HR: 16:15h
AN: SH34A-02    [Abstracts]
TI: High Latitude Magnetic Field Polarity Reversals: A Solar Source or In Situ Generation?
AU: Landi, S
EM: slandi@arcetri.astro.it
AF: Dipartimento di Astronomia, Universita` di Firenze, Largo E Fermi 2, Firenze, 50125 Italy
AU: Hellinger, P
EM: Petr.Hellinger@ufa.cas.cz
AF: Dipartimento di Astronomia, Universita` di Firenze, Largo E Fermi 2, Firenze, 50125 Italy
AU: * Velli, M
EM: velli@arcetri.astro.it
AF: Dipartimento di Astronomia, Universita` di Firenze, Largo E Fermi 2, Firenze, 50125 Italy
AU: * Velli, M
EM: velli@arcetri.astro.it
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr, Pasadena, CA 91109 United States
AU: Winterhalter, D
EM: Daniel.Winterhalter@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr, Pasadena, CA 91109 United States
AB: High latitude observations of the magnetic field by the Ulysses spacecraft have shown a significant number of cases where the radial magnetic field polarity is reversed with respect to the dominant polarity of the coronal hole from which the wind emanates. It has been suggested that such reversals are due to reconnection of closed and open field lines in the lower corona which would launch a large amplitude Alfv‚n wave into the solar wind. Here we carry out 2.5D simulations of such a wave and show that the kink in the field line tends to be unstable, disappearing within a few dynamical time-scales. We suggest an alternative mechanism for the generation of polarity reversals, namely, the coupling of standard large amplitude Alfv‚n turbulence propagating away from the sun with the micro-stream shears observed in the high speed solar wind. Numerical simulations show that reversals generated by shears in the wind tend to be stable, and the time-scale required for such generation is compatible with the transport time out to 1 AU and beyond. It remains to be seen whether any correlation between microstream structure and polarity reversals can be found in the Ulysses data.
DE: 7800 SPACE PLASMA PHYSICS
DE: 7827 Kinetic and MHD theory
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting