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It is paramount from both scientific and societal perspectives to understandthe generation of extreme space weather. We discuss the formation of solarsuperstorms based on a comparative study of the 2012 July 23 and 2017 July 23eruptions. The first one is Carrington-class, and the second could rival the1989 March event that caused the most intense geomagnetic storm of the spaceage. Observations of these events in the historically weak solar cycle 24indicate that a solar superstorm can occur in any solar cycle and at any phaseof the cycle. Recurrent patterns are identified in both cases, including thelong-lived eruptive nature of the active region, a complex event composed ofsuccessive eruptions from the same active region, and in-transit interactionbetween the successive eruptions resulting in exceptionally strong ejectamagnetic fields at 1 AU. Each case also shows unique characteristics.Preconditioning of the upstream solar wind leading to unusually high solar windspeeds at 1 AU is observed in the first case whereas not in the latter. Thismay suggest that the concept of "preconditioning" appears to be necessary formaking a Carrington-class storm. We find a considerable deflection by nearbycoronal holes in the second case but not in the first. On the basis of theseresults, we propose a hypothesis for further investigation that superstorms are"perfect storms" in nature, i.e., a combination of circumstances that resultsin an event of unusual magnitude. Historical records of some extreme eventsseem to support our hypothesis.

A Comparative Study of 2017 July and 2012 July Complex Eruptions: Are Solar Superstorms "Perfect Storms" in Nature?