  Solar flares are the most powerful explosions occurring in the solar system,
which may lead to disastrous space weather events and impact various aspects of
our Earth. So far, it is still a big challenge in modern astrophysics to
understand the origin of solar flares and predict their onset. Based on the
analysis of soft X-ray emission observed by the Geostationary Operational
Environmental Satellite (GOES), this work reported a new discovery of very
long-periodic pulsations occurred in the preflare phase before the onset of
solar flares (preflare-VLPs). These pulsations are typically with period of 8 -
30 min and last for about 1 - 2 hours. They are possibly generated from LRC
oscillations of plasma loops where electric current dominates the physical
process during magnetic energy accumulation in the source region. The
preflare-VLP provides an essential information for understanding the triggering
mechanism and origin of solar flares, and may help us to response to solar
explosions and the corresponding disastrous space weather events as a
convenient precursory indicator.
