  We investigate the problem of scattering and conversion of monochromatic
planar gravitational and electromagnetic waves impinging upon a
Reissner-Nordstr\"om black hole using a Regge pole description, i.e., a complex
angular momentum approach. For this purpose, we first compute numerically the
Regge pole spectrum for various charge-to-mass ratio configurations. We then
derive an asymptotic expressions for the lowest Regge poles, and by considering
Bohr-Sommerfeld-type quantization conditions, obtain the spectrum of weakly
damped quasinormal frequencies from the Regge trajectories. Next, we construct
the scattering and conversion amplitudes as well as the total differential
cross sections for different processes using both a complex angular momentum
representation and a partial wave expansion method. Finally, we provide an
analytical approximation of the scattering and conversion cross sections of
different processes from asymptotic expressions for the lowest Regge poles and
the associated residues based on the correspondence Regge poles, "surface
waves" propagating close to the photon (graviton) sphere. This allows us to
extract the physical interpretation encoded in the partial wave expansions in
the high-frequency regime (i.e., in the short-wavelength regime), and to
describe semiclassically with very good agreement both black hole glory and a
large part of the orbiting oscillations, thus unifying these two phenomena from
a purely wave point of view.
