Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh42b..02w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SH42B-02
Astronomy and Astrophysics
Astrophysics
[7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7519] Solar Physics, Astrophysics, And Astronomy / Flares, [7524] Solar Physics, Astrophysics, And Astronomy / Magnetic Fields, [7526] Solar Physics, Astrophysics, And Astronomy / Magnetic Reconnection
Scientific paper
In a widely-held view of impulsive solar energetic particle (ISEP) events, electrons and ions are accelerated at the site of a solar flare when magnetic energy is released by reconnection. When the reconnection involves some open field lines, those field lines provide a path for energetic particles to escape into the heliosphere, leading to the ISEP events sometimes detected in situ near 1 AU. The very limited spatial and temporal extent of the acceleration and release is thought to imply that these particles should have a relatively narrow spread in heliolongitude, a view that has been supported by several studies (e.g., Reames 1999) correlating in situ detections of ISEPs with the locations of the x-ray flares believed to be associated with their acceleration. Since the commissioning of the two STEREO spacecraft in January 2007, in situ observations of ISEPs have been available near 1 AU from three longitudinal positions, with the ACE-STEREO separations increasing by ˜22o per year. Thus by late 2008 the spacings were ˜2× the rms longitudinal spread of ˜20o inferred from the earlier single spacecraft studies, and multi-spacecraft detections of ISEP events should have been quite improbable. Contrary to these expectations, a multi-spacecraft event was detected in November 2008 (Wiedenbeck et al. 2009), with electrons observed over >80o and 3He over >40o. During the subsequent 2 years additional impulsive ISEP events have been recorded, some with 2- or 3-point detections, as the spacecraft separations have continued to increase. In this talk we will summarize the evidence for broad longitudinal spreads in some ISEP events as observed by the LET, SEPT and SIT instruments on STEREO-A and -B and the ULEIS, SIS, and EPAM instruments on ACE. We have attempted to understand the origin of these large spreads seen by examining potential field source surface (PFSS) model calculations of the solar magnetic field between the photosphere and the source surface at 2.5 solar radii, the radius beyond which the field is treated as being frozen into the solar wind plasma. Such model calculations frequently indicate that open field lines originating near an active region may spread by more than several 10's of degrees before reaching the source surface. We will discuss open field line spreading in PFSS models corresponding to the specific times when we have detections of ISEPs. We will also present results of a statistical study of field line spreading in PFSS model calculations for 2007 through 2010 as a test of the probability that expansion of the open flux tubes in the corona could account for the ISEP observations.
Cohen M. C.
Dresing Nina
Gómez-Herrero Raúl
Haggerty Dennis K.
Mason Glenn M.
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