compared to XMM-Newton observations of
Mars. Results. We calculate projected X-ray emission maps for the XMM-Newton
observing conditions and demonstrate how the X-ray emission reflects the
Martian electromagnetic structure in accordance with the observed X-ray images.
Our maps confirm that X-ray images are a powerful tool for the study of solar
wind - planetary interfaces. However, the simulation results reveal several
quantitative discrepancies compared to the observations. Typical solar wind and
neutral coronae conditions corresponding to the 2003 observation period of Mars
cannot reproduce the high luminosity or the corresponding very extended halo
observed with XMM-Newton. Potential explanations of these discrepancies are
discussed.Comment: 10 pages, 5 figures, accepted for publication in Astron. Astrophysic
Dynamic Martian magnetosphere: Transient twist induced by a rotation of the IMF
International audienceSimulation studies of the Martian environment are usually restricted to stationary situations under various steady conditions of the solar wind and solar radiation. Dynamic transients and their implications have so far attracted little attention although global simulation models can provide valuable insights to understand disagreements between simulations and in situ observations. We make use of a three dimensional multispecies hybrid simulation model to investigate the response of the Martian plasma environment to a sudden rotation of the IMF. The simulation model couples charged and neutral species via three ionisation mechanisms: the absorption of solar extreme ultraviolet radiation, the impact of solar wind electrons, and the charge exchange between ions and neutral atoms. When a rotational discontinuity conveyed by the solar wind reaches the Martian environment the bow shock adapts quickly to the new solar wind conditions in contrast to the induced magnetosphere, especially the magnetic lobes in the wake. Timescales necessary to recover a stationary state can be estimated from such simulations and have some implications for space observations especially in the use of magnetic field proxies and for organizing particle measurements made by a spacecraft like Mars Express without an onboard magnetometer
Composition Structure of Interplanetary Coronal Mass Ejections From Multispacecraft Observations, Modeling, and Comparison with Numerical Simulations
We present an analysis of the ionic composition of iron for two
interplanetary coronal mass ejections observed in May 21-23 2007 by the ACE and
STEREO spacecraft in the context of the magnetic structure of the ejecta flux
rope, sheath region, and surrounding solar wind flow. This analysis is made
possible due to recent advances in multispacecraft data interpolation,
reconstruction, and visualization as well as results from recent modeling of
ionic charge states in MHD simulations of magnetic breakout and flux
cancellation CME initiation. We use these advances to interpret specific
features of the ICME plasma composition resulting from the magnetic topology
and evolution of the CME. We find that in both the data and our MHD
simulations, the flux ropes centers are relatively cool, while charge state
enhancements surround and trail the flux ropes. The magnetic orientation of the
ICMEs are suggestive of magnetic breakout-like reconnection during the eruption
process, which could explain the spatial location of the observed iron
enhancements just outside the traditional flux rope magnetic signatures and
between the two ICMEs. Detailed comparisons between the simulations and data
were more complicated, but a sharp increase in high iron charge states in the
ACE and STEREO-A data during the second flux rope corresponds well to similar
features in the flux cancellation results. We discuss the prospects of this
integrated in-situ data analysis and modeling approach to advancing our
understanding of the unified CME-to-ICME evolution.Comment: Accepted for submission to The Astrophysical Journa
A global hybrid model for Mercury's interaction with the solar wind: Case study of the dipole representation
International audienceThe interaction of the solar wind (SW) with the magnetic field of Mercury is investigated by means of a three dimensional parallelized multispecies hybrid model. A comparison between two mathematical representations of Mercury's intrinsic magnetic field is studied. The first model is an Offset Dipole (OD) having the offset and dipolar moment reported by Anderson et al. (2011). The second model is a combination of a Dipole and a Quadrupole (DQ), the total field is fitted to the offset dipolar field, for northern latitudes greater than 50°. Simulations reproduce the features which characterize Mercury's interaction with the SW, encompassing the Bow Shock (BS), the magnetosheath, the magnetotail, the "cusps" region and the neutral current sheet. Global hybrid simulations of the Hermean magnetosphere run for the OD and DQ models demonstrate that the southern parts of the magnetospheres produced by the OD and DQ models differ greatly in topology and volume meanwhile their northern parts-are quite similar. In particular the DQ model exhibits a dome of closed field lines around the south pole in contrast to the OD. Without further information on the intrinsic magnetic field of the planet in the southern region which should be provided by BepiColombo after year 2020, we can only speculate on the influence of the different magnetic topologies on the magnetospheric dynamics
