  Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs)
descending from reconnection regions toward solar post-flare arcades seem to be
two different observational signatures of retracting, isolated reconnected flux
tubes with irreducible three-dimensional geometries. This dissertation
describes work in refining and improving a novel model of patchy reconnection,
where only a small bundle of field lines is reconnected across a current sheet
and forms a reconnected thin flux tube. Traditional models have not been able
to explain why some of the observed SADs appear to be hot and relatively devoid
of plasma. The present work shows that plasma depletion naturally occurs in
flux tubes that are reconnected across nonuniform current sheets and slide
trough regions of decreasing magnetic field magnitude. Moreover, through a
detailed theoretical analysis of generalized thin flux tube equations, we show
that the addition to the model of pressure-driven parallel dynamics, as well as
temperature-dependent, anisotropic viscosity and thermal conductivity is
essential for self-consistently producing gas-dynamic shocks inside reconnected
tubes that heat and compress plasma to observed temperatures and densities. The
shock thickness can be as long as the entire tube and heat can be conducted
along tube's legs, possibly driving chromospheric evaporation. We developed a
computer program that solves numerically the thin flux tube equations that
govern the retraction of reconnected tubes. Simulations carried out with this
program corroborate our theoretical predictions. A comparison of these
simulations with fully three-dimensional magnetohydrodynamic simulations is
presented to assess the validity of the thin flux tube model. We also present
an observational method based on total emission measure and mean temperature to
determine where in the current sheet a tube was reconnected.
