  We study physical mechanisms that trigger transient growth in a high-speed
spatially-developing laminar boundary layer that interacts with an oblique
shock wave. We utilize an approach based on power-iteration, with the global
forward and adjoint linearized equations, to quantify the transient growth in
compressible boundary layers with flow separation. For a Mach 5.92 boundary
layer with no oblique shock wave, we show that the dominant transient response
consists of oblique waves, which arise from the inviscid Orr mechanism, the
lift-up effect, and the first-mode instability. We also demonstrate that the
presence of the oblique shock wave significantly increases transient growth
over short time intervals through a mechanism that is not related to a slowly
growing global instability. The resulting response takes the form of spanwise
periodic streamwise elongated streaks and our analysis of the linearized
inviscid transport equations shows that base flow deceleration near the
reattachment location contributes to their amplification. The large transient
growth of streamwise streaks demonstrates the importance of non-modal effects
in the amplification of flow perturbations and identifies a route for the
emergence of similar spatial structures in transitional hypersonic flows with
shock wave/boundary-layers interaction.
