THE ESCAPE OF MAGNETIC-FLUX FROM THE SUN

.Analysis of heliospheric magnetic fields at 1 AU shows that 10(24) Mx of net azimuthal flux is ejected by the Sun per solar cycle. This rat e is identified with the rate of toroidal flux generation. It is compa red with indicators of flux ejection from the solar atmosphere, includ ing coronal mass ejections (CMEs), filament eruptions, and active regi on loop expansion. The rate is consistent with estimates of flux escap ing in these phenomena. The toroidal flux escape rate is compared with the apparent rate of flux emergence at the solar surface, and it is c oncluded that escaping toroids will remove at least 20% of the emergin g flux, and probably remove 100% of emerging flux, since multiple erup tions occur on the toroids. The data imply that flux escapes the Sun w ith an efficiency far exceeding Parker's upper limit estimate of 3%. T oroidal flux escape is almost certainly the source of the observed ove rwinding of the interplanetary magnetic field spiral. Two mechanisms t o facilitate net flux escape are discussed: helicity charging to push open the fields and flux transport with reconnection to close them off . We estimate the Sun will shed similar to 2 x 10(45) Mx(2) of magneti c helicity per solar cycle, leading to a mean helicity density of 100 Mx(2) cm(-3) at 1 AU, which agrees well with observations. Helicity sh edding and flux escape are seen as essential to the cyclic renewal of the solar dynamo. It is argued that because left-handed and right-hand ed helical fields accumulate in the northern and southern hemispheres, separately, conservation of magnetic helicity requires that the dynam o-generated fields be expelled. The mean lifetime of magnetic flux on the solar surface is 3-6 months. The mechanisms described here should also enable Sun-like stars to shed dynamo-generated fields.