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We demonstrate that magnetic reconnection is not necessary to initiate fastCMEs. The Aly-Sturrock conjecture states that the magnetic energy of a givenforce free boundary field is maximized when the field is open. This isproblematic for CME initiation because it leaves little or no magnetic energyto drive the eruption, unless reconnection is present to allow some of thefield to escape without opening. Thus, it has been thought that reconnectionmust be present to initiate CMEs. This theory has not been subject to rigorousnumerical testing because conventional MHD numerical models contain numericaldiffusion, which introduces uncontrolled numerical reconnection. We use aquasi-Lagrangian simulation technique to run the first controlled experimentsof CME initiation in the complete lack of reconnection. We find that a fluxrope confined by an arcade, when twisted beyond a critical amount, can escapeto an open state, allowing some of the surrounding arcade to shrink andreleasing magnetic energy from the global field. This mechanism includes a trueideal MHD instability. We conclude that reconnection is not a necessary triggerfor fast CME eruptions.

Reconnectionless CME eruption: putting the Aly-Sturrock conjecture to rest