Estimation of Reconnection Flux using Post-eruption Arcades and Prediction of Bz at Earth

Coronal mass ejections (CMEs) and flares share the same eruption process as has been confirmed from various aspects of the two phenomena. In particular, the post-eruption arcade and the CME flux rope are formed out of the same reconnection process. It is customary to compute the flare reconnection flux from the flare-ribbon area and photospheric/chromosphericmagnetic field strength. Here we report on a new method to compute the reconnection flux from post-eruption arcades (PEAs). Instead of counting the ribbon pixels in a series of images, we simply measure the area under PEAs after the flare maximum and the underlying photospheric magnetic field. The reconnection flux is then half of the product of these two quantities. We illustrate this method using specific examples and show that the ribbon and arcade methods yield very similar results. We show that this method provides a simple means of predicting the 1-AU flux rope magnetic field (including Bz) from measurements made near the Sun.