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Modern Solar Facilities – Advanced Solar Science, 257–260 F. Kneer, K. G. Puschmann, A. D. Wittmann (eds.) c  Universitätsverlag Göttingen 2007 Evolution of the photospheric magnetic field in the source regions of coronal mass ejections V. Bothmer1,* and D. Tripathi2 1 Institut für Astrophysik, Göttingen, Germany 2 Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom * Email: bothmer@astro.physik.uni-göttingen.de Abstract. Six coronal mass ejections associated with erupting quiescent filaments on the visible solar disk were identified in data from SoHO (Solar and Heliospheric Observatory) LASCO (Large Angle and Spectrometric Coronagraph), EIT (Extreme ultraviolet Imaging Telescope) and MDI (Michelson Doppler Imager) data and ground-based Hα observations from Big Bear and Meudon observatories. These events were analysed to investigate whether their initiations could be related to changes of the underlying photospheric field. The results show that in five out of the six events, substantial changes in the photospheric magnetic field occurred in the source regions prior and around the CME’s lift-off times as identified from emerging/diminishing flux detected by MDI. In one event large magnetic flux changes could be identified not in the source region itself, but in a neighbouring active region. The results demonstrate that new missions, such as STEREO and Hinode (Solar-B) in conjunction with SoHO and ground-based measurements, will provide joint data sets that have the potential to provide new insight into the physical causes of CMEs. 1 Introduction Large-scale transient releases of solar matter into interplanetary space occur in the form of coronal mass ejections (CMEs) (e.g., Hundhausen 1999). CMEs are the causes of interplanetary shock waves, large-scale disturbances of the heliosphere, major geomagnetic storms and solar energetic particle events (Webb 2000, Bothmer 1999, 2003). The physical causes of CMEs are not understood so far and a variety of theoretical models exist having their own advantages and drawbacks (e.g., Lin et al. 2003, Aschwanden 2004). CMEs are often associated with the disappearance of a filament, as visible in Hα, EUV and micro-wave observations (e.g., Bothmer & Rust 1997, Bothmer & Schwenn 1998, Gopalswamy et al. 2003, Tripathi et al. 2004). Rather few studies have been undertaken so far using simultaneous space- and groundbased multi-wavelength observations (e.g., Song et al. 2002). A study based on the combined analysis of coronal and photospheric data suggests that newly emerging magnetic flux in the photosphere can lead to the onset of a CME if the flux has a magnetic polarity which is favourable for magnetic reconnection with the pre-existing field near the filament site (Feynman & Martin 1995). However, it seems that eruptions can also occur in the absence of any observable flux emergence (Wang & Sheeley 1999). In addition to the scenario of 258 Bothmer and Tripathi: Magnetic flux in source region of CMEs emerging flux, cancellation of photospheric magnetic flux has also been suggested as a trigger for prominence eruptions and CMEs (e.g., Linker et al. 2003). Alternatively, CMEs may be caused by large-scale instabilities of the corona, as in the case of instabilities of trans-equatorial loops connecting different active regions (e.g., Zhou et al. 2005). In a detailed analysis of SoHO data Tripathi et al. (2004) and Tripathi (2005) found that transient post-eruptive arcades (PEAs) visible at EUV-wavelengths can be considered as unique tracers of CMEs on the solar disk. From the database1 of this study we have selected those CME events which were associated with disappearing filaments exceeding heliographic lengths of 10 degrees. Our set of six events comprises CMEs associated with quiescent filaments from decaying active regions with less complex magnetic field structures, contrary to the study of CMEs from active regions by Muglach & Dere (2005). The less complex magnetic structure is useful for unambiguous interpretation of the data. With our selection criterium we tried to minimize the problem of making false associations between coronal and photospheric changes because the photospheric flux is ever varying on different spatial- and time-scales, e.g., as visible from the observations of the small-scale bipoles of the magnetic carpet, the appearances of X-ray bright points and active regions or the large changes apparent in sunspot groups. 2 Data For the present study, data from SoHO/LASCO/EIT/MDI (Fleck et al. 1995) were used. Complementary, Hα ground-based data from Paris/Meudon2 and Big Bear3 were studied. The source regions of the six selected CME...

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