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Using RHESSI and some auxiliary observations we examine possible connectionsbetween spatial and temporal morphology of the sources of non-thermal hardX-ray (HXR) emission which revealed minute quasi-periodic pulsations (QPPs)during the two-ribbon flares on 2003 May 29 and 2005 January 19. Microwaveemission also reveals the same quasi-periodicity. The sources of non-thermalHXR emission are situated mainly inside the footpoints of the flare arcadeloops observed by the TRACE and SOHO instruments. At least one of the sourcesmoves systematically both during the QPP-phase and after it in each flare thatallows to examine the sources velocities and the energy release rate via theprocess of magnetic reconnection. The sources move predominantly parallel tothe magnetic inversion line or the appropriate flare ribbon during theQPP-phase whereas the movement slightly changes to more perpendicular regimeafter the QPPs. Each QPP is emitted from its own position. It is also seen thatthe velocity and the energy release rate don't correlate well with the flux ofthe HXR emission calculated from the sources. The sources of microwaves andthermal HXRs are situated near the apex of the loop arcade and are notstationary either. Almost all QPPs and some spikes of HXR emission during thepost-QPP-phase reveal the soft-hard-soft spectral behavior indicating separateacts of electrons acceleration and injection, rather than modulation ofemission flux by some kinds of magnetohydrodynamic (MHD) oscillations ofcoronal loops. In all likelihood, the flare scenarios based on the successivelyfiring arcade loops are more preferable to interpret the observations, althoughwe can not conclude exactly what mechanism forces these loops to flare up.

Imaging Observations of Quasi-Periodic Pulsatory Non-Thermal Emission in Ribbon Solar Flares