Relationship between the Magnetic Flux of Solar Eruptions and the Ap Index of Geomagnetic Storms

TL;DR

This study finds a significant correlation between the magnetic flux of solar eruptions and the Ap index of geomagnetic storms, indicating that larger solar eruptions tend to cause more intense geomagnetic activity, with potential for Ap values exceeding 400.

Contribution

It demonstrates a correlation between eruptive magnetic flux and the Ap index, extending understanding beyond the Dst index to include more severe geomagnetic storms.

Findings

Magnetic flux correlates with Ap index increases.

Ap index can exceed the traditionally maximum value of 400.

Larger solar eruptions lead to more intense geomagnetic storms.

Abstract

Solar coronal mass ejections (CMEs) are main drivers of the most powerful non-recurrent geomagnetic storms. In the extreme-ultraviolet range, CMEs are accompanied by bright post-eruption arcades and dark dimmings. The analysis of events of the Solar Cycle 23 (Chertok et al., 2013, Solar Phys. 282, 175) revealed that the summarized unsigned magnetic flux in the arcades and dimming regions at the photospheric level, $\Phi$, is significantly related to the intensity (Dst index) of geomagnetic storms. This provides the basis for the earliest diagnosis of geoefficiency of solar eruptions. In the present article, using the same data set, we find that a noticeable correlation exists also between the eruptive magnetic flux, $\Phi$, and another geomagnetic index, Ap. As the magnetic flux increases from tens to $\approx 500$ (in units of $10^{20}$ Mx), the geomagnetic storm intensity measured by the 3-hour Ap index, enhances in average from Ap $\approx 50$ to a formally maximum value of 400 (in units of 2 nT). The established relationship shows that in fact the real value of the Ap index is not limited and during the most severe magnetic storms may significantly exceed 400.