300 research outputs found
The August 24, 2002 Coronal Mass Ejection: When a Western Limb Event Connects to Earth
We discuss how some coronal mass ejections (CMEs) originating from the
western limb of the Sun are associated with space weather effects such as solar
energetic particles (SEPs), shock or geo-effective ejecta at Earth. We focus on
the August 24, 2002 coronal mass ejection, a fast (~ 2000 km/s) eruption
originating from W81. Using a three-dimensional magneto-hydrodynamic simulation
of this ejection with the Space Weather Modeling Framework (SWMF), we show how
a realistic initiation mechanism enables us to study the deflection of the CME
in the corona and the heliosphere. Reconnection of the erupting magnetic field
with that of neighboring streamers and active regions modify the solar
connectivity of the field lines connecting to Earth and can also partly explain
the deflection of the eruption during the first tens of minutes. Comparing the
results at 1 AU of our simulation with observations by the ACE spacecraft, we
find that the simulated shock does not reach Earth, but has a maximum angular
span of about 120, and reaches 35 West of Earth in 58 hours. We
find no significant deflection of the CME and its associated shock wave in the
heliosphere, and we discuss the consequences for the shock angular span.Comment: 7 pages, 4 figures, IAU 257 Symposium Proceeding
L\'evy Ratchet in a Weak Noise Limit: Theory and Simulation
We study the motion of a particle embedded in a time independent periodic
potential with broken mirror symmetry and subjected to a L\'evy noise
possessing L\'evy stable probability law (L\'evy ratchet). We develop
analytical approach to the problem based on the asymptotic probabilistic method
of decomposition proposed by P. Imkeller and I. Pavlyukevich [J. Phys. A
{\bf39}, L237 (2006); Stoch. Proc. Appl. {\bf116}, 611 (2006)]. We derive
analytical expressions for the quantities characterizing the particle motion,
namely the splitting probabilities of first escape from a single well, the
transition probabilities and the particle current. A particular attention is
devoted to the interplay between the asymmetry of the ratchet potential and the
asymmetry (skewness) of the L\'evy noise. Intensive numerical simulations
demonstrate a good agreement with the analytical predictions for sufficiently
small intensities of the L\'evy noise driving the particle.Comment: 14 pages, 11 figures, 63 reference
A Titov-D\'emoulin Type Eruptive Event Generator for Plasmas
We provide exact analytical solutions for the magnetic field produced by
prescribed current distributions located inside a toroidal filament of finite
thickness. The solutions are expressed in terms of toroidal functions which are
modifications of the Legendre functions. In application to the MHD equilibrium
of a twisted toroidal current loop in the solar corona, the Grad-Shafranov
equation is decomposed into an analytic solution describing an equilibrium
configuration against the pinch-effect from its own current and an approximate
solution for an external strapping field to balance the hoop force. Our
solutions can be employed in numerical simulations of coronal mass ejections.
When superimposed on the background solar coronal magnetic field, the excess
magnetic energy of the twisted current loop configuration can be made unstable
by applying flux cancellation to reduce the strapping field. Such loss of
stability accompanied by the formation of an expanding flux rope is typical for
the Titov & D\'emoulin (1999) eruptive event generator. The main new features
of the proposed model are: (i) The filament is filled with finite
plasma with finite mass and energy, (ii) The model describes an equilibrium
solution that will spontaneously erupt due to magnetic reconnection of the
strapping magnetic field arcade, and (iii) There are analytic expressions
connecting the model parameters to the asymptotic velocity and total mass of
the resulting CME, providing a way to connect the simulated CME properties to
multipoint coronograph observations.Comment: 20 pages, 7 figure
Eruptive Event Generator Based on the Gibson-Low Magnetic Configuration
Coronal Mass Ejections (CMEs), a kind of energetic solar eruptions, are an
integral subject of space weather research. Numerical magnetohydrodynamic (MHD)
modeling, which requires powerful computational resources, is one of the
primary means of studying the phenomenon. With increasing accessibility of such
resources, grows the demand for user-friendly tools that would facilitate the
process of simulating CMEs for scientific and operational purposes. The
Eruptive Event Generator based on Gibson-Low flux rope (EEGGL), a new publicly
available computational model presented in this paper, is an effort to meet
this demand. EEGGL allows one to compute the parameters of a model flux rope
driving a CME via an intuitive graphical user interface (GUI). We provide a
brief overview of the physical principles behind EEGGL and its functionality.
Ways towards future improvements of the tool are outlined
Exoplanet Radio Transits as a Probe for Exoplanetary Magnetic Fields -- Time-dependent MHD Simulations
We perform a series of time dependent Magnetohydrodynamic simulations of the
HD 189733 star-planet system in order to predict radio transit modulations due
to the interaction between the stellar wind and planetary magnetic field. The
simulation combines a model for the stellar corona and wind with an exoplanet
that is orbiting the star in a fully dynamic, time-dependent manner. Our
simulations generate synthetic radio images that enable us to obtain synthetic
radio lightcurves in different frequencies. We find a clear evidence for the
planetary motion in the radio light curves. Moreover, we find specific repeated
features in the light curves that are attributed to the passage of the
planetary magnetosphere in front of the star during transit. More importantly,
we find a clear dependence in the magnitude and phase of these lightcurve
features on the strength of the planetary magnetic field. Our work demonstrates
that if radio transits could be observed, they could indeed provide information
about the magnetic field strength of the transiting exoplanet. Future work to
parameterize these lightcurve features and their dependence on the planetary
field strength would provide tools to search for these features in radio
observations datasets. As we only consider the thermal radio emission from the
host star for our study, very sensitive radio interferometers are necessary to
detect these kinds of planetary transit in radio.Comment: 19 Pages, 10 Figure
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