Magnetohydrostatic model of a bald-patch flare

On 18 May, 1994, a subflare was observed in AR 7722 in X-rays by Yohkoh/SXT and in H alpha at National Astronomical Observatory of Japan. The associat ed brightenings are due to small-scale magnetic energy release, triggered b y parasitic fluxes emerging and moving at the edge of leading sunspots. Usi ng the magnetohydrostatic equations derived by Low (1992), we model the mag netic field configuration by extrapolation of the Kitt Peak photospheric fi eld, taking into account the effects of pressure and gravity. H alpha flare kernels are shown to be located at computed separatrices associated with f ield lines which are tangent to the photosphere, namely 'bald patches' (BPs ). This is evidence that BPs can be involved in flares, and that current sh eets can be dissipated in low levels of the solar atmosphere. The presence of dense plasma which is supported against gravity in the magnetic dips abo ve BPs is correlated to dark elongated features observed in H alpha. Mass f lows in these flat fibrils are discussed in the context of energy release i n the BP separatrices. The effect of the plasma on the computed magnetic co nfiguration is shown to be of secondary importance with respect to the topo logy of the field.