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B. J. Lynch (Univ. of Michigan / Naval Research Lab), J. R. Gruesbeck, T. H. Zurbuchen (Univ. of Michigan), S. K. Antiochos (Naval Research Lab / Univ. of Michigan)
Nine years of magnetic clouds (MCs) from the WIND and ACE spacecraft (1995-2003) are analyzed using the static, linear, force-free cylinder model. The net cumulative helicity is defined as the difference between the running totals of right- and left-handed MC helicities calculated from the model. This net helicity is a time-dependent quantity that appears to be approximately sinusoidal with a solar cycle like period. There is a right-handed bias in the helicity carried by MCs during solar minimum, and much stronger left-handed bias in the helicity transported during the rising phase and solar maximum, even though there are not drastic differences in the overall number of right- and left-handed clouds. The Bastille Day 2000 MC event is the largest contributor to this left-handed transition.
Monte Carlo simulations of random magnetic cloud sequences from the observed helicity distribution show that the magnitude of the observed left-handed net helicity bias during solar maximum is only expected 2-4 % of the time if right- and left-handed events are equally likely. Possible sources of CME helicity are discussed.
This work is supported by NASA, ONR, and NSF. BJL is supported by a NASA GSRP fellowship NGT5-50453.
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Bulletin of the American Astronomical Society, 36 #2
© YEAR. The American Astronomical Soceity.