RADIAL EVOLUTION OF A MAGNETIC CLOUD: MESSENGER , STEREO , AND VENUS EXPRESS OBSERVATIONS
|Author||Good, S.; Forsyth, R.; Raines, J.; Gershman, D.; Slavin, J.; Zurbuchen, T.;|
|Keywords||magnetic fields; parker solar probe; Solar Probe Plus; Solar wind; Sun: coronal mass ejections: CMEs; Sun: heliosphere|
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\textemdashnamely, those provided by MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and Venus Express\textemdashfor 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\textquoterights flux rope has been analyzed using force-free fitting; the rope diameter increased from 0.18 to 0.41 AU (corresponding to an rH0.94 dependence on heliocentric distance, rH), and the axial magnetic field strength dropped from 46.0 to 8.7 nT (an rH-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\textquoterights angular width by assuming helicity conservation. It has also been found that the rope axis rotated by 30\textdegree 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.
|Year of Publication||2015|
|Journal||The Astrophysical Journal|
|Number of Pages||177|