An experimental investigation was performed of the discharge structure in a nonequilibrium plasma flowing at supersonic velocities through a linear, magnetohydrodynamic channel. Optical observations showed that the luminosity of the discharge was concentrated in streamers. The streamers were transverse to the gas velocity, they originated in the entrance region of the channel, and they propagated downstream at the local gas velocity. In addition, in the channel entrance region, where the axial electron density gradient and the convective effect were at a maximum, high-luminosity gas layers were observed on the electrode walls. These observations suggested that the discharge structure is determined by the following sequence of events occurring at the electrodes in the channel entrance region: electrical ignition of the gas, convective extinguishing, and subsequent reignition. Although streamer formation is also predicted by the theory of ionization instabilities in magnetoplasmas, other characteristics of the discharge were in disagreement with the theory. A major difference was the absence in the present experiments of plasma turbulence at large Hall parameters.