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.

Current views on impulsive and gradual solar energetic particle events

“…These particles are believed to be trapped below the CME (Reames 2002). Long-duration flares result from either continuous reconnection below the core of the CME or free-falling plasma, visible as down-flows in soft x-ray images (Shibasaki 2002).…”

Astrophysics in 2002

“…The associated microwave emission was identified to be nonthermal, probably caused by an apparent motion driven by successive injections of high-energy electrons into preexisting, higher elongated loops (Nakajima & Yokoyama 2002;Kim et al 2001). Because some of the ejected matter falls back to the surface, Shibasaki (2002) proposed that a part of the potential energy of the falling matter can be converted into thermal energy and heat itself up to temperatures of several million Kelvins, and this way can provide energy and mass supply for long duration flares, rather than by magnetic reconnection.…”

Investigation of long-duration arcade flares

“…Detailed analysis of satellite observations carried out by many authors has led to several important results (e.g. Sheeley et al 1975;Kahler et al 1977;Feldman et al 1995;Harra-Murnion et al 1998;Shibasaki 2002). One of the most important conclusions is that continuous energy release and plasma heating must exist during the LDAF decay phase to ensure the long duration of their loop-top kernels in spite of radiative and conductive losses (Vorpahl et al 1977).…”