Katsukawa & Tsuneta (2001) found an excess fluctuation in soft X-rays coming from active regions, and proposed that the fluctuation was attributed to ubiquitous tiny bursts. They estimated the energy range of individual bursts to be 1020–1022 erg. There appears to be a big desert, the void in which no burst occurs for 3–6 orders of magnitudes in energy from the pico- flare range to the observed micro-flare range, indicating that a separate physical mechanism is responsible for the picoflares. We propose that the picoflares are due to Sweet-Parker reconnection, which is presumably easier to occur than the Petschek reconnection responsible for larger flares. We point out the critical importance of the simultaneous observations with Solar-B X-ray/EUV and visible-light telescopes.
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