N.S. Khaerdinov & A. S. Lidvansky Dynamics of Cosmic Rays in Thunderstorm Atmosphere and Generation of Elementary Particles by Thunderclouds N.S. Khaerdinov & A. S. Lidvansky  Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia

Plan Experimental data obtained at Baksan on variation of the CR soft component (10-30 MeV) and muons during thunderstorms Calculated transformation of energy spectra of the soft component in weak near-earth electric field. Can describe regular behavior of CR intensity at moderate fields Calculated transformation of energy spectra in strong (critical) field of clouds. Cannot describe the bright enhancements of intensity with sections of exponential growth The model of particle production in thunderclouds is suggested based on a feedback cycling process

Experimental data: soft component Regular variations ‘intensity versus field’ averaged over many thunderstorm events. Strong enhancements of intensity (often before lightning) that sometimes demonstrate exponential increase Published in N.S. Khaerdinov, A.S. Lidvansky, and V.B. Petkov, Electric Field of Thunderclouds and Cosmic Rays: Evidence for Acceleration of Particles (Runaway Electrons), Atmospheric Research, vol. 76, issues 1-4, July-August 2005, pp. 346-354.

Relative deviation of the soft component intensity from the mean value versus local field (52 thunderstorm events)

Thunderstorm on Sept 26, 2001, Baksan Valley (North Caucasus) Electric field Soft component (10-30 MeV) Hard component (> 90 MeV) Intensity of muons (> 1 GeV)

Experimental data: muons Regular variations ‘intensity versus field’ averaged over many thunderstorm events. Negative linear and negative quadratic effect Strong dependence on the muon threshold energy (both linear and quadratic coefficients increase with decreasing threshold) N.S. Khaerdinov, A.S. Lidvansky, and V.B. Petkov, Variations of the Intensity of Cosmic Ray Muons due to Thunderstorm Electric Fields, 29th Intern. Conf. on Cosmic Rays, Pune, August 3-10, 2005, vol. 2, pp. 389-392.

Electric field strength Soft component Muons >1 GeV Hard component Thunderstorm on August 6, 2003, averaging over 15 s, one of the longest and most profound muon effect Electric field strength Soft component Muons >1 GeV Hard component (muons > 90 MeV) Stopping muons (20-80 MeV)

Muons with E > 90 MeV Stopping muons (20 < E < 80 MeV) Muons with E > 1 GeV

Weighted mean coefficients of approximations by second-degree polynomials of the intensity – field regression curves for different components Component Energy Linear coefficient, % per kV/m Quadratic coefficient, % per (kV/m)2 Muons > 1 GeV  0.00277  0.00034  0.00045  0.00005 Hard component (muons) > 90 MeV  0.00794  0.0013  0.00235  0.00002 Stopping muons 20 – 80 MeV  0.04124  0.01260  0.00845  0.00201

A great increase of the soft component The event of September 7, 2000 A view on a large time scale Averaging over 4-s intervals

Electric field Soft component (10-30 МэВ) Hard component (> 70 МэВ) Thunderstorm on Sept 7, 2000, fine structure of the largest increase in the soft component Electric field Soft component (10-30 МэВ) Hard component (> 70 МэВ) Precipitation electric current

Sept 7, 2000 event The largest increase is exponential with high precision and has an abrupt stop at the instant of lightning

Outstanding event during thunderstorm on Oct 11, 2003 The largest enhancement ever detected Lightning strokes interrupt the fast exponential rise in one case and slow exponential decay in the other

Accelerated near the ground Accelerated in the clouds Correlation of the intensity of soft CR component with near-earth electric field as measured and calculated (on the left panel). The difference (effect not explained by the spectrum transformation in the weak field near the ground surface is shown on the right panel. Accelerated near the ground Accelerated in the clouds Electrons Positrons Positrons Electrons

Examples of vertical profiles of thunderstorm electric field measured in a balloon experiment (Marshall et al., 1996)

Due to this structure, there is always a field with an opposite sign The layered structure of electric field in the atmosphere during thunderstorms (measured and used in calculations). S.S. Davydenko et al., 12 Int. Conf. on Atmospheric Electricity, Versailles, 2003) Due to this structure, there is always a field with an opposite sign overhead

Admissible regions for runaway and feedback particles

Under stable conditions and at sufficient strength (D) and extension (from x0 to x1) of the field the intensity of particles increases exponentially (K is the probability of one cycle, and  is its duration):

Different effect of lightning in the Oct 11, 2003 event The estimates of minimum distances are 4.4 and 3.1 km for the two lightning having strong effect. No effect is produced by the third nearby lightning.

Field strength versus field extension for particle generation process with different rise time. Red line is the boundary of stability, thick blue line corresponds to 10 s, as e-folding time in our 11 Oct 2003 event. Fundamental limit on electrostatic field in air calculated by J.R. Dwyer. Monte Carlo simulation (Geophys. Res. Lett., 30, 2055 (2003)) at a pressure of 1 atm.

The upper limits to which intensity can be increased due to transformation of equilibrium background electron-positron spectrum of cosmic rays by strong (critical) electric field versus the lower boundary of this field (analysis of Oct 11, 2003 event) Analytical estimates (solid lines) made under extreme assumptions and the results of Monte Carlo simulations (points) for gamma-rays starting from three altitudes (1, 2, and 3 km) with an ultimately steep energy spectrum. Vertical line corresponds to the altitude of near mountains (~ 4000 m a.s.l.).

Arguments in favor of the suggested mechanism Intervals with exponential growth of intensity are explained in a natural way Distances to lightning discharges having an effect on the development of the process agree with sufficiently distant location of acceleration region (intensity argument) The spectrum of the observed effect is far steeper than extreme estimation for spectrum transformation effect (spectral argument) But more direct proof is needed!

Conclusions At moderate field strengths the transformation of the spectrum of cosmic rays is measured. There are enhancements of the soft component of cosmic rays that do not correlate with measured near-earth field. We interpret them as Wilson’s runaway electrons (or -rays from them). Events with fast exponential increase of intensity are interpreted as a feedback effect for runaway particles. It is shown that the critical field and particle energy for this process are 300 kV/m and 10 MeV, respectively.

The view on the feedback process applications (more conclusions): From the point of view of… Generation of particles by thunderclouds is: Environment science New type of natural radioactivity Climatology Amplification factor for CR effects Physics of atmosphere Mechanism of regulation of electric field strength and ion production Physics of gas discharge New type of discharge stimulated by relativistic particles Physics of particle acceleration Effect of bulk acceleration of diffused particle flux in dense medium Astrophysics Ready model of gamma-ray sources (including cosmic gamma-ray bursts)