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Cliver , E. et al. ApJ, 631, 604, 2005 Gopalswamy, N. et al. GRL, 27, 1427, 2000

Solar Sources of Wide Coronal Mass Ejections during the Ascending Phase of Cycle 24. Sachiko Akiyama 1,2 , Nat Gopalswamy 2 , Seiji Yashiro 1,2 , and Pertti Mäkelä 1,2 1 The Catholic University of America, 2 NASA/GSFC, sachiko.akiyama@nasa.gov. Background

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Cliver , E. et al. ApJ, 631, 604, 2005 Gopalswamy, N. et al. GRL, 27, 1427, 2000

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  1. Solar Sources of Wide Coronal Mass Ejections during the Ascending Phase of Cycle 24 Sachiko Akiyama1,2, Nat Gopalswamy2, Seiji Yashiro1,2 ,and Pertti Mäkelä1,2 1The Catholic University of America, 2NASA/GSFC, sachiko.akiyama@nasa.gov Background After the middle of 2010, we have an excellent opportunity to identify the solar sources of CMEs because of the increased data coverage from SDO, SOHO and STEREO. SDO provides high spatial and temporal resolution images compared to previous missions. Multiple views from SOHO and STEREO-A/B enabled us to view the whole solar surface, so it became easy to discriminate between the front and back side CMEs. We examined the solar sources of all wide CMEs (width > 60°) observed by either SOHO/LASCO or STEREO/SECCHI in 2011 (ascending phase of solar cycle 24) with this enhanced observing capability in order to clarify some results from the previous solar cycle. Solar Sources Solar eruptive phenomenasuch as active region flares, eruptive filaments, and coronal dimming are well known signatures indicative of CME solar sources. Out of the 597 wide CMEs, 322 (54%) were associated with active region flares and 164 (27%) with eruptive quiescent prominences (EPs). In 88 cases (15%) only EUV dimmings (DIMs) were observed. For the remaining 23 (4%) of CMEs we were not able to identify the solar sources, i.e. they are stealth CMEs (Wagner, 1984; Robbrect et al. 2009). Table 2 – Solar Sources of the CMEs FL: Flare; EP: Eruptive quiescent Prominence; DIM: Dimming; UNK: Unknown Visibility of CMEs Since coronagraphs detect the Thomson-scattered photospheric light, a CME might not be detected when it originates from the disk center. The CME visibility has been examined indirectly using the association of radio bursts (Gopalswamy et al. 1999), flares (Yashiro et al. 2005), and EUV waves (Cliver et al. 2005). Thanks to the side view provided by STEREO, we have the opportunity to investigate the CME visibility directly. We consider 597 wide CMEs observed by either SOHO/LASCO or STEREO/COR1. We examine whether the CMEs observed by SOHO/LASCO are also observed by STEREO/COR1, and vice versa. We found that 535 (or 90%) out of the 597 wide CMEs are detected by all coronagraphs. However the remaining 10% of wide CMEs are not observed by all coronagraphs (see Table 1 for details). Table 1 – Visibility of the CMEs. FS: Frontside; BS: Backside; UNC: Uncertain Fig. 1 shows the source locations of wide CMEs observed by STEREO/COR1 but not observed by SOHO/LASCO (we refer these as STEREO-Only CMEs). As expected, we see that the STEREO-Only CMEs originated near the center of the frontside or backside disk. The speeds of the frontside STEREO-Only CMEs are less than 450 km/s. In other words, LASCO is able to detect all frontside CMEs with speed > 450 km/s and width> 60°. (d) As reported by previous studies (e.g. Gopalswamy 2010), the flare-associated CMEs are fast and wide compared to others (Figs. 2a and 2d). Figures 2b and 2c shows that there are no fast and wide (FW) CMEs (speed>900 km/s and width>60o) associated with the EPs and the DIMs. All FW CMEs originate from ARs and are associated with flares. But the FW CMEs are not exclusively associated with major flares (M and X class). Approximately 30% of the FW CMEs are associated with C-class flares. (a) (c) (a) (e) (b) (d) (f) (b) (c) Fig. 2 – Speed and width distributions of CMEs associated with the flares (top), eruptive quiescent prominences (middle), and dimmings (bottom). Stealth CMEs We found that 4% of wide CMEs are stealth CMEs. The rate is much smaller compared to Ma et al. (2010) who reported that one third of CMEs observed by STEREO/COR2 were not observed by SOHO/LASCO. The primary reason is that we examined only wide CMEs while Ma et al. included narrow CMEs. The speed distribution of the stealth CMEs (Fig. 3b) clearly shows that they are slow. This is consistent with Ma et al., who reported that the average speed of 11 stealth CMEs as 188 km/s. The stealth CMEs are the least energetic population compared to other three groups, as originally reported by Wagner (1984). Fig. 3 – Speed and width distributions of All (top) and Stealth CMEs (bottom). References Cliver, E. et al. ApJ, 631, 604, 2005 Gopalswamy, N. et al. GRL, 27, 1427, 2000 Gopalswamy, N., Proc.20th NSPM, 108, 2010 Ma, S. et al. ApJ, 722, 289-301, 2010 Robbrecht, E. et al., ApJ, 701, 283, 2009 Wagner, W. J. ARAA 22, 267, 1984 Yashiro, S. et al. 2005, JGR 110, A12S05, 2005 Fig. 1 - Source Locations of STEREO-Only CMEs. The circle size indicates the CME speed.

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