Abstract
The geoeffectiveness of some coupling functions for the Solar Wind-Magnetosphere Interaction had been studied. 58 storms with peak Dst < −100 nT were used. The result showed that the interplanetary magnetic field Bz appeared to be more relevant with the magnetic field B (which agreed with previous results). However, both the V (solar wind flow speed) and Bz factors in the interplanetary dawn-dusk electric field (V×Bz) are effective in the generation of very intense storms (peak Dst < −250 nT) while “intense” storms (−250 nT ≤ peak Dst < −100 nT) are mostly enhanced by the Bz factor alone (in most cases). The southward Bz duration BT seems to be more relevant for Dst < −250 nT class of storms and invariably determines the recovery phase duration. Most of the storms were observed to occur at midnight hours (i.e., 2100–0400 UT), having a 41.2% incidence rate, with high frequency between 2300 UT and 0000 UT. 62% of the events were generated as a result of Magnetic Cloud (MC), while 38% were generated by complex ejecta. The B-Bz relation for the magnetic cloud attained a correlation coefficient of 0.8922, while it is 0.7608 for the latter. Conclusively, Bz appears to be the most geoeffective factor, and geoeffectiveness should be a factor that depends on methods of event identification and classification as well as the direction of event correlation.
Highlights
Magnetic storm occurs at periods during which the global magnetic field, as measured by low-latitude ground magnetometers, significantly decreases
The summary of the results was highlighted in Table 6. 62% of the events were as a result of magnetic cloud (MC), while 38% were generated by complex ejecta
Previous works have shown that the southward interplanetary magnetic field Bz is the most geoeffective factor in the solar wind-magnetosphere coupling function
Summary
Magnetic storm occurs at periods during which the global magnetic field, as measured by low-latitude ground magnetometers, significantly decreases. Gonzalez and Tsurutani [2] define a southward IMF of at least −10 nT for more than 3 hours as a sufficient condition for the development of an intense magnetic storm. They further associate these long-duration and intense IEF enhancements either with high-speed streams or with solar wind density enhancement events, presumably known as coronal mass ejections (CMEs). These are large plasma clouds ejected from the Sun and which are characterized by intense flux-rope-like magnetic fields and low dynamic pressures. Gosling et al [3] had suggested that CMEs, those associated with a shock, are regarded as the most important drivers of strong global geomagnetic activity
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