Ground-based observations of thunderstorm-correlated fluxes of high-energy electrons, gamma rays, and neutrons

The Aragats Space Environmental Center facilities continuously measure fluxes of neutral and charged secondary cosmic ray incidents on the Earth’s surface. Since 2003 in the 1-minute time series we have detected more than 100 enhancements in the electron, gamma ray, and neutron fluxes correlated with thunderstorm activities. During the periods of the count rate enhancements, lasting tens of minutes, millions of additional particles were detected. Based on the largest particle event of September 19, 2009, we show that our measurements support the existence of long-lasting particle multiplication and acceleration mechanisms in the thunderstorm atmosphere. For the first time we present the energy spectra of electrons and gamma rays from the particle avalanches produced in the thunderstorm atmosphere, reaching the Earth’s surface.

Figure 1

The MAKET building at Aragats station, now hosting also ASNT, SEVAN, ArNM detectors, 3250 m above sea level.

Figure 2

Aragats Solar Neutron Telescope (ASNT).

Figure 3

Section of Aragats Neutron Monitor 18NM64 type; ArNM consists of 3 separate sections with 6 proportional chambers in each.

Figure 4

SEVAN detector measuring charged and neutral secondary cosmic rays.

Figure 5

One-minute time series detected by the MAKET array. (a) Count rate of the standalone outer detector. (b) Count rates of the “EAS triggers”—all 16 scintillators give signal within 400 nsecs. (c) The mean density of the particles generating the MAKET trigger conditions.

Figure 6

One-minute time series of the particle fluxes measured by ASNT. (a) 10 combination, signal only in top layer, mostly electrons with energy greater than 15 MeV. (b) 01 combination—mostly gamma rays with contamination of neutrons and electrons. (c) 11 combination—electrons and/or gamma rays with energy above 25 MeV. Additional particles are demonstrated by the dashed areas.

Figure 7

Unfolded electron and gamma ray spectra fitted by exponential and power functions.

Figure 8

One-minute time series of the particle flux detected by the SEVAN and ArNM detectors (a) 1-minute time series of ArNM. (b) 1-minute time series of SEVAN (010 combination). The additional particles are demonstrated by the dashed areas.

Figure 9

3-minute time series of ArNM on September 19, 2009.