  Afterglows of gamma-ray bursts are observed to produce light curves with the
flux following power law evolution in time. However, recent observations reveal
bright flares at times on the order of minutes to days. One proposed
explanation for these flares is the interaction of a relativistic blast wave
with a circumburst density transition. In this paper, we model this type of
interaction computationally in one and two dimensions, using a relativistic
hydrodynamics code with adaptive mesh refinement called RAM, and analytically
in one dimension. We simulate a blast wave traveling in a stellar wind
environment that encounters a sudden change in density, followed by a
homogeneous medium, and compute the observed radiation using a synchrotron
model. We show that flares are not observable for an encounter with a sudden
density increase, such as a wind termination shock, nor for an encounter with a
sudden density decrease. Furthermore, by extending our analysis to two
dimensions, we are able to resolve the spreading, collimation, and edge effects
of the blast wave as it encounters the change in circumburst medium. In all
cases considered in this paper, we find that a flare will not be observed for
any of the density changes studied.
