Modeling of magnetic cloud expansion
Astronomical Institute of the Czech Academy of
Sciences, Boční II
1401, 141 00
Praha 4, Czech Republic
2 University Park, LSC, Houston, TX 77070, USA
3 Physics Department, Nuclear and Particle Physics Section, University of Athens, 15771 Ilissia, Greece
Received: 29 December 2014
Accepted: 8 August 2015
Aims. Magnetic clouds are large interplanetary flux ropes that propagate in the solar wind from the Sun and that expand during their propagation. We check how magnetic cloud models, represented by cylindrical magnetic flux ropes, which include expansion, correspond to in situ observations.
Methods. Spacecraft measurements of magnetic field and velocity components inside magnetic clouds with clearly expressed expansion are studied in detail and fit by models. The models include expanding cylindrical linear force-free flux ropes with circular or elliptic cross sections.
Results. From the period of 1995–2009, 26 magnetic clouds were fit by the force-free model of an expanding circular cylindrical flux rope. Expansion velocity profiles qualitatively correspond to model ones in the majority of cases (81%) and quantitatively in more than half of them (58%). In four cases an elliptic cross section significantly improved a match between observed and modeled expansion velocity profiles.
Conclusions. Analysis of velocity components tests magnetic cloud models more strictly and may reveal information on magnetic cloud shapes.
Key words: solar wind / magnetic fields / magnetohydrodynamics (MHD)
© ESO, 2015