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Multi-Wavelength Investigations of Solar Activity c 2004 International Astronomical Union Proceedings IAU Symposium No. 223, 2004 A.V. Stepanov, E.E. Benevolenskaya & A.G. Kosovichev, eds. DOI: 00.0000/X000000000000000X

Review of exp erimental results on geo effectiveness of solar and interplanetary events
Yu.I. Yermolaev and M.Yu. Yermolaev
Space Research Institute (IKI), Profsoyuznaya 84/32, Moscow 117997, Russia email: yermol@iki.rssi.ru Abstract. We present a brief review of published results on the geomagnetic storm effectiveness of CMEs and solar flares as well as of interplanetary events. Attention is drawn to the fact that the published values of storm effectiveness are in conflict with one another. Possible reasons of their differences are discussed. Keywords. Sun: coronal mass ejections and flares, Solar wind, Geomagnetic storms

1. Intro duction
At the present time the quantity of publications on solar event ­ geomagnetic storm connections has steadily grown. However, attention is drawn to the fact that these publications contain strongly diverging estimations of geoeffectiveness of those or other solar phenomena. For example, estimations of CME geoeffectiveness change from 35-45% up to 83-100% (see, for instance paper by Yermolaev & Yermolaev (2003b) and references therein). The aim of our paper is to compare different methods of solar-terrestrial physics and to explain exiting discrepancies in published results.

2. Results and conclusions
We made a review of published results and found that different results arise due to differences in the methods used to analyze the data: (1) the direction in which the events are compared, (2) the pair of compared events, and (3) the methods of the event classifications (see preliminary version of study by Yermolaev & Yermolaev (2003b) ). We selected papers (see Fig.1) using (1) the analysis on direct and back tracing of events, and (2) solar (coronal flares and CMEs), interplanetary (magnetic clouds and ejecta) and geomagnetic disturbances (storms on Dst and Kp indices). The classifications of magnetic storms by the Kp and Dst indices, the solar flare classifications by optical and X-ray observations, and the classifications of different geoeffective interplanetary events are compared and discussed by Yermolaev and Yermolaev (2003b). Taking into account this selection, all published results on the geoeffectiveness agree to each other in each subset: C M E S torms ­ 35-50%, C M E M C, E j ecta ­ 60-80%, M C, E j ecta S torm ­ 50-80%, S torm M C, E j ecta - 30-70%, M C, E j ecta C M E - 50-80%, S torm C M E ­ 80-100%, F lare S torms ­ 30-40% and S torms F lare - 50-80%. Higher values of correlations were obtained by back tracing, that is, by method, in which they were defined as the probability of finding candidates for a source of geomagnetic storms among CMEs and flares, and, strictly speaking, these values are not true estimates 1


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Figure 1. Schematic view of correlations between CME, MC/ejecta and magnetic storms for direct (top panel) and back (bottom panel) tracings. Relations of probabilities for 1­ and 2­step tracings are shown below each panels

of the geoeffectiveness. The latter results are also in contrast with the results of the twostage tracing of the events: first a storm - an interplanetary disturbance, and then an interplanetary disturbance - a CME/flare (see Fig.1). Estimations of CME (35-50%) and solar flare (30-40%) geoeffectiveness are close to each other and can be partially a result of random processes (Yermolaev and Yermolaev (2003a)) and, therefore, the forecast of geomagnetic conditions on the basis of observations of the solar phenomena can contain high level of false alarm. To increase reliability of the forecast, the further analysis of the solar data and revealing of characteristics which would allow us to select the phenomena among CMEs and/or flares with higher geoeffectiveness are required. Acknowledgements Paper is supported in part by Physical Department of Russian Academy of Sciences, Program N 18, and RFBR, grant 04-02-16131-a. References
Yermolaev, Yu. I., Yermolaev, M. Yu. 2003a Cosmic Research 41, 105­109. Yermolaev, Yu. I., Yermolaev, M. Yu. 2003b Cosmic Research 41, 539­549.