  In this paper we study the lateral instability of streamer discharges using a
continuum discharge model. We observe similarities to Kelvin-Helmholz
instability in fluids. In strong electric fields, lateral long wave length
perturbations can grow while small wave length perturbations diminish during
the discharge evolution. We perform numerical simulations and carry out
asymptotic analysis of the instability. Our results could explain the growth
observed in experimental discharges.
