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

Abstract

It is generally accepted that extreme space weather events tend to be related to strong flares and fast halo coronal mass ejections CMEs. In the present paper, we carefully identify the chain of events from the Sun to the Earth induced by all 12 X-class flares that occurred in 2002. In this 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 interplanetary CMEs (ICMEs) at L1 and weak Dst minimum values ($>-51$nT); while 5 (41\%) of the 12 X-class flares are related to solar proton events (SPE). We conclude that: (i) All twelve analyzed solar events, even those associated with fast halo CMEs originating from the central disk region, and those ICMEs and SPEs were not very geo-effective. This unexpected result demonstrates that the suggested events in the chain (fast halo CME, X-class flares, central disk region, ICME, SPE) are not infallible proxies for geo-effectiveness. (ii) The low value of integrated and normalized southward component of the IMF ($B_z^{\ast }$) may explain the low geo-effectiveness for this small sample. In fact, $B_z^{\ast }$ 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 $B_z^{\ast }$ at L1.

33 pages, 12 figures

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