associated to Stealth CMEs Mathematisch-Naturwissenschaftliche Fakultät Forbush decreases associated to Stealth CMEs B. Heber, D. Galsdorf, J. Gieseler, K. Herbst, P. Kühl, Christian-Albrechts-Universität zu Kiel M.Dumbović, B. Vršnak, HVAR Observatory Zagreb A. Veronic, M. Temmer, and C. Moestl, University of Graz, Austria
Zusammenfassung Forbush decreases associated with an ICME Mathematisch-Naturwissenschaftliche Fakultät Zusammenfassung Upper panel:Schematic of an interplanetary coronal mass ejection driving a sheath region ahead of it. Lower panel: Time profiles of Forbush decreases depending on the spacecraft trajectory through the ICME: (A) Crossing of sheath and ejecta (B) Crossing of sheath only (from Richardson and Cane, 2011)
Zusammenfassung Stealth CMEs Mathematisch-Naturwissenschaftliche Fakultät Zusammenfassung CMEs have low corona signatures: flares, filament eruption, coronal waves and dimming’s. “Stealth” CMEs do not have these attributes: harder to detect on the disk? But signature in coronagraphs
Zusammenfassung Stealth CMEs Mathematisch-Naturwissenschaftliche Fakultät Zusammenfassung Typical Amplitude <1%. What kind of instrument is needed? Neutron Monitors are high statistical significant counters Neutron Monitors are not suited for low amplitude decreases because: Of the daily variation and other magnetospheric effects. Of their energy response ascribed by the yield function Utilize SOHO and Chandra single counter measurements.
... not only … but also being out of the Earth magnetosphere Mathematisch-Naturwissenschaftliche Fakultät Zusammenfassung S/C Neutron monitors
Classes of FDs observed with stealth CMEs Mathematisch-Naturwissenschaftliche Fakultät Zusammenfassung Classical two step - Forbush Decreasce MC - dominated FD
Zusammenfassung Results Mathematisch-Naturwissenschaftliche Fakultät Zusammenfassung Nr. 1 2 3 4 5 6 7 8 9 10 11 FD/% 3.1 * 1.7 1.3 0.9 0.7 1.0 3.3 For two events (3) and (5) SOHO did not transmit data. For all other events SOHO / EPHIN measured a Forbush Decrease Although events are associated with stealth CMEs two types of FDs are observed.