The Magnetic Helicity Budget of Solar Active Regions and Coronal Mass Ejections 

Alexander Nindos Submitted: 20030526 07:59
We compute the magnetic helicity injected by transient photospheric horizontal flows in 6 solar active regions associated with halo coronal mass ejections (CMEs) that produced major geomagnetic storms and magnetic clouds (MCs) at 1 AU. The velocities are computed using the local correlation tracking (LCT) method. Our computations cover
time intervals of 110150 hours and in 4 active regions the
accumulated helicities due to transient flows are factors of 812 larger than the accumulated helicities due to differential rotation. As has been first pointed out by Demoulin & Berger (2003), we suggest that the helicity computed with the LCT method yields not only the helicity injected from shearing motions but also the helicity
coming from flux emergence. We compare the computed helicities injected into the corona with the helicities carried away by the CMEs using the MC helicity computations as proxies to the CME helicities. If we assume that the length of the MC flux tubes is ell=2 AU then the total helicities injected into the corona are a factor of 2.94 lower than the total CME helicities. If we use the
values of ell determined by the condition for the initiation of the kink instability in the coronal flux rope or ell=0.5 AU then the total CME helicities and the
total helicities injected into the corona are broadly consistent. Our study, at least partially, clears
up some of the discrepancies in the helicity budget of active regions because the discrepancies appearing in our paper are much smaller than the ones reported in previous studies. However they point out the uncertainties in the MC/CME helicity calculations and also the limitations of
the LCT method which underestimates the computed helicities.
Authors: A. Nindos, J. Zhang, H. Zhang
Projects: None

Publication Status: ApJ, in press
Last Modified: 20030526 07:59


