Recurrent CIR-accelerated ions observed by STEREO SEPT

Details Recurrent CIR-accelerated ions observed by STEREO SEPT Recurrent CIR-accelerated ions observed by STEREO SEPT

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jgra..11405101g&link_type=abstract

Journal of Geophysical Research, Volume 114, Issue A5, CiteID A05101

Astronomy and Astrophysics

Astrophysics

6

Interplanetary Physics: Corotating Streams, Interplanetary Physics: Energetic Particles (7514), Solar Physics, Astrophysics, And Astronomy: Coronal Holes, Space Weather: General Or Miscellaneous, Interplanetary Physics: Solar Cycle Variations (7536)

Scientific paper

Fast solar wind streams originating from coronal holes interact with the preceding slow wind, leading to the formation of corotating interaction regions (CIRs) in the interplanetary medium. Near solar minimum CIR-associated shocks become the dominant source of energetic ion increases observed near 1 AU in the energy range between some tens of keV/n and 10 MeV/n. Between March 2007 and February 2008, solar activity remained very low, and only a few minor solar energetic particle events were observed. Under these quiet conditions, recurrent CIR-accelerated ion events were regularly observed by the Solar Electron and Proton Telescope (SEPT) on board the twin STEREO spacecraft. The increasing angular separation between STEREO-A and STEREO-B and observations available from near-Earth spacecraft provide an excellent opportunity for multispacecraft analysis of the CIR-associated particle events in the inner heliosphere during an extended period of low solar activity. The ion energy spectrum in the range of 0.6-2.2 MeV is characterized by a power law with spectral indices around 2.7. Below 0.6 MeV the spectrum is flatter and shows more variability. During near-Earth periods, magnetospheric ion bursts contribute significantly to the observed intensities at low energies. Ballistic back mapping has been used to correlate multipoint in situ measurements and coronal synoptic maps. This made it possible to identify the parent coronal holes and to track the same stream for several consecutive rotations. Discrepancies in the structures and the spectra observed by different spacecraft for the same event are sometimes present. These deviations become more evident as the spatial separation between STEREO-A and STEREO-B increases. Coronal hole evolution, radial and latitudinal separation, and interactions between CIRs and interplanetary coronal mass ejections are found to be the main sources of these differences.

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