TitleRADIAL EVOLUTION OF A MAGNETIC CLOUD: MESSENGER , STEREO , AND VENUS EXPRESS OBSERVATIONS
Publication TypeJournal Article
Year of Publication2015
AuthorsGood, SW, Forsyth, RJ, Raines, JM, Gershman, DJ, Slavin, JA, Zurbuchen, TH
JournalThe Astrophysical Journal
Volume807
Issue2
Pagination177
Date Published07/2015
Keywordsmagnetic fields; parker solar probe; Solar Probe Plus; Solar wind; Sun: coronal mass ejections: CMEs; Sun: heliosphere
Abstract

The Solar Orbiter and Solar Probe Plus missions will provide observations of magnetic clouds closer to the Sun than ever before, and it will be good preparation for these missions to make full use of the most recent in situ data sets from the inner heliosphere—namely, those provided by MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and Venus Express—for magnetic cloud studies. We present observations of the same magnetic cloud made by MESSENGER at Mercury and later by Solar TErrestrial RElations Observatory-B (STEREO-B), while the spacecraft were radially aligned in 2011 November. Few such radial observations of magnetic clouds have been previously reported. Estimates of the solar wind speed at MESSENGER are also presented, calculated through the application of a previously established technique. The cloud's flux rope has been analyzed using force-free fitting; the rope diameter increased from 0.18 to 0.41 AU (corresponding to an {r}{{H}}0.94 dependence on heliocentric distance, rH), and the axial magnetic field strength dropped from 46.0 to 8.7 nT (an {r}{{H}}-1.84 dependence) between the spacecraft, clear indications of an expanding structure. The axial magnetic flux was ̃0.50 nT AU2 at both spacecraft, suggesting that the rope underwent no significant erosion through magnetic reconnection between MESSENGER and STEREO-B. Further, we estimate the change in the cloud's angular width by assuming helicity conservation. It has also been found that the rope axis rotated by 30° between the spacecraft to lie close to the solar equatorial plane at STEREO-B. Such a rotation, if it is a common feature of coronal mass ejection propagation, would have important implications for space weather forecasting.

URLhttp://stacks.iop.org/0004-637X/807/i=2/a=177?key=crossref.a1b49ae2196cca72b5d1ec280eba0793
DOI10.1088/0004-637X/807/2/177
Short TitleApJ


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