Low geo-effectiveness of fast halo CMEs related to the 12 X-class flares in 2002

It is generally admitted that extreme space weather events tend to be related to strong flares and fast halo coronal mass ejections (CMEs). In the present paper, we systematically analyze the chains of events from the Sun to the Earth induced by all 12 X-class flares that occurred in 2002. It is very difficult to study the chain of events leading to geo-effectiveness when starting from the solar source, as opposed to starting from the CME or the ICME. In this admittedly small sample,we find an unusual high rate (58%) of solar sources with a longitude larger than 74 degrees. Yet, all 12 X-class flares are associated with at least one CME. The fast halo CMEs (50% ) are related to long duration flares, interplanetary CMEs (ICMEs) at L1 and weak Dst minimum valuea (>−51 nT); while 5 (41%) of the 12 X-class flares are related to solar proton events (SEP). We conclude that: (i) the min(Dst) and flare longitude are correlated, when related to an ICME at L1. Given the small sample, however, this might have happened only by chance. (ii) All twelve analysed solar events, even those associated with fast halo CMEs originating from the central disk region, and those inducing ICMEs and SEPs were not very geo-effective. This unexpected result demonstrates that the suggestive events in the chain (fast halo CME, X-class flares, central disk region, ICME, SEP) are not infallible proxies for geo-effectiveness. (iii) The low value of integrated and normalized southward component of the IMF (B∗z) may explain the low geo-effectiveness for this small sample. In fact, B∗z is well correlated to the weak Dst and low auroral electrojet (AE) activity. Hence, the only space weather impact at Earth in 2002 we can explain is based on B∗z at L1.

Publication year:2020

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CSS-citation score:1

Authors:International

Authors from:Higher Education

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