Energy and Mass Supply in the Decay Phase of Long-Duration Solar Flare Events

Abstract

A new mechanism is proposed to supply energy and mass in the decay phase of long-duration solar flare events. The long-duration event (LDE) flares are known to be caused by filament eruptions, and bright arcade structures continue for several hours or even a day. To overcome the short cooling time, continuous energy and mass supplies are required. Continuous magnetic reconnection in the current sheet extended above the arcade has been proposed to supply energy and mass. However, no direct observations of the current sheet have been reported. The new mechanism that we are proposing is based on the recent observations of downflows onto the top of arcades along the vertical spiky features observed by the Yohkoh soft X-ray telescope. We interpret these downflows as free-falling plasma. Plasma falling from a high altitude can convert its potential energy into thermal energy and heat itself with an average temperature of several million kelvins. Observations show that the downflows continue for several hours. Coronagraph observations by the Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph also show many falling features after coronal mass ejections. Instead of magnetic reconnection, we propose that these falling plasmas are the source of the energy and mass supply for LDEs in the long-lasting decay phase.