Solar flares are the most energetic phenomenon in the solar system, and have been
recognized as a prototype of cosmic flares and explosions. The central engine is now
believed to be magnetic reconnection. Because magnetic reconnection is a highly
dynamical process, it is expected that many magnetohydrodynamic (MHD) waves and shock
waves will be generated during flares in some way. MHD waves can tell us the
quantitative information of the plasma conditions, and shocks could be important for
generating high-energy particles. For these reasons, it has been extensively studied
their origin. 

Recent observations discovered MHD waves emitted from flaring regions. Furthermore,
observations pointed out that emission of MHD waves from the flaring sites and
non-thermal emissions from high-energy particles looks correlated. However, because of
the complexity of the flaring regions, the generation mechanism of MHD waves and causal
relation to the non-thermal emissions have not been understood yet. 

To reveal the dynamical processes related to the wave/shock generation, we performed 2D
MHD simulations of a solar flare. As a result, we discovered the local oscillation of
the flare loop-top and the generation of quasi-periodic MHD waves from such oscillating
flare loop-top. The new model unveiled that the loop-top is full of shocks and waves. If
the particle acceleration is actually related to the shocks, for the first time we
revealed the origin of MHD waves and causal relation between MHD waves and particle
acceleration. Furthermore, we point out that this study may help us to derive physical
quantities of flares from the oscillation seen in flare light curves. This will be
important for estimating physical quantities of stellar flares whose structure cannot be
resolved. In this talk, I will show our recent results, and discuss the application of
this study.