科研之友
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摘要
We compare the geoeffective parameters of halo coronal mass ejections (CMEs). We consider 50 front-side full-halo CMEs (FFH CMEs), which are from the list of Michalek, Gopalswamy, and Yashiro (Solar Phys. 246, 399, 2007), whose asymmetric-cone model parameters and earthward-direction parameter were available. For each CME we use its projected velocity [V (p)], radial velocity [V (r)], angle between cone axis and sky plane [gamma] from the cone model, earthward-direction parameter [D], source longitude [L], and magnetic-field orientation [M] of its CME source region. We make a simple linear-regression analysis to find out the relationship between CME parameters and Dst index. The main results are as follows: i) The combined parameters [(V (r) D)(1/2) and V (r) gamma] have higher correlation coefficients [cc] with the Dst index than the other parameters [V (p) and V (r)]: cc=0.76 for (V (r) D)(1/2), cc=0.70 for V (r) gamma, cc=0.55 for V (r), and cc=0.17 for V (p). ii) Correlation coefficients between V (r) gamma and Dst index depend on L and M; cc=0.59 for 21 eastern events [E], cc=0.80 for 29 western events [W], cc=0.49 for 17 northward magnetic-field events [N], and cc=0.69 for 33 southward magnetic-field events [S]. iii) Super geomagnetic storms (Dsta parts per thousand currency signa%26apos;200 nT) only appear in the western and southward magnetic-field events. The mean absolute Dst values of geomagnetic storms (Dsta parts per thousand currency signa%26apos;50 nT) increase with an order of E+N, E+S, W+N, and W+S events; the mean absolute Dst value (169 nT) of W+S events is significantly larger than that (75 nT) of E+N events. Our results demonstrate that not only do the cone-model parameters together with the earthward-direction parameter improve the relationship between CME parameters and Dst index, but also the longitude and the magnetic-field orientation of a FFH CME source region play a significant role in predicting geomagnetic storms.
- 出版日期2014-6
