Thundercloud electrodynamics and its influence on high-energy

radiation enhancements and lightning initiation

E.A. Mareev1, D.I. Iudin1, V.A. Rakov1,2, A.Yu. Kostinskiy1,3, V.S. Syssoev1,4

1Institute of Applied Physics RAS, Nizhny Novgorod, Russia2Department of Electrical and Computer Engineering, University of Florida, USA

3National Research University Higher School of Economics, Moscow, Russia4High-Voltage Research Center of the Institute of Electrical Engineering, Istra,

Moscow region, Russia

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Outline

Experimental data on the multi-layer charge structure of thunderstorm clouds.

The lower positive charge region (LPCR) and its possible effects on the development of CG and IC discharges and thunderstorm ground enhancements.

Fractal simulation code enabling to examine the occurrence of lightning flashes of different type as a function of the cloud charge structure.

Recent observations of electrical discharges in the artificial cloud of charged water droplets,

Description of a complex hierarchical network of interacting channels at different stages of development.

Some perspectives

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Sources of the secondary cosmic rays detected on the Earth's surface (Chilingarian, JASTP, 2014)

Cloud electrical environment

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A vertical tripole representing the idealized gross charge structure of a thundercloud such as that shown in the left panel; the negative screening layer charges at the cloud top is ignored here.

An isolated thundercloud in central New Mexico, with a rudimentary indication of how electric charge is thought to be distributed inside and around the thundercloud, as inferred from the remote and in situ observations. Adapted from Krehbiel (1986).

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Current description; ordinary clouds and MCS

S. Davydenko, E.Mareev,

T.Marshall, M.Stolzenburg, JGR, D5, 2004

Shepherd R.T., W.D. Rust, and T. C.

Marshall , Electric fields and charges near

0 C in stratiform clouds, Monthly

Weather Review, V.124, May 1996.

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Conceptual model of the electrical structure in mature, mid-latitude convection. Fourmain charge regions (with red + for positive charge, blue – for negative charge) are typically

found in soundings through updrafts, while soundings outside updrafts have at least six charge regions in common. Representative electric field (E) and electrostatic potential (V) profiles in the nonupdraft (left) and updraft (right) of the convective region are also shown;

the altitudes in these soundings do not correspond exactly to the conceptual model. Schematic representations of an intracloud flash (in green) and a cloud-to-ground flash (in purple) are shown as they might appear in lightning mapping data (Stolzenburg and Marshall, 2009)

Thunderstorm 1-2 June, 2015

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Electric field variations: thunderstorm of July 17, 2005

Klimenko et al., 2007

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Electric field variations: thunderstorm of July 18, 2006

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Transfer of electrical space charge from corona between ground and thundercloud: Measurements and modeling (Chauzy et al., JGR,1991; Soula, JGR, 1994)

We interpret the preliminary breakdown (PB) pulse train as being generated when a negatively-charged channel extends downward from the main negative charge region and encounters an appreciable lower positive charge region (LPCR). When the LPCR is small no PB pulse train may be produced.

While the LPCR may serve to enhance the electric field at the bottom of the negative charge region and thereby facilitate the launching of a negatively-charged leader toward ground, presence of excessive LPCR may prevent the occurrence of negative CG flashes by ‘‘blocking’’ the progression of descending negative leader from reaching ground.

We infer four conceptual lightning scenarios that may arise depending upon the magnitude of the LPCR.

A. Nag and V.A. Rakov, Geophys. Res. Lett., doi:10.1029/2008GL036783, 2009 A. Nag and V.A. Rakov, Geophys. Res. Lett., doi:10.1029/2008GL036783, 2009

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Role of Lower Positive Charge Region in facilitating Different Types of Lightning

Left panel is a schematic illustration (not to scale) of electric field enhancement and reduction effects of the lower positive charge region (+QLP) below the main negative charge

region (-QN). The main positive charge region is not shown. Arrows indicate the direction of

vertical components of electric field vectors. The total electric field is enhanced, (EN + ELP),

between the negative and positive charge regions and reduced, (EN – ELP), below the

positive charge region.Right panel shows (a) schematic representation of preliminary breakdown stepping process in negative ground flashes. Negatively-sloped arrow indicates the overall downward extension of negatively charged channel through the LPCR. Three steps giving rise to current (and light) pulses are shown. Each current pulse originates at the tip of downward-extending channel and propagates upward (positively-sloped arrows). (b) A sketch of expected electric field record of resultant wideband PB pulse train.

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The left panels, A-D, schematically show four types of lightning that may arise depending upon the magnitude of the LPCR. The charge configuration in each of the scenarios represents only its vertical profile. Arrows indicate the direction of propagation of negative leader. The corresponding examples of expected electric field signatures are shown in the right panel. The field waveforms are from four different thunderstorms recorded at some tens of kilometers in Gainesville, Florida, using the same instrumentation with a decay time constant of 10 ms. PB = preliminary breakdown pulse train, RS = return-stroke waveform.

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Stolzenburg and Marshall, 2009 (1)

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Stolzenburg and Marshall, 2009 (2)

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An example of a horizontal lightning channel

traveling during a period of preliminarybreakdown

within a potential well (S&M, 2009)

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Solid ellipses denote graupel gaining positive charge, dashed ellipses indicate negative charging of graupel. Significant charge regions are noted by the shaded rectangles (light shading for net negative, darker shading for net positive charge). For inverted polarity storms, simply reverse all signs (Mansell et al., JAS, 2010).

