Energetic Particle Observations and Propagation in the Three-Dimensional Heliosphere During the 2006 December Events

• Published in: The Astrophysical Journal
• Main Authors: Malandraki, O. E., Marsden, R. G., Lario, D., Tranquille, C., Heber, B., Mewaldt, R. A., Cohen, C. M. S., Lanzerotti, L. J., Forsyth, R. J., Elliott, H. A., Vogiatzis, I. I., Geranios, A.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Astronomical Society 2009
• Subjects: South Pole; South pole
• Online Access: https://doi.org/10.1088/0004-637X/704/1/469

We report observations of solar energetic particles obtained by the HI-SCALE and COSPIN/LET instruments onboard Ulysses during the period of isolated but intense solar activity in 2006 December, in the declining phase of the solar activity cycle. We present measurements of particle intensities and also discuss observations of particle anisotropies and composition in selected energy ranges. Active Region 10930 produced a series of major solar flares with the strongest one (X9.0) recorded on December 5 after it rotated into view on the solar east limb. Located over the South Pole of the Sun, at >72°S heliographic latitude and 2.8 AU radial distance, Ulysses provided unique measurements for assessing the nature of particle propagation to high latitudes under near-minimum solar activity conditions, in a relatively undisturbed heliosphere. The observations seem to exclude the possibility that magnetic field lines originating at low latitudes reached Ulysses, suggesting either that the energetic particles observed as large solar energetic particle (SEP) events over the South Pole of the Sun in 2006 December were released when propagating coronal waves reached high-latitude field lines connected to Ulysses, or underwent perpendicular diffusion. We also discuss comparisons with energetic particle data acquired by the STEREO and Advanced Composition Explorer in the ecliptic plane near 1 AU during this period. © 2009. The American Astronomical Society. Received 14 February 2009, accepted for publication 25 August 2009. Published 23 September 2009. We are thankful to our HI-SCALE colleagues for their support and encouragement. Use of the Ulysses Data System is gratefully acknowledged. The CME catalog used to identify the solar origin of the SEP events is generated and maintained by NASA and the Catholic University of America in co-operation with the Naval Research Laboratory. SOHO is a project of international cooperation between ESA and NASA. We thank Manolis Zoulias for help in producing the final figures. The ...