Search for muon enhancement at sea level from transient solar activity
  This paper presents first results of an ongoing study of a possible association between muon enhancements at ground observed by the TUPI telescope and transient events such as the Sun's X-ray activity. The analysis of the observed phenomenon by using the GOES satellite archive data seems to indicate that on most cases the Ground Level Enhancements (GLEs) could potentially be associated with solar flares. We show that small scale solar flares, those with prompt X-ray emission classified as C class (power above $10^{-6}Watts m^{-2}$ at 1 AU) may give rise to GLEs, probably associated with solar protons and ions arriving to the Earth as a coherent particle pulse. The TUPI telescope's high performance with these energetic solar particles arises mainly from: (1) its high counting rate (up to $\sim 100$ KHz). This value in most cases is around 100 times higher than other detectors at ground and (2) due to its tracking system. The telescope is always looking near the direction of the IMF lines. The GLE's delay in relation of the X-ray prompt emission suggest that shock driven by corona mass ejection (CME) is an essential requirement for the particle acceleration efficiency. 
C.R.A. Augusto, C. E. Navia and M. b. Robba