SIMPLIFIED MODELS OF CHARGE STRUCTURES AND UNDERLYING NONINDUCTIVE CHARGE SEPARATION

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Electric potential (a) and z-component of electric eld (b) before the lightning discharge initiation

Parameters of three different cloud–charge configurations

Lightning Initiation Fractal ModelsLightning Initiation Fractal Models

References: [e.g., Niemeyer et al., IEEE Trans. Electr. Insul., 24, 309, 1989; Femia et al., J. Phys. D: Appl. Phys., 26, 619, 1993;

Petrov and Petrova, Tech. Phys., 38, 287, 1993; Petrov and Petrova, Tech. Phys., 44, 472, 1999]

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Fractal models of lightning discharge

Trakhtengerts and Iudin, 2000, 2003Pasko, 2002; Pasko and Riousset, 2007; Krehbiel et al., 2008Mansell et al., 2002; 2010

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Fractal dynamics of spritesFractal dynamics of sprites

D.Iudin, E.Mareev, V.Trakhtengerts, M.Hayakawa, Physics of Plasmas, 2007.

Thundercloud structure and discharge initiationThundercloud structure and discharge initiation

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Compact Intracloud Discharges (CIDs)

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(a) The altitude of each new node that gives rise to more than two new links for charge configuration # 1. (b) The same for charge configuration # 2; (c) the same

for charge configuration # 3

Marx generator 6 MV

The test site

control room

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Recent experiments: new diagnostic tools, including microwave absorption

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1 – steam generator, 2 – high voltage power supply, 3 – charged aerosol cloud, 4 – microwave generator, 5 – horn antenna, 6 – lenses, 7 – microwave beam, 8

– microwave detector, 9 – oscilloscopes, 10 – measuring shunt, 11 – spark discharge cloud-ground.

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IR camera FLIR CS7700 M

Diagnostic tools

High-speed optical camera 4 Picos

Crossbow bolt TenPoint TurboXLTII

LeadSledDFT

Hot plasma structures (stalkers): IR images

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Two successive frames (3a, the first and 3b, the second) taken by an IR camera, which records the upper (hidden by the aerosol) part of the upward discharge. Exposure time is 7 ms. The time between frames is 1.7 ms. The number of pixels in each frame is 640x520. All events recorded in the frame occurred inside the cloud. Only flares of scattered radiation are seen in the visible range in this experiment. 1 – the channel of the upward discharge, 2 - streamer corona, 3 - intracloud plasma structures.

The stalker as a space-stem-type structure

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Observations in IR and optics (Geophys. Res. Lett.: doi:10.1002/2015GL065620)

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Simultaneous IR and optic images of the same event. Exposure time of the FLIR 7700M camera is 8 ms. Shown in the upper left corner is a fragment of Figure depicting stalkers in the visible range. It can be seen that the contours of the

brightest stalkers are similar in both images.

Hot plasma structures: + cloud (J. Geophys. Res, Atmos.: doi:10.1002/2015JD023827)

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1 – the central plasma channel (stalker), negative leader – 2; branched stalker – 3, downward positive leader - 4, positive streamer corona – 5.

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Conclusions

We have analyze multi-scale dynamics of thunderstorm electric structure as related to high-energy radiation enhancements and lightning initiation. A special attention was paid to the lower positive charge region and its possible effects on the development of CG and IC discharges and thunderstorm ground enhancements (TGEs). Based on the graph theory, we have developed a fractal simulation code to examine the occurrence of lightning flashes of different type as a function of the cloud charge structure. We show in particular that presence of relatively intense lower positive charge region prevents the occurrence of negative CG flashes by ”blocking” the progression of descending negative leader from reaching ground. Further, based on our recent observations of electrical discharges in the artificial cloud of charged water droplets, we present the description of a complex hierarchical network of interacting channels at different stages of development (some of which are hot and live for milliseconds), which can possibly be considered as a missing link in the still poorly understood lightning initiation process.

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Positive & negative leaders. Streak photographs

Bazelyan E., Raizer Yu., 1998

Negative leader steps. Space stem

Stekolnikov I.S., Shkilev А.V., 1962

Les Renardiéres Group, 1977; Reess et al., 1995

Gorin B.N. et al., 1976

Профили электрического поля и заряда (индукционный механизм)

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Infrared images (negatives) obtained with 6.7-ms exposure that show the processes at different heights above the grounded plane (AGP) and different horizontal distances from the cloud axis: (a) The upward positive leader from the grounded sphere. No UPF is seen. (b) The upper part of the upward positive leader (lower right) and UPF (upper left), both inside the cloud. The two appear to be distinct discharge processes which interact, via their streamer zones. Relative to (a), the field of view of the IR camera was moved up and left (closer to the axis of the cloud). (c) The lower part of UPF (inside the cloud). The upward positive leader is outside the IR camera field of view, which was moved (relative to (b)) further up and left. The upward positive leader and the UPF apparently interact (outside of the field of view) via their streamer zones. (d) same as (c), but for the upper part of UPF near the central part of the cloud (see the dark formation on the left). Note that relatively faint UPF channels branch toward the axis of the cloud, but do not cross the axis. This direction of branching is opposite to that seen in (c), suggesting that UPFs extend bidirectionally.

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MCS soundings: electric field

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Electric field profiles (balloon measurements of May, 1991) and respective external current density

Shepherd R.T., W.D. Rust, and T. C. Marshall , Electric fields and charges near 0 C in stratiform

clouds, Monthly Weather Review, V.124, May 1996.

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0 0 exp( ) 1 exp( )0 0 0

I SH z zS H HEiV

Electric generators in the atmosphere: problems of parameterization

Kalinin A.V. et al., 2011; Mareeva et al., 2011

Negative leader step nature

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V. A. Rakov, The Physics of Lightning,Surveys in Geophysics, 2013

Biagi et al., JGR, 2010 Petersen and Beasley, JGR, 2013