Investigation of long-duration arcade flares

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Aims. We analyse three well-observed long-duration arcade flares (LDAFs) to find their general properties. Results concerning energy release in LDAFs (energy balance and diagnostic diagrams) are shown. Methods. Yohkoh observations and Kitt Peak Vacuum Telescope magnetograms are used to determine physical parameters of flare loop-top kernels (temperature, density, altitude). Using these parameters the energy release is studied in detail. Results. We found that: (1) the energy release in LDAFs occurs during their whole decay phase; (2) the kernel heating ( E H ) is of the order of 0.01–1 erg cm -3 s -1 ; (3) the kernels usually cannot be distinguished in SXT images when E H is drops below a particular value. This value depends on the altitude of the kernels.