Abstract
Abstract. We report recent observations of energetic particles at energies 1–40 MeV/n made by the COSPIN/LET instrument onboard the Ulysses spacecraft during the period of intense solar activity in August/September 2005 during the declining phase of solar cycle 23. Ulysses, having started its climb to high southern latitudes for the third time, was located at ~5 AU, at a helio-latitude of ~30 degrees south. It detected the arrival of a solar wind compound stream resulting from the merging of a series of fast halo CMEs ejected from the Sun in late August and early September 2005 and their interaction with the pre-existing pattern of solar wind Stream Interaction Regions (SIRs) in the ambient medium through which they propagated. The heavy ion intensities are observed by COSPIN/LET to remain elevated for at least 20 days following the very intense X17.0/3B solar flare on 7 September and its associated very fast CME (plane of sky projected CME speed ~2400 km s−1). We carry out an analysis of the composition of the particle increases observed at the location of the spacecraft. Although the composition signatures were predominantly Solar Energetic Particle (SEP)-like, after the passage of the compound stream over Ulysses, in association with a characteristic forward and reverse shock pair, the observations showed evidence of an enhanced He content.
Highlights
Ulysses is the first spacecraft ever to fly over the poles of the Sun
The position of Ulysses on DOY 230, 250 and 272 of 2005 acteristics is observed by Ulysses and strongly suggests that with respect to the fixed Sun-Earth line, projected (a) on the solar during this period, Ulysses detected a system of solar wind equatorial plane as viewed from the north, and (b) on a plane transient flows that resulted from the interaction and merginFgigure 3.pTerhpeepnodsiitciuonlaorftUo ltyhsesessoolnarDeOqYua2t3o0r,a2s5v0iaenwde2d72froofm20t0h5ewEiathrtrhestpoewctatrodthe fixed of the fast backside halo Coronal Mass Ejections (CMEs) ejected from the Sun from 2S9un-EartthhelinSeu, npr(objeocttteodm(a))isonshthoewsno.laAr elqsouastohroiawlnplasnedaasshveiedwbelduferolminethseanreorthe(top), and August (DOY 241) till 5 September (DOY 248) 2005 (Ta(b-) on aidpleaanleApercrpheinmdeicduelasrstpoirtahle msoalagrneeqtiucatfioerlads lvinieewsecdofnrnomecttihnegEUarltyhstsoewsatrod the Sun ble 1)
We report on unique observations obtained from the Cosmic Ray and Solar Particle Investigation (COSPIN)/Low Energy Telescope (LET) instrument onboard the Ulysses spacecraft at an intermediate latitude of 30◦ S and ∼5 AU heliocentric distance during the recent August–September 2005 period of intense solar activity which occurred during the declining phase of the solar cycle 23
Summary
Ulysses is the first spacecraft ever to fly over the poles of the Sun. Following aphelion passage in June 2004, it began its third climb to high southern heliographic latitudes, during the declining phase of solar cycle 23. Hofer et al (2003a, b) investigated the origin of the energetic particle populations during and after the second socalled Fast Latitude Scan (that occurred from 27 November 2000 to 13 October 2001) using elemental composition measurements from the Ulysses/COSPIN/LET. We present recent unique energetic particle measurements in the 1–40 MeV/n range obtained by the COSPIN/LET instrument onboard Ulysses during the August/September 2005 period of intense solar activity, observed during the declining phase of the solar cycle 23.
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