On two distinct shocks during the flare of 9 July 1996

Due to the emission of shock-accelerated electrons, broadband radio observa tions display propagating super Alfvenic shock waves in the low corona ('ty pe II bursts'). We study the 9 July 1996 flare (AR NOAA 7978) focusing on t he aspect of shock generation. This event's radio spectrogram shows two dif ferent type II bursts in sequence. Radio imaging data (Paris, Meudon Observ atory) reveal that both bursts appear at different sites above the H alpha flare. The driver of the first type II burst seems to propagate with twice the speed of the second one. The projected source site of the first type II burst (seen earlier and at higher frequencies) is spatially situated furth er away from the H alpha flare site than the source of the second type II b urst. We try to understand this by comparing with Yohkoh soft X-ray images. The first shock source occurs near the top of high soft X-ray loop structu res. Its driver can be a guided fast mode magnetic disturbance. The second type II source appears in-between two high soft X-ray loop systems. This mi ght be a piston-driven disturbance powered by an evaporation front. We get a consistent picture only by assuming a very inhomogeneous Alfven speed in the active region's atmosphere.