Observations of quasi-harmonic amplification of solar flaring activity

  1. Space Research Institute (IKI) of Russian Academy of Sciences

An interesting and fairly rare event occurred in the NOAA active region 09393 on 2 April, 2001 - namely, a
series of 8 quasi-periodic solar X-ray flares of an increasing power up to X1.4. The characteristic time between
the peaks of the flares was 30 minutes. Unfortunately, there were no spatially-resolved X-ray observations of
the active region. Nevertheless, spatially-resolved observations of the active region made by the TRACE in
the extreme ultraviolet emission and also by the MDI magnetograph on board the SOHO satellite showed that
the flaring activity occurred in the penumbra of two sunspots of opposite polarity, connected by a system of
magnetic loops. The mechanism of quasi-periodic modulation of the observed flaring activity based on the MHD
oscillations of magnetic loops is discussed.