130 research outputs found
Formation, Propagation, and Decay of Coherent Pulses of Solar Cosmic Rays
We have performed numerical simulations of the interplanetary transport of
solar cosmic rays. The particles form a coherent pulse within AU
after their injection. The gradual decrease of a pulse's speed and anisotropy
can be understood in terms of an equilibrium between pitch-angle scattering and
focusing. The results should be useful for estimating times of particle
injection.Comment: 4 pages (LaTeX) + 4 uuencoded-tarred-compressed postscript figures,
uses agupp.sty (available from ftp://xxx.lanl.gov/macros or
ftp://kosmos.agu.org/agutex), one 3D surface plot FAXed upon request.
Accepted by Geophysical Research Letter
Flare magnetic reconnection and relativistic particles in the 2003 October 28 event
An X17.2 solar flare occurred on 2003 October 28, accompanied by
multi-wavelength emissions and a high flux of relativistic particles observed
at 1AU. We present the analytic results of the TRACE, SOHO, RHESSI, ACE, GOES,
hard X-ray (INTEGRAL satellite), radio (Onderejov radio telescope), and neutron
monitor data. It is found that the inferred magnetic reconnection electric
field correlates well with the hard X-ray, gamma-ray, and neutron emission at
the Sun. Thus the flare's magnetic reconnection probably makes a crucial
contribution to the prompt relativistic particles, which could be detected at 1
AU. Since the neutrons were emitted a few minutes before the injection of
protons and electrons, we propose a magnetic-field evolution configuration to
explain this delay. We do not exclude the effect of CME-driven shock, which
probably plays an important role in the delayed gradual phase of solar
energetic particles.Comment: 5 pages, 7 figures, accepted by A&
The acceleration characteristics of solar energetic particles in the 2000 July 14 event
In large gradual solar energetic particle (SEP) events, especially the
ground-level enhancement (GLE) events, where and how energetic particles are
accelerated is still a problem. By using imaging data from TRACE, Yohkoh/HXT,
SOHO/MDI and SOHO/EIT, along with the data from the GOES, Apatity NM, and
SOHO/LASCO CME catalog, the evolution of the X5.7 two-ribbon flare and the
associated SEP event on 14 July 2000 are studied. It is found that the magnetic
reconnection in this event consists of two parts, and the induced electric
field Erec is temporally correlated with the evolution of hard X-ray and
gamma-ray emission. In particular, the first hard X-ray and gamma-ray emission
peak occurred at 10:22 UT, corresponding to the magnetic reconnection in the
western part of the flare ribbons and the maximum Erec of 9.5 V/cm; the second
emission peak at 10:27 UT, corresponding to the eastern part and the maximum
Erec of 13.0 V/cm. We also analyze the SEP injection profiles as functions of
time and CME-height, and find two-component injection which may result from
different acceleration mechanisms. A reasonable conclusion is that reconnection
electric field makes a crucial contribution to the acceleration of relativistic
particles and to the impulsive component of the large gradual SEP event, while
CME-driven shocks play a dominant role in the gradual component.Comment: 6 pages, 7 figures, A&A, 461, 111
Modeling impacts of geomagnetic field variations on middle atmospheric ozone responses to solar proton events on long timescales
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94922/1/jgrd13876.pd
Estimations of changes of the Sun's mass and the gravitation constant from the modern observations of planets and spacecraft
More than 635 000 positional observations (mostly radiotechnical) of planets
and spacecraft (1961-2010), have been used for estimating possible changes of
the gravitation constant, the solar mass, and semi-major axes of planets, as
well as the value of the astronomical unit, related to them. The analysis of
the observations has been performed on the basis of the EPM2010 ephemerides of
IAA RAS in post-newtonian approximation. The obtained results indicate on
decrease in the heliocentric gravitation constant per year at the level The positive secular
changes of semi-major axes have been obtained simultaneously
for the planets Mercury, Venus, Mars, Jupiter, Saturn, as expected if the
geliocentric gravitation constant is decreasing in century wise. The change of
the mass of the Sun due to the solar radiation and the solar wind and
the matter dropping on the Sun (comets, meteors, asteroids and dust) was
estimated. Taking into account the maximal limits of the possible
change, the value falls within the interval in year with the 95% probability. The
astronomical unit (au) is only connected with the geliocentric gravitation
constant by its definition. In the future, the connection between
and au should be fixed at the certain time moment, as it is inconvenient highly
to have the changing value of the astronomical unit.Comment: 20 pages, 4 tables, accepted for publication in Solar System
Research, 2011 (Astronomicheskii vestnik
On the protection of extrasolar Earth-like planets around K/M stars against galactic cosmic rays
Previous studies have shown that extrasolar Earth-like planets in close-in
habitable zones around M-stars are weakly protected against galactic cosmic
rays (GCRs), leading to a strongly increased particle flux to the top of the
planetary atmosphere. Two main effects were held responsible for the weak
shielding of such an exoplanet: (a) For a close-in planet, the planetary
magnetic moment is strongly reduced by tidal locking. Therefore, such a
close-in extrasolar planet is not protected by an extended magnetosphere. (b)
The small orbital distance of the planet exposes it to a much denser stellar
wind than that prevailing at larger orbital distances. This dense stellar wind
leads to additional compression of the magnetosphere, which can further reduce
the shielding efficiency against GCRs. In this work, we analyse and compare the
effect of (a) and (b), showing that the stellar wind variation with orbital
distance has little influence on the cosmic ray shielding. Instead, the weak
shielding of M star planets can be attributed to their small magnetic moment.
