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Astron. Astrophys. 356, 315-318 (2000)

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An estimation of the shape and temporal variation of the solar wind sonic, Alfvénic and fast magnetosonic surfaces

G. Exarhos and X. Moussas

Section of Astrophysics, Astronomy and Mechanics, Physics Department, National University of Athens, Panepistimiopolis GR 15783, Zografos, Athens, Greece

Received 10 March 1999 / Accepted 27 January 2000


In this work we find the shape and dimension of the solar wind transition surfaces, namely the slow (sonic), the fast magnetosonic and the Alfvén surface, as a function of heliospheric latitude using actual experimental data from Ulysses spacecraft during its first pole to pole journey. We also give the temporal variation of the radius of these surfaces using measurements from spacecraft at 1 AU. All transition surfaces are equatorial elongated. The sonic surface is the most asymmetric surface with polar radius [FORMULA] and equatorial radius [FORMULA]. The Alfvén and the fast magnetosonic surfaces seems to be less asymmetric. The Alfvén polar and equatorial radius is [FORMULA] and [FORMULA] respectively while the fast magnetosonic polar and equatorial radius is [FORMULA] and [FORMULA] respectively. The temporal variation of the transition surfaces radii follows the 11-year solar cycle except for the sonic radius which seems not to vary remarkably with time.

Key words: hydrodynamics – Sun: solar wind

Send offprint requests to: X. Moussas

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000