J. Geophys. Res, 105, 7509 - 7519, 2000
Abstract:
Numerical simulations are presented of the evolution of overexpanding
coronal mass ejections (OCMEs), which are also magnetic clouds. The
OCME is assumed to arise from the evolution of a magnectic flux rope
with high plasma and magnetic pressure and high plasma density near
the Sun in a high-speed solar wind. It is shown that the flux rope
maintains its integrity from near the Sun to around 5 AU, resisting
hydrodynamic forces that tends to distort it. Thus OCMEs that are
magnetic clouds at large heliocentric distance should have simply
evolved from near-Sun flux ropes. It is shown that an initially
circular flux rope is distorted into a hemispheric shape by its
interaction with solar wind plasma flows. Forward and reverse shock
pairs form with the forward shock being curved while the reverse shock
is straight. The magnetic field properties at large distances are
shown to depend on whether the initial flux rope undergoes
overexpansion. A flux rope that is convected passively in the solar
wind without overexpansion will ultimately have a magnetic field
profile dominated by its toroidal component, so would not be observer
as a magnetc cloud. The overexpanding flux ropes modeled here maintain
an approximately equal ratio of toroidal to poloidal magnetic
fields. The relative initial speed of the flux rope with respect to the
solar wind does not influence the large-scale magnetic properties up
to 5 AU, although it does affect the detailed field topology.
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