40 research outputs found
Abundances of Suprathermal Heavy Ions in CIRs during the Minimum of Solar Cycle 23
In this paper we examine the elemental composition of the 0.1-1 MeV/nucleon
interplanetary heavy ions from H to Fe in corotating interaction regions (CIRs)
measured by the SIT (Suprathermal Ion Telescope) instrument. We use
observations taken on board the STEREO spacecraft from January 2007 through
December 2010, which included the unusually long solar minimum following solar
cycle 23. During this period instruments on STEREO observed more than 50 CIR
events making it possible to investigate CIR ion abundances during solar
minimum conditions with unprecedented high statistics. The observations reveal
annual variations of relative ion abundances in the CIRs during the 2007-2008
period as indicated by the He/H, He/O and Fe/O elemental ratios. We discuss
possible causes of the variability in terms of the helium focusing cone passage
and heliolatitude dependence. The year 2009 was very quiet in CIR event
activity. In 2010 the elemental composition in CIRs were influenced by sporadic
solar energetic particle (SEP) events. The 2010 He/H and He/O abundance ratios
in CIRs show large event to event variations with values resembling the
SEP-like composition. This finding points out that the suprathermal SEPs could
be the source population for CIR acceleration.Comment: accepted for publication in Solar Physic
3He-rich SEP Events Observed by STEREO-A
Using the SIT (Suprathermal Ion Telescope) instrument on STEREO-A we have
examined the abundance of the rare isotope 3He during the rising activity phase
of solar cycle 24 between January 2010 and December 2011. We have identified
six solar energetic particle (SEP) events with enormous abundance enhancements
of 3He (3He/4He >1). The events were short lasting, typically ~0.5-1 day and
most of them occurred in association with high-speed solar wind streams and
corotating interaction regions. With one exception the events were not
associated with ~100 keV solar electron intensity increases. The events showed
also enhanced NeS/O and Fe/O ratios. The solar images indicate that the events
were generally associated with the active regions located near a coronal hole.Comment: accepted for publication in AIP Conference Proceedings for
'Thirteenth International Solar Wind Conference
Energy spectra of 3He-rich solar energetic particles associated with coronal waves
In addition to their anomalous abundances, 3He-rich solar energetic particles
(SEPs) show puzzling energy spectral shapes varying from rounded forms to power
laws where the later are characteristics of shock acceleration. Solar sources
of these particles have been often associated with jets and narrow CMEs, which
are the signatures of magnetic reconnection involving open field. Recent
reports on new associations with large-scale EUV waves bring new insights on
acceleration and transport of 3He-rich SEPs in the corona. We examined energy
spectra for 32 3He-rich SEP events observed by ACE at L1 near solar minimum in
2007-2010 and compared the spectral shapes with solar flare signatures obtained
from STEREO EUV images. We found the events with jets or brightenings tend to
be associated with rounded spectra and the events with coronal waves with power
laws. This suggests that coronal waves may be related to the unknown second
stage mechanism commonly used to interpret spectral forms of 3He-rich SEPs.Comment: Presented at 15th Annual International Astrophysics Conference "The
Science of Ed Stone". Accepted for publication in Journal of Physics:
Conference Serie
Multi-Spacecraft Observations of Recurrent 3He-Rich Solar Energetic Particles
We study the origin of 3He-rich solar energetic particles (<1 MeV/nucleon)
that are observed consecutively on STEREO-B, ACE, and STEREO-A spacecraft when
they are separated in heliolongitude by more than 90{\deg}. The 3He-rich period
on STEREO-B and STEREO-A commences on 2011 July 1 and 2011 July 16,
respectively. The ACE 3He-rich period consists of two sub-events starting on
2011 July 7 and 2011 July 9. We associate the STEREO-B July 1 and ACE July 7
3He-rich events with the same sizeable active region producing X-ray flares
accompanied by prompt electron events, when it was near the west solar limb as
seen from the respective spacecraft. The ACE July 9 and STEREO-A July 16 events
were dispersionless with enormous 3He enrichment, lacking solar energetic
electrons and occurring in corotating interaction regions. We associate these
events with a small, recently emerged active region near the border of a
low-latitude coronal hole that produced numerous jet-like emissions temporally
correlated with type III radio bursts. For the first time we present
observations of 1) solar regions with long-lasting conditions for 3He
acceleration and 2) solar energetic 3He that is temporary
confined/re-accelerated in interplanetary space.Comment: accepted for publication in The Astrophysical Journa
Interpretation of increased energetic particle flux measurements by SEPT aboard the STEREO spacecraft and contamination
Context. Interplanetary (IP) shocks are known to be accelerators of energetic
charged particles observed in-situ in the heliosphere. However, the
acceleration of near-relativistic electrons by shocks in the interplanetary
medium is often questioned. On 9 August 2011 a Corotating Interaction Region
(CIR) passed STEREO B (STB) that resulted in a flux increase in the electron
and ion channels of the Solar Electron and Proton Telescope (SEPT). Because
electron measurements in the few keV to several 100 keV range rely on the
so-called magnet foil technique, which is utilized by SEPT, ions can contribute
to the electron channels. Aims. We aim to investigate whether the flux increase
in the electron channels of SEPT during the CIR event on 9 August 2011 is
caused by ion contamination only. Methods. We compute the SEPT response
functions for protons and helium utilizing an updated GEANT4 model of SEPT. The
CIR energetic particle ion spectra for protons and helium are assumed to follow
a Band function in energy per nucleon with a constant helium to proton ratio.
Results. Our analysis leads to a helium to proton ratio of 16.9% and a proton
flux following a Band function with the parameters /
(cm2 s sr MeV/nuc.), keV/nuc. and spectral indices of and which are in good agreement with measurements by
the Suprathermal Ion Telescope (SIT) aboard STB. Conclusions. Since our results
explain the SEPT measurements, we conclude that no significant amount of
electrons were accelerated between keV and keV by the CIR