Influence of the solar EUV flux on the Martian plasma environment
The interaction of the solar wind with the Martian atmosphere and ionosphere is investigated by using three-dimensional, global and multi-species hybrid simulations. In the present work we focus on the influence of the solar EUV flux on the Martian plasma environment by comparing simulations done for conditions representative of the extrema of the solar cycle. The dynamics of four ionic species (H<sup>+</sup>, He<sup>++</sup>, O<sup>+</sup>, O<sub>2</sub><sup>+</sup>), originating either from the solar wind or from the planetary plasma, is treated fully kinetically in the simulation model in order to characterize the distribution of each component of the plasma, both at solar maximum and at solar minimum. The solar EUV flux controls the ionization frequencies of the exospheric species, atomic hydrogen and oxygen, as well as the density, the temperature, and thus the extension of the exosphere. Ionization by photons and by electron impacts, and the main charge exchange reactions are self-consistently included in the simulation model. Simulation results are in reasonable agreement with the observations made by Phobos-2 and Mars Global Surveyor (MGS) spacecraft: 1) the interaction creates a cavity, void of solar wind ions (H<sup>+</sup>, He<sup>++</sup>), which depends weakly upon the phase of the solar cycle, 2) the motional electric field of the solar wind flow creates strong asymmetries in the Martian environment, 3) the spatial distribution of the different components of the planetary plasma depends strongly upon the phase of the solar cycle. The fluxes of the escaping planetary ions are computed from the simulated data and results for solar maximum are compared with estimates based on the measurements made by experiments ASPERA and TAUS on board Phobos-2
Advancing In Situ Modeling of ICMEs: New Techniques for New Observations
It is generally known that multi-spacecraft observations of interplanetary
coronal mass ejections (ICMEs) more clearly reveal their three-dimensional
structure than do observations made by a single spacecraft. The launch of the
STEREO twin observatories in October 2006 has greatly increased the number of
multipoint studies of ICMEs in the literature, but this field is still in its
infancy. To date, most studies continue to use on flux rope models that rely on
single track observations through a vast, multi-faceted structure, which
oversimplifies the problem and often hinders interpretation of the large-scale
geometry, especially for cases in which one spacecraft observes a flux rope,
while another does not. In order to tackle these complex problems, new modeling
techniques are required. We describe these new techniques and analyze two ICMEs
observed at the twin STEREO spacecraft on 22-23 May 2007, when the spacecraft
were separated by ~8 degrees. We find a combination of non-force-free flux rope
multi-spacecraft modeling, together with a new non-flux rope ICME plasma flow
deflection model, better constrains the large-scale structure of these ICMEs.
We also introduce a new spatial mapping technique that allows us to put
multispacecraft observations and the new ICME model results in context with the
convecting solar wind. What is distinctly different about this analysis is that
it reveals aspects of ICME geometry and dynamics in a far more visually
intuitive way than previously accomplished. In the case of the 22-23 May ICMEs,
the analysis facilitates a more physical understanding of ICME large-scale
structure, the location and geometry of flux rope sub-structures within these
ICMEs, and their dynamic interaction with the ambient solar wind
Planetary Science Virtual Observatory architecture
In the framework of the Europlanet-RI program, a prototype of Virtual
Observatory dedicated to Planetary Science was defined. Most of the activity
was dedicated to the elaboration of standards to retrieve and visualize data in
this field, and to provide light procedures to teams who wish to contribute
with on-line data services. The architecture of this VO system and selected
solutions are presented here, together with existing demonstrators
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