Stopping muon effect and estimation of intracloud electric field

Abstract

Employing large thunderstorm ground enhancements (TGEs) as a manifestation of the strong electric field in thundercloud we measure fluxes of almost all species of secondary cosmic rays to estimate the strength of the intracloud electric field. The modulation that electric field poses on charged particle flux gives a sizable change in count rate of detectors measuring high energy muon flux and inclined muon flux in the presence of a TGE. The muon stopping effect, observed by the particle detectors located at 3200 m altitude at Aragats Space Environmental Center (ASEC) implicates the abrupt decline of count rate of high energy muons (at vertical incidence with energies above 250 MeV and at inclined incidence with azimuth angle θ> 22° for lower energies). For the large TGE events (relative enhancement > 10% in SEVAN detector upper layer, registering low energy charged particles and electrons) muon count rate decreases down to 2-5% from the mean count rate measured before the TGE event. A simple model of shifting of the energy spectrum of particles entering the electric field was applied for the analysis of several events where the muon stopping (deceleration) effect has been observed. For the large TGE events that occurred during last decade the maximal potential drop of 350 MV was estimated. The most probable electric field strength for this event was found to be ∼2 kV/cm.