We further analyse how the planetary mass and composition influence the
planetary magnetic moment, and thus modify the cosmic ray shielding efficiency.
We show that more massive planets are not necessarily better protected against
galactic cosmic rays, but that the planetary bulk composition can play an
important role.Comment: 7 figure
Forbush decreases and solar events seen in the 10 - 20GeV energy range by the Karlsruhe Muon Telescope
Since 1993, a muon telescope located at Forschungszentrum Karlsruhe
(Karlsruhe Muon Telescope) has been recording the flux of single muons mostly
originating from primary cosmic-ray protons with dominant energies in the 10 -
20 GeV range. The data are used to investigate the influence of solar effects
on the flux of cosmic-rays measured at Earth. Non-periodic events like Forbush
decreases and ground level enhancements are detected in the registered muon
flux. A selection of recent events will be presented and compared to data from
the Jungfraujoch neutron monitor. The data of the Karlsruhe Muon Telescope help
to extend the knowledge about Forbush decreases and ground level enhancements
to energies beyond the neutron monitor regime.Comment: 9 pages, 7 figures, in Press AS
Deconvolution of Interplanetary Transport of Solar Energetic Particles
We address the problem of deconvolving the effects of interplanetary
transport on observed intensity and anisotropy profiles of solar energetic
particles with the goal of determining the time profile and spectrum of
particle injection near the Sun as well as the interplanetary scattering mean
free path. Semi-automated techniques have been developed to quantitatively
determine the best fit injection profile, assuming (1) a general piecewise
linear profile or (2) a Reid profile of the form
[C/(t-t_0)]exp[-A/(t-t_0)-(t-t_0)/B]. The two assumptions for the form of the
injection profile yielded similar results when we tested the techniques using
ISEE 3 proton data from the solar flare events of July 20, 1981 (gradual
flare), and January 2, 1982 (impulsive flare). For the former event, the
duration of injection was much shorter for protons of higher energy (75-147
MeV), which may be interpreted as indicating that the coronal mass
ejection-driven shock lost the ability to accelerate protons to 100 MeV
after traveling beyond a certain distance from the Sun.Comment: 14 pages + 5 figures, LaTeX style files included, to appear in J.
Geophys. Re
Simulating Heliospheric and Solar Particle Diffusion using the Parker Spiral Geometry
Cosmic Ray transport in curved background magnetic fields is investigated
using numerical Monte-Carlo simulation techniques. Special emphasis is laid on
the Solar system, where the curvature of the magnetic field can be described in
terms of the Parker spiral. Using such geometries, parallel and perpendicular
diffusion coefficients have to be re-defined using the arc length of the field
lines as the parallel displacement and the distance between field lines as the
perpendicular displacement. Furthermore, the turbulent magnetic field is
incorporated using a WKB approach for the field strength. Using a test-particle
simulation, the diffusion coefficients are then calculated by averaging over a
large number of particles starting at the same radial distance from the Sun and
over a large number of turbulence realizations, thus enabling one to infer the
effects due to the curvature of the magnetic fields and associated drift
motions.Comment: accepted for publication at Journal of Geophysical Research - Space
Physic
The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event
We investigate multi-spacecraft observations of the January 17, 2010 solar
energetic particle event. Energetic electrons and protons have been observed
over a remarkable large longitudinal range at the two STEREO spacecraft and
SOHO suggesting a longitudinal spread of nearly 360 degrees at 1AU. The flaring
active region, which was on the backside of the Sun as seen from Earth, was
separated by more than 100 degrees in longitude from the magnetic footpoints of
each of the three spacecraft. The event is characterized by strongly delayed
energetic particle onsets with respect to the flare and only small or no
anisotropies in the intensity measurements at all three locations. The presence
of a coronal shock is evidenced by the observation of a type II radio burst
from the Earth and STEREO B. In order to describe the observations in terms of
particle transport in the interplanetary medium, including perpendicular
diffusion, a 1D model describing the propagation along a magnetic field line
(model 1) (Dr\"oge, 2003) and the 3D propagation model (model 2) by (Dr\"oge et
al., 2010) including perpendicular diffusion in the interplanetary medium have
been applied, respectively. While both models are capable of reproducing the
observations, model 1 requires injection functions at the Sun of several hours.
Model 2, which includes lateral transport in the solar wind, reveals high
values for the ratio of perpendicular to parallel diffusion. Because we do not
find evidence for unusual long injection functions at the Sun we favor a
scenario with strong perpendicular transport in the interplanetary medium as
explanation for the observations.Comment: The final publication is available at http://www.springerlink.co
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