Estimation of Reconnection Flux Using Post-eruption Arcades and Its Relevance to Magnetic Clouds at 1 AU

Abstract

We report on a new method to compute the flare reconnection (RC) flux from post-eruption arcades (PEAs) and the underlying photospheric magnetic fields. In previous works, the RC flux has been computed using cumulative flare ribbon area. Here we obtain the RC flux as half of that underlying the PEA associated with the eruption using an image in EUV taken after the flare maximum. We apply this method to a set of 21 eruptions that originated near the solar disk center in Solar Cycle 23. We find that the RC flux from the arcade method (ΦrA) has excellent agreement with that from the flare-ribbon method (ΦrR) according to: ΦrA = 1.24(ΦrR) 0.99 . We also find ΦrA to be correlated with the poloidal flux (ΦP) of the associated magnetic cloud at 1 AU: ΦP = 1.20(ΦrA) 0.85 . This relation is nearly identical to that obtained by Qiu et al. (Astrophys. J. 659, 758, 2007) using a set of only nine eruptions. Our result supports the idea that flare reconnection results in the formation of the flux rope and PEA as a common process.

Coronal flux ropes and their interplanetary counterparts

“…It is possible to test this flux relationship using solar and interplanetary data since the ejected flux ropes at the Sun are detected in situ in the solar wind as magnetic clouds (MCs) (Burlaga et al 1981;Goldstein et al 1983;Klein and Burlaga, 1982). Qiu et al (2007) confirmed that the RC flux at the Sun is about the same as the poloidal flux of the corresponding MC at 1 au (see also Moestl et al 2009;Hu et al 2014;Gopalswamy et al 2017). Qiu et al (2007) determined the RC flux as the photospheric magnetic flux underlying the area swept up by the flare ribbons on one side of the polarity inversion line.…”

“…In order to do this, we compute the RC flux from source regions using the PEA technique recently developed by Gopalswamy et al (2017). According to this method, the RC flux is computed as half the unsigned photospheric magnetic flux underlying PEAs in the source region.…”

“…According to this method, the RC flux is computed as half the unsigned photospheric magnetic flux underlying PEAs in the source region. The RC flux has been taken to be the poloidal flux of the flux rope created during the eruption process as has been demonstrated theoretically (Longcope et al 2007) and observationally Hu et al 2014;Gopalswamy et al 2017). Equating the RC flux to the poloidal flux of the newly formed flux rope at the Sun, we determine the axial field in the coronal flux rope.…”

“…The fluence values were taken from the Solar Geophysical Data for most of the events; for some events (especially the ones associated with eruptive prominences) the fluence was not listed, so we computed it from the GOES soft X-ray flux. Φr was determined from the PEA method, which is half the sum of photospheric magnetic flux in each pixel in the area underlying the PEA (Gopalswamy et al 2017). Xie et al (2013) applied the EFR model to the white light images obtained by SOHO/LASCO using its C2 and C3 telescopes.…”

“…Qiu et al (2007) determined the RC flux as the photospheric magnetic flux underlying the area swept up by the flare ribbons on one side of the polarity inversion line. Gopalswamy et al (2017) introduced a new method of estimating the reconnected flux based on just PEAs, somewhat similar to the "flare flux" computed by Moore et al (2007). According to this arcade method, a single image in EUV or X-ray in the decay phase of the flare can be used to estimate the RC flux: half of the magnetic flux underlying the PEA is the RC flux.…”