ALBERT

Description: We examine the magnetic causes of coronal mass ejections (CMEs) by examining, along with the correlations of active-region magnetic measures with each other, the correlations of these measures with active-region CME productivity observed in time windows of a few days, either centered on or extending forward from the day of the magnetic measurement. The measures are from 36 vector magnetograms of bipolar active regions observed within -30" of disk center by the Marshal Space Flight Center (MSFC) vector magnetograph. From each magnetogram, we extract six whole-active-region measures twice, once from the original plane-of-the-sky magnetogram and again a h r deprojection of the magnetogram to disk center. Three of the measures are alternative measures of the total nonpotentiality of the active region, two are alternative measures of the overall twist in the active-region's magnetic field, and one is a measure of the magnetic size of the active region (the active region's magnetic flux content). From the deprojected magnetograms, we find evidence that (1) magnetic twist and magnetic size are separate but comparably strong causes of active-region CME Productivity, and (2) the total free magnetic energy in an active region's magnetic field is a stronger determinant of the active region's CME productivity than is the field's overall twist (or helicity) alone. From comparison of results from the non-deprojected magnetograms with corresponding results from the deprojected magnetograms, we find evidence that (for prediction of active-region CME productivity and for further studies of active-region magnetic size as a cause of CMEs), for active regions within approx.30deg of disk center, active-region total nonpotentiality and flux content can be adequately measured from line-of-sight magnetograms, such as from SOH0 MDI.

Description: To probe the magnetic causes of CMEs, we have examined three types of magnetic measures: size, twist and total nonpotentiality (or total free magnetic energy) of an active region. Total nonpotentiality is roughly the product of size times twist. For predominately bipolar active regions, we have found that total nonpotentiality measures have the strongest correlation with future CME productivity (approx. 75% prediction success rate), while size and twist measures each have a weaker correlation with future CME productivity (approx. 65% prediction success rate) (Falconer, Moore, & Gary, ApJ, 644, 2006). For multipolar active regions, we find that the CME-prediction success rates for total nonpotentiality and size are about the same as for bipolar active regions. We also find that the size measure correlation with CME productivity is nearly all due to the contribution of size to total nonpotentiality. We have a total nonpotentiality measure that can be obtained from a line-of-sight magnetogram of the active region and that is as strongly correlated with CME productivity as are any of our total-nonpotentiality measures from deprojected vector magnetograms. We plan to further expand our sample by using MDI magnetograms of each active region in our sample to determine its total nonpotentiality and size on each day that the active region was within 30 deg. of disk center. The resulting increase in sample size will improve our statistics and allow us to investigate whether the nonpotentiality threshold for CME production is nearly the same or significantly different for multipolar regions than for bipolar regions. In addition, we will investigate the time rates of change of size and total nonpotentiality as additional causes of CME productivity.

Description: We show that the length of strong-gradient, strong-field main neutral line, L(sub SGM), which can be measured from line-of-sight magnetograms such as from SOHO/MDI, is both a measure of active-region nonpotentiality and a useful predictor of an active region's future CME productivity. To demonstrate that L(sub SGM) is a nonpotentiality measure, we show that it is strongly correlated with a direct measure of nonpotentiality. For an appropriate choice of a threshold value, an active region s measured LsGM can be used as a predictor of whether the active region will produce a CME within a few days after the magnetogram. For our set of 36 MSFC vector magnetograms of bipolar active regions, L(sub SGM) is found to have a success rate of 80% for prediction of CME productivity in the 0-2 day window. The development of L(sub SGM) as a method of measuring nonpotentiality for forecasting large, fast CMEs from present space based assets is of value to NASA's Space Exploration Initiative (manned missions to the Moon and Mars)

Description: We report further results from our ongoing assessment of magnetogram-based measures of active-region nonpotentiality and size as predictors of coronal mass ejections (CMEs). We have devised improved generalized measures of active-region nonpotentiality that apply to active regions of any degree of magnetic complexity, rather than being limited to bipolar active regions as our initial measures were. From a set of approx.50 active-regions, we have found that measures of total nonpotentiality have a 75-80% success rate n predicting whether an active region will produce a CME in 2 days after the magnetogram. This makes measures of total nonpotentiality a better predictor than either active-region size, or active region twist (size-normalized nonpotentiality), which have a approx.65% success rates. We have also found that we can measure from the line-of-sight magnetograms an active region's total nonpotentiality and the size, which allows use to use MDI to evaluate these quantities for 4-5 consecutive days for each active region, and to investigate if there is some combination of size and total nonpotentiality that have a stronger predictive power than does total nonpotentiality. This work was funded by NASA through its LWS TR&T Program and its Solar and Heliospheric Physics SR&T Program, and by NSF through its Solar Terrestrial Research and SHINE programs.

Description: From chromospheric and coronal images and line-of-sight and vector magnetograms of magnetic regions that produce CMEs, and from chromospheric and coronal movies of the onsets of CME eruptions, it appears that the magnetic field that explodes to drive the CME is initially the strongly sheared core of a magnetic arcade encasing a polarity dividing line in the magnetic flux. Before or during the onset of the explosion, the sheared core field becomes a flux rope, often carrying chromospheric material within it. For the erupting flux rope to drive the explosion, that is, for its magnetic energy content to decrease in the explosion, the flux rope's cross-sectional area must increase faster than its length. For instance, for isotropic expansion, the area increases as the square of the length, and the magnetic energy content of the flux rope decreases as the inverse of the length. The instability that initiates the eruption of the flux rope might be an ideal MHD kink instability, or might involve runaway tether-cutting reconnection. The reconnection begins below the flux rope (internal to the arcade) when the overall field configuration of the region is effectively that of a single bipole. When the flux rope resides in a multi- bipolar configuration having a magnetic null above the flux rope, the runaway tether- cutting reconnection might begin either below the flux rope or at the null above (external to) the arcade. We present examples of observed CME onsets that illustrate the above alternatives. In each example, reconnection below the flux rope begins early in the eruption. This indicates that internal tether cutting reconnection (classic tether-cutting reconnection) is important in unleashing the CME explosion in all cases, including those in which the explosion may be triggered by MHD kinking or by external reconnection (classic breakout reconnection).