Transcript Effect of the Electric Field of the Atmosphere on Cosmic Rays

Variations of Cosmic Rays during
Thunderstorms
N.S. Khaerdinov & A. S. Lidvansky
Institute for Nuclear Research, Russian Academy of Sciences,
Moscow, Russia
Motivation for these studies
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Secondary cosmic rays deep in the atmosphere represent a
continuous flux of charged particles whose propagation is disturbed
by many factors. During thunderstorms the strong electric field of
the atmosphere is one of such factors.
This electric field is highly variable in space and time and different
components of cosmic rays demonstrate a variety of response
effects.
Studying variations of cosmic rays during thunderstorms one can
hope to understand fundamental processes of atmosphere
dynamics.
Fields
Examples of vertical profiles of electric
field measured on balloons
(Marshall et al., 1996)
Particles
Model integral spectra of vertical flux of electrons, photons,
and muons at an altitude of 840 g/cm2 (1700 m a.s.l.).
 single electrons and positrons, conversion of old
experimental data.
■■■, □□□ model spectra of electrons and positrons, ●●●,
○○○ gamma-rays,  muons.
Examples of propagation of a runaway electron with initial
energy of 70 MeV in strong electric fields (3.2 and 4 kV per cm)
Cascades of particles generated by a single 1-MeV
electron in the electric field with a strength of 5 kV/cm
Baksan Air Shower Array (BASA)
Central Carpet
(400 liquid
scintillators)
Six huts
(108 liquid
scintillators)
Muon Detector
(175 plastic scintillators
under 2 m of rock).
Energy threshold 1 GeV
Location
Altitude of the
setup is 1700 m
above sea level.
In Baksan Valley
between
mountains whose
tops have altitudes
of 4000 m above
sea level.
Distances to these
peaks are about
5 km.
Mt. Andyrchi
EAS array
“Andyrchi”
“Carpet-2”
EAS array
Tunnel
entrance
Neutrino
village Neutrino
village
Universal instrument for measuring the near-ground
electrostatic field of the atmosphere and precipitation electric
current
Measurements of electrostatic
and slowly variable field in the
range from from -40 kV/m up
to +40 kV/m with an accuracy
of ~ 10 V/m.
Precipitation electric current is
measured in the range from -50
nA/m2 up to +50 nA/m2 with an
accuracy of ~ 10 pA/m2.
The instrument allows one to
measure not only thunderstorm
field but also the background
(fair weather) electric field by a
single method.
Amplitude spectrum from a layer of scintillators
Two thresholds are used to separate soft and hard components:
Soft component is detected by huts between low (Al) and upper (Ah)
thresholds. Electrons – 20%, positrons – 10%, -rays – 50%, admixture
of muons is less than 20%.
Hard component is measured by Carpet detectors (under concrete roof 29
g/cm2) above upper threshold (muons 90%)
Experimental data: soft component
I.
II.
Regular variations ‘intensity versus field’ averaged over
many thunderstorm events. Negative linear and positive
quadratic effects.
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)
Correlation the intensity of soft CR component with near-earth electric field as measured
and calculated (on the left panel). The difference (not explained by the spectrum
transformation in the field near the ground surface) is shown on the right panel
Accelerated near the ground
Electrons
Positrons
Accelerated in the clouds
Positrons
Electrons
Thunderstorm on July 31, 1999 (Marshall et al., 2005). Charge distribution.
Positive charge screens
the strong negative field
Thunderstorm on Sept 26, 2001,
Baksan Valley (North Caucasus)
Electric field
Soft component
(10-30 MeV)
Hard component
(> 100 MeV)
Intensity of muons
(> 1 GeV)
Experimental data: muons
I.
II.
Regular variations of muon intensity while
averaging over many thunderstorm periods.
Negative linear and negative quadratic effects,
strongly dependent on muon energy.
Strong variations (positive, negative, and bipolar)
with amplitudes up to 1% and typical duration of a
few minutes (maximum duration is 1.5 h).
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.
Muons with E > 100 MeV
Stopping muons
(15 < E < 90 MeV)
Muons with E > 1 GeV
Event on September 24,
2007. Purely muon effect.
Record enhancement
during thunderstorm on
October 11, 2003
Estimates of minimal
distance to two
lightning strokes exerting
strong effect on the
intensity are 4.4 and
3.1 km. Other lightning
discharges,including very
near, give no such an
effect.
The role of lightning
In the already shown
event of October 11,
2003 there are other
drops of intensity
correlating with lightning
strokes
Two lightning discharges of different polarities producing
a similar effect in the event on August 1, 2008
Event on September 11, 2005
(averaging 10 s)
In this event a lightning
discharge causes jumps
in the intensities of both
soft and hard components
Two examples of strong variations of muons during thunderstorms.
Events on September 24, 2000 and 2007. The latter demonstrates
sharp changes in muon intensity associated with lightning dischages.
Near-earth field
Soft component
(e, e+, ),
10-30 MeV
Hard component
(muons > 100 MeV)
Precipitation
electric current
Events on June 18, 2008 (left, averaged over 15 s) and
July 18, 2008 (right, averaged over 30 s)
Thunderstorm on
September 7-8, 2000
Averaging over 20 s
Thunderstorm on Sept 7, 2000, fine
structure of the large increase in the soft
component
Electric field
Soft component
(10-30 MeV)
Hard component
(> 100 MeV)
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
Event on 3 Sept, 2006. Parameter  is
the exponent of power law spectrum
approximating the data.
There are indications that this spectrum is
steeper than background spectrum
10-17 MeV
10 – 30 MeV
17-30 MeV
>30 MeV
Admissible regions for runaway and feedback particles
A model of particle generation in thunderclouds. Secondary CR are
seed particles and the electric field is a reservoir of energy
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):
 t  t0 
I ( SC , t )  I ( SC , t0 ) exp 
,
 TD 
TD 

K 2 ( D, x0, x1)
Monte Carlo calculations made by J. Dwyer (2003) considered feedback
processes too. However, this is another type of feedback and is essential only
for avalanches of runaway particles at enormous values of overvoltage.
Electric field strength is 1000 kV/m
Near the threshold (critical field)
characteristic length is close to
radiation length
Field strength versus field
extension for particle
generation process with
different rise time.
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.
Thunderstorms on October 15,
2007 (averaging of data over 20 s).
The event on October 15, 2007
Classification of geomagnetic pulsations
(amplitude from some tenth to tens of nT):
regular Pc and irregular Pi
Pc
Period, s
Pi
Period, s
Pc1
0,2 - 5
Pi 1 1 - 40
Pc 2 5 -10
Pi 2 40 - 150
Pc 3 10 - 45
Pi 3 > 150
Pc 4 45 - 150
Pc 5 150 - 600
Event on October 15, 2007.
From the plot of h–component the daily
trend is subtracted (below).
The best time resolution of 1 s (on the right).
Conclusions
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A model of a feedback cycling process is suggested for events
with exponential increase of intensity in secondary cosmic
rays of energy 10-30 MeV .
It is shown that the critical field and particle energy for this
process are 300 kV/m and 10 MeV, respectively.
These effects of particle generation should take place at high
altitudes and can be responsible for occurrence of anomalous
conductivity in the cloudy layer.
The rate of exponential growth of intensity depends on the
product DL, where D is the excess (in comparison to critical
value) strength of the field and L is its extension (complete
analogy with the Paschen’s law, where breakdown voltage
depends on the product of pressure and distance).