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The cause of quasi-periodic pulsations (QPP) in solar flares remains thesubject of debate. Recently, Nakariakov & Zimovets (2011) proposed a new modelsuggesting that, in two-ribbon flares, such pulsations could be explained bypropagating slow waves. These waves may travel obliquely to the magnetic field,reflect in the chromosphere and constructively interfere at a spatiallyseparate site in the corona, leading to quasi-periodic reconnection eventsprogressing along the flaring arcade. Such a slow wave regime would havecertain observational characteristics. We search for evidence of thisphenomenon during a selection of two-ribbon flares observed by RHESSI, SOHO andTRACE; the flares of 2002 November 9, 2005 January 19 and 2005 August 22. Wewere not able to observe a clear correlation between hard X-ray footpointseparations and pulse timings during these events. Also, the motion of hardX-ray footpoints is shown to be continuous within the observational error,whereas a discontinuous motion might be anticipated in the slow wave model.Finally, we find that for a preferential slow wave propagation angle of 25-28degrees that is expected for the fastest waves, the velocities of the hardX-ray footpoints lead to estimated pulse periods and ribbon lengthssignificantly larger than the measured values. Hence, for the three eventsstudied, we conclude that the observational characteristics cannot be easilyexplained via the Nakariakov & Zimovets (2011) propagating slow wave model whenonly angles of 25-28 degrees are considered. We provide suggested flareparameters to optimise future studies of this kind.

The relationship between hard X-ray pulse timings and the locations of footpoint sources during solar flares