During SMM operation in 1980 the HXIS instrument detected a few giant coronal arches, extending to high altitude (-10 km) and with widely separated footpoints, which always appeared after tworibbon
(2-R) flares. The origin of these extensive structures is unknown, but their association with 2-R ovents suggests that both phenomena may be attributed to the same mechanism. Tlie continued energy release during the decay phase of 2-R flare is identifled with reconnection which allows an open field configuration to relax back to a lower energy state, lbe growing
post-flare loop system is the visible manifestation of this process, tracing the rise with time of the neutral point.
In this paper we examine the possibility that HXIS arches form as a result of magnetic rcconnection occurring at high levels. In order to test this hypothesis we develop a model capable of representing
the 3-dimensional geometry of a reconnecting magnetic field and compare model predictions with observations of the giant arch imaged by HXIS on May 22, 1980. We conclude tliat the topology
of the reconnected magnetic field, as well as the energy released by reconnection, are in good agreement with the observed shape and thermal energy content of tlie arch, supporting, at least in this
case, the hypothesis that HXIS arches form through the reconnection mechanism.