Bremen 2000 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
EP: Extraterrestrische Physik
EP 9: Sonne und Heliosph
äre III
EP 9.9: Vortrag
Mittwoch, 22. März 2000, 18:00–18:15, H1
Cosmic Rays, the Heliospheric Shield and the Climate on Earth — •K. Scherer1, H. Fichtner2, and O. Stawicki2 — 1dat-hex, Katlenburg-Lindau, Germany — 2Ruhr-Universität Bochum, Germany
The Earth is protected from extraterrestrial influences by three shields: the atmosphere, the magnetosphere, and the heliosphere. The latter, with an extent of about 100-200 astronomical units (1 AU ≈ 149.6 Gm) refers to the circumsolar space filled by the expanding solar atmosphere (solar wind plasma) and prevents a direct contact of Earth with the interstellar medium (ISM). In particular, it serves as a (partially permeable) shield for cosmic rays (CRs) with kinetic energies below ∼ 5 GeV. As a result, the flux of these high energy particles decreases from the heliospheric boundary towards the Earth. A density increase in the local ISM would cause the heliosphere to shrink, i.e. the heliospheric shield to weaken, and, consequently, the CR flux to increase, especially in the lower energy range (< 1 GeV/nucleon). As was shown recently, the CR flux variations due to solar activity (for particle energies > 100 MeV/nucleon by up to a factor three) are correlated with the Earth’ cloud coverage, possibly causing small temperature variations on Earth. An increase of the total number density of the local ISM from the present value of about 0.1 to 1.0 hydrogen atoms/ccm would cause the heliosphere to shrink by a factor of two to three and lead to a 10- to 50-fold increase of the CR flux on Earth. Therefore, a changing interstellar environment leads, most probably to high terrestrial cloudiness on very long time-scales. Thus, changes in the number density of the local ISM can have significant consequences for the Earth’ environment (e.g., triggering of ice ages).