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Ann. Geophys., 24, 785-789, 2006
www.ann-geophys.net/24/785/2006/
© European Geosciences Union 2006
Alfvénic turbulence in solar wind originating near coronal hole boundaries: heavy-ion effects?
B. Bavassano1, N. A. Schwadron2, E. Pietropaolo3, and R. Bruno1
1Istituto di Fisica dello Spazio Interplanetario, Istituto Nazionale di Astrofisica, Rome, Italy
2Department of Astronomy, Boston University, Boston, Massachusetts, USA
3Dipartimento di Fisica, Università di L’Aquila, L’Aquila, Italy
Abstract. The mid-latitude phases of the Ulysses mission offer an excellent opportunity
to investigate the solar wind originating near the coronal hole boundaries.
Here we report on Alfvénic turbulence features, revealing a relevant
presence of in-situ generated fluctuations, observed during the wind
rarefaction phase that charaterizes the transition from fast to slow wind.
Heavy-ion composition and magnetic field measurements indicate a strict time
correspondence of the locally generated fluctuations with 1) the crossing of
the interface between fast and slow wind and 2) the presence of strongly
underwound magnetic field lines (with respect to the Parker spiral). Recent
studies suggest that such underwound magnetic configurations correspond to
fast wind magnetic lines that, due to footpoint motions at the Sun, have
their inner leg transferred to slow wind and are stretched out by the
velocity gradient. If this is a valid scenario, the existence of a magnetic
connection across the fast-slow wind interface is a condition that, given the
different state of the two kinds of wind, may favour the development of
processes acting as local sources of turbulence. We suggest that heavy-ion
effects could be responsible of the observed turbulence features.
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