  The emission of intense radio pulses by flaring magnetars is investigated.
Small-scale current gradients can be imprinted into a strongly magnetized
outflow by the same processes that source fireball radiation in the closed
magnetosphere. This structure arises from a combination of crustal yielding,
internal tearing, and turbulent cascade. We consider the quasi-linear
development of weak, small-scale currents as (i) they are stretched out and
frozen by relativistic expansion and then (ii) pass through a shock. In
particular, we derive the amplitudes of the ordinary and fast waves that emerge
downstream of a relativistically magnetized shock in response to a mode that is
frozen into the upstream flow (a frozen Alfv\'en wave or entropy wave). An
upstream mode with comoving wavelength exceeding the skin depth can linearly
convert to a secondary mode propagating above the plasma frequency. A simple
and accurate treatment of shocks with extreme magnetization is developed, and
the formation of internal shocks in the outflow from a bursting, rotating
magnetar is outlined. The emission process described here does not require a
strong shock or cool $e^\pm$ pairs (in contrast with the electromagnetic maser
shock instability). In some cases, a high-frequency wave is reflected back to
the observer, but with a minuscule amplitude that makes it subdominant to other
emission channels. The dominant secondary electromagnetic mode is superluminal
at emission, is subject to weak induced scattering within the outflow, and can
reach the observer in the radio band.
