07/23/2012 23:00:00 UTC

This was the famous energetic, very fast event directed at STEREO-A. There were two consecutive prominence eruption/flares starting about 02:20 UT on July 23, seen best in SOHO and STEREO-B observations. The shock hit STEREO-A on July 23, 20:55 UT, followed by two ICMEs, the first starting about 23:00 UT and the second at 01:51 UT on July 24.

- N. Nitta says “It was not an Earth-affecting event, but it was said to have possibly been as geoeffective as the Carrington event had it occurred 9 days earlier [and been aimed at Earth-DW]. I think it is important to understand the interplanetary conditions as disturbed by AR 11520 over an extended period.”

- M. Temmer: “i am currently working together with Nariaki on the complex (two-step) eruption from July 23, 2012 event aiming to simulate the short arrival time and high impact speed by using the analytical drag-based-model. the low density in interplanetary space as well as the high mass of the CME might be the decisive factors for this event to be so fast. The question remains whether the event from July 19 is able to lower the density over several days and as such is able to change the interplanetary conditions. i had during the process of the analysis nice discussions with Ying Liu and Janet Luhmann. We would like to encourage people to take a closer look on this event. We had subjective interpretations of the white-light structures, but most important found no conclusion on the high magnetic field as measured in-situ for both magnetic structures. Is it maybe something intrinsic to the active region? … it would be good to get modelers involved for gaining some deeper insight into the complex eruption process and its in-situ effects.”

[Added by D. Webb]

REFERENCES: Russell, C. et al., ApJ, 770, 38, 2013; Ngwira, C. et al., GRL, 2013; Baker, D., Space Weather, 11, 585, 2013; Liu, D.L. et al., Nature Comm., 5, 4381, 2014.