875 research outputs found
On the Statistical Relationship between CME Speed and Soft X-ray Flux and Fluence of the Associated Flare
Both observation and theory reveal a close relationship between the
kinematics of coronal mass ejections (CMEs) and the thermal energy release
traced by the related soft X-ray (SXR) emission. The major problem of empirical
studies of this relationship is the distortion of the CME speed by the
projection effect in the coronagraphic measurements. We present a re-assessment
of the statistical relationship between CME velocities and SXR parameters,
using the SOHO/LASCO catalog and GOES whole Sun observations during the period
1996 to 2008. 49 events were identified where CMEs originated near the limb, at
central meridian distances between 70 and 85, and had a
reliably identified SXR burst, the parameters of which - peak flux and fluence
- could be determined with some confidence. We find similar correlations
between the logarithms of CME speed and of SXR peak flux and fluence as several
earlier studies, with correlation coefficients of 0.48 and 0.58, respectively.
Correlations are slightly improved over an unrestricted CME sample when only
limb events are used. However, a broad scatter persists. We derive the
parameters of the CME-SXR relationship and use them to predict ICME arrival
times at Earth. We show that the CME speed inferred from SXR fluence
measurements tends to perform better than SoHO/LASCO measurements in the
prediction of ICME arrival times near 1 AU. The estimation of the CME speed
from SXR observations can therefore make a valuable contribution to space
weather predictions.Comment: Solar Physics, in pres
Exploring the capabilities of the Anti-Coincidence Shield of the INTEGRAL spectrometer to study solar flares
INTEGRAL is a hard X-ray/gamma-ray observatory for astrophysics (ESA)
covering photon energies from 15 keV to 10 MeV. It was launched in 2002 and
since then the BGO detectors of the Anti-Coincidence shield (ACS) of the SPI
spectrometer have detected many hard X-ray (HXR) bursts from the Sun, producing
lightcurves at photon energies above ~ 100 keV. The spacecraft has a highly
elliptical orbit, providing a long uninterrupted observing time (about 90% of
the orbital period) with nearly constant background due to the reduction of the
crossing time of the Earth's radiation belts. However, due to technical
constraints, INTEGRAL cannot point to the Sun and high-energy solar photons are
always detected in non-standard observation conditions. To make the data useful
for solar studies, we have undertaken a major effort to specify the observing
conditions through Monte-Carlo simulations of the response of ACS for several
selected flares. We check the performance of the model employed for the
Monte-Carlo simulations using RHESSI observations for the same sample of solar
flares. We conclude that, despite the fact that INTEGRAL was not designed to
perform solar observations, ACS is a useful instrument in solar flare research.
In particular, its relatively large effective area allows the determination of
good-quality HXR/gamma-ray lightcurves for X- and M-class solar flares and, in
some cases, probably also for C-class flares.Comment: 18 pages, 6 figures; Solar Physics 201
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 âą. 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
Catalogue of 55-80 MeV solar proton events extending through solar cycles 23 and 24
We present a new catalogue of solar energetic particle events near the Earth,
covering solar cycle 23 and the majority of solar cycle 24 (1996-2016), based
on the 55-80 MeV proton intensity data gathered by the SOHO/ERNE experiment. In
addition to ERNE proton and heavy ion observations, data from the ACE/EPAM
(near-relativistic electrons), SOHO/EPHIN (relativistic electrons), SOHO/LASCO
(coronal mass ejections, CMEs), and GOES soft X-ray experiments are also
considered and the associations between the particle and CME/X-ray events
deduced to obtain a better understanding of each event. A total of 176 SEP
events have been identified as having occurred during the time period of
interest; their onset and solar release times have been estimated using both
velocity dispersion analysis (VDA) and time-shifting analysis (TSA) for
protons, as well as TSA for near-relativistic electrons. Additionally, a brief
statistical analysis has been performed on the VDA and TSA results, as well as
the X-rays and CMEs associated with the proton/electron events, both to test
the viability of the VDA and to investigate possible differences between the
two solar cycles. We find, in confirmation of a number of previous studies,
that VDA results for protons that yield an apparent path length of 1 AU < s <~
3 AU seem to be useful, but those outside this range are probably unreliable,
as evidenced by the anticorrelation between apparent path length and release
time estimated from the X-ray activity. It also appears that even the
first-arriving energetic protons apparently undergo significant pitch angle
scattering in the interplanetary medium, with the resulting apparent path
length being on average about twice the length of the spiral magnetic field.
