Nonthermal velocity evolution in the precursor phase of a solar flare

We present observations of two solar flares occurring in Active Region 7590 on 1993 October 3 using data from the Yohkoh spacecraft. The hard X-ray bu rsts from the two flares occurred within an 18 minute interval, with the so ft X-ray emission having a shorter separation of approximate to5 minutes. B oth flares occurred within one Yohkoh orbit, and hence we have continuous c overage of the soft X-ray line broadening at the peak of the first flare, r educing to the active region level of 33.5 km s(-1) in S xv (66.1 km s(-1) in Ca XIX) and then increasing to the peak in the second flare. The rise ab ove the active region background level begins 11 minutes before the start o f the second flare as defined by the start of the hard X-ray emission. Duri ng this extended rise time of V-nt,, there is no increase in the light curv es or the electron temperature. We suggest that this increase is an indicat or of turbulent changes in the active region prior to the flare that are re lated to the flare trigger mechanism.