Magnetic Flux of EUV Arcades and Dimmings as a Relevant Parameter

for Early Diagnostics of Solar Eruptions Sources of Non-Recurrent

Geomagnetic  Storms and Forbush Decreases

 

I.M. Chertok (1), V.V. Grechnev (2), A.V. Belov (1), A.A. Abunin (1)

(1) Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Troitsk, Moscow, Russia
(2)  Institute of Solar-Terrestrial Physics SB RAS, Irkutsk, Russia


Abstract.  This study is aimed at the early diagnostics of the coronal mass ejection (CME) geoeffectiveness from quantitative parameters of accompanying EUV dimmings and arcades. We study events of the 23th cycle, in which major non-recurrent geomagnetic storms (GMS) with Dst < -100 nT are sufficiently reliably identified with their solar sources in the central part of the disk. Using the SOHO EIT 195 images and MDI magnetograms, we select significant dimming and arcade areas and calculate summarized unsigned magnetic fluxes in these regions at the photospheric level. The high relevance of this eruption parameter is displayed by its pronounced correlation with the Forbush decrease (FD) magnitude, which, unlike GMSs, does not depend on the sign of the Bz component, being determined by global characteristics of ICMEs. Correlations with the same magnetic flux in the solar source region are found for the GMS intensity (at the first step, without taking into account factors determining the Bz component near the Earth), as well as for the temporal intervals between the solar eruptions and the GMS onset and peak times. The larger magnetic flux, the stronger FD and GMS intensities and the shorter ICME transit time are. The revealed correlations indicate that the main quantitative characteristics of major non-recurrent space weather disturbances are largely determined by measurable parameters of solar eruptions, in particular, by the magnetic flux in dimmings and arcades, and can be tentatively estimated in advance with a lead time from 1 to 4 days. For GMS intensity, the revealed dependencies allow one to estimate a possible value, which can be expected if the Bz component is negative.


Figure 1: Dimmings and arcades in sources of the strongest GMSs of the 23rd cycle  

 

Table: parameters of GMSs, FDs and their solar eruptive sources  

 

Figure 2: An illustration of extraction of the dimming and arcade areas and calculation of their magnetic flux  

 

Figure 3: FD magnitude vs. eruptive magnetic flux  

 

Figure 4: Geomagnetic storm intensiry (Dst index) vs. eruptive magnetic flux  

Figure 5: Geomagnetic storm onset and peak transit times vs. eruptive magnetic flux  


 PDF file  of the paper accepted to Solar Phys. (2012),  DOI: 10.1007/S11207-012-0127-1; see preprints 1 and 2

 



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