2,356 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
Magnetic field configuration and field-aligned acceleration of energetic ions during substorm onsets
International audienceIn this paper, we present an interpretation of the observed field-aligned acceleration events measured by GEOS-2 near the night-side synchronous orbit at substorm onsets (Chen et al., 2000). We show that field-aligned acceleration of ions (with pitch angle asymmetry) is closely related to strong short-lived electric fields in the Ey direction. The acceleration is associated with either rapid dipolarization or further stretching of local magnetic field lines. Theoretical analysis suggests that a centrifugal mechanism is a likely candidate for the parallel energization. Equatorward or anti-equatorward energization occurs when the tail current sheet is thinner tailward or earthward of the spacecraft, respectively. The magnetic field topology leading to anti-equatorward energization corresponds to a situation where the near-Earth tail undergoes further compression and the inner edge of the plasma sheet extends inwards as close as the night-side geosynchronous altitudes
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
Simultaneous effects on parvalbumin-positive interneuron and dopaminergic system development in a transgenic rat model for sporadic schizophrenia
To date, unequivocal neuroanatomical features have been demonstrated neither for sporadic nor for familial schizophrenia. Here, we investigated the neuroanatomical changes in a transgenic rat model for a subset of sporadic chronic mental illness (CMI), which modestly overexpresses human full-length, non-mutant Disrupted-in-Schizophrenia 1 (DISC1), and for which aberrant dopamine homeostasis consistent with some schizophrenia phenotypes has previously been reported. Neuroanatomical analysis revealed a reduced density of dopaminergic neurons in the substantia nigra and reduced dopaminergic fibres in the striatum. Parvalbumin-positive interneuron occurrence in the somatosensory cortex was shifted from layers II/III to V/VI, and the number of calbindin-positive interneurons was slightly decreased. Reduced corpus callosum thickness confirmed trend-level observations from in vivo MRI and voxel-wise tensor based morphometry. These neuroanatomical changes help explain functional phenotypes of this animal model, some of which resemble changes observed in human schizophrenia post mortem brain tissues. Our findings also demonstrate how a single molecular factor, DISC1 overexpression or misassembly, can account for a variety of seemingly unrelated morphological phenotypes and thus provides a possible unifying explanation for similar findings observed in sporadic schizophrenia patients. Our anatomical investigation of a defined model for sporadic mental illness enables a clearer definition of neuroanatomical changes associated with subsets of human sporadic schizophrenia
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