Freiburg 2008 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

EP: Fachverband Extraterrestrische Physik

EP 4: The Sun and Heliosphere - Poster Session

EP 4.16: Poster

Montag, 3. März 2008, 17:30–19:00, Vorraum KGI-Aula

Ulysses observations of recurrent cosmic ray decreases during solar cycle 22 and 23 — •Phillip Dunzlaff, Bernd Heber, Oliver Rother, Reinhold Müller-Mellin, Andreas Klassen, Raul Gomez-Herrero, and Robert Wimmer-Schweingruber — IEAP, Christian-Albrechts-Universität Kiel, Germany

During the first south polar pass of the Ulysses spacecraft from mid-1992 to mid-1994 (solar cylce 22), the counting rates of several hundred MeV galatic cosmic rays were modulated by transient and recurrent decreases at all latitudes. In solar cycle 23, from late 2004 to 2007 the Ulysses spacecraft repeated this trajectory segment during a similar phase of the solar cycle but with the opposite heliospheric magnetic field polarity. In this contribution we determine the amplitude and latitude distribution of recurrent cosmic ray decreases in solar cycle 22 and 23: 1. While recurrent cosmic ray decreases were present up to highest latitudes in the 1990’s, we find that recurrent cosmic ray decreases vanish above 40^∘ S in 2006. 2. A spectral analysis on the solar wind speed and the magnetic field strength leads to a 26 and 24.5-day periodicity in cycle 22 and 23, respectively. While the 26-day variation continues to highest latitudes the 24.5 days vanishes in the fast solar wind regime. Thus we suggest tentatively that the difference between solar cycle 22 and 23 is caused by a different coronal structure, as observed in coronal maps. While the 1990’s recurrent decreases are caused by the large extension of the southern polar coronal hole towards low latitudes the decreases in the 2000’s are due to relatively stable, ”small” equatorial coronal holes.