The analysis indicates an increase in high-energy SEP events originating from
the far eastern solar hemisphere; e.g., such an event...Comment: 33 pages, 12 figures (2 with multiple image files), 1 appendix as an
external PDF file. Article is in the accepted manuscript/referee (single
column) forma
NMDB@Home: 1st virtual symposium on cosmic ray studies with neutron detectors
An overview on the presentations at the first virtual symposium on cosmic ray studies with neutron detectors is given.
The meeting was held online in July 2020. Neutron detectors on ground are shown to provide significant contributions
to research on interactions of galactic cosmic rays with magnetic fields in the Heliosphere and on the acceleration of
energetic particles, as well as to a growing range of applications, including geophysics and space weather. The advent
of easily accessible databases makes original data easily available to a large user community. The present overview
outlines and introduces the more detailed articles contained in the proceedings
A method for the automated detection of solar radio bursts in dynamic spectra
The variability of the solar corona, including flares and coronal mass ejections, affects the space environment of the Earth (heating and ionization of the atmosphere, magnetic field disturbances, and bombardment by high-energy particles). Electromagnetic emissions are the first signatures of a solar eruptive event which by modifying the electron density in the ionosphere may affect airborne technology and radio communications systems. In this paper, we present a new method to detect automatically radio bursts using data from the Nançay Decametre Array (NDA) in the band 10 MHzâ80 MHz. This method starts with eliminating unwanted signals (Radio-Frequency Interference, RFI and Calibration signals) by analyzing the dynamic spectrum of the signal recorded in time. Then, a gradient median filter is applied to smooth and to reduce the variability of the signal. After denoising the signal, an automated solar radio burst detection system is applied. This system is based on a sequential procedure with adaptive constant-false-alarm rate (CFAR like detector) aimed to extract the spectra of major solar bursts. To this end, a semi-automatic software package is also developed to create a data base of all possible events (type II, III, IV or other) that could be detected and used for our performance assessment
NMDB@Athens: Hybrid symposium on cosmic ray studies with neutron detectors
A brief overview is given regarding the presentations delivered at the NMDB@Athens meeting which was held, in a hybrid fashion, in September 2022. Participants joined both remotely but also physically at the National and Kapodistrian University of Athens, Greece. Unlike traditional cosmic ray meetings and conferences where the focus is mainly on the science related to neutron monitor measurements, the âșNMDB@Athensâč meeting uniquely also addresses hardware issues related to these instruments and, importantly, also databases where different data products can be accessed by a growing and increasingly diverse user base. The present overview outlines and introduces the more detailed articles contained in the proceedings
Solar Particle Radiation Storms Forecasting and Analysis: The HESPERIA HORIZON 2020 Project and Beyond
The rather frequent occurrence, and sometimes long duration, of -
ray events at photon energies above 100 MeV challenges our understanding of
particle acceleration processes at the Sun. The emission is ascribed to pion-decay
photons due to protons with energies above 300 MeV.We study the X-ray and radio
emissions and the solar energetic particles (SEPs) in space for a set of 25 Fermi
-ray events. They are accompanied by strong SEP events, including, in most cases
where the parent activity is well-connected, protons above 300 MeV. Signatures of
energetic electron acceleration in the corona accompany the impulsive and early
post-impulsive -ray emission. -ray emission lasting several hours accompanies
in general the decay phase of long-lasting soft X-ray bursts and decametric-tokilometric
type II bursts. We discuss the impact of these results on the origin of
the -ray events.</p
- âŠ