Atmospheric Electricity on Earth and in the Solar System...

Introduction Thunderstorm Lightning Physics Lightning Observations Lightning Electromagnetic Signatures References

Atmospheric Electricity on Earth and in the Solar SystemEAS 4803/8803: Physics of Planets

Jeremy A. Riousset ([email protected]) Carol S. Paty

School of Earth and Atmopsheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

October 19, 2011

Riousset and Paty Atmospheric Electricity 1/30


Outline

1 Introduction: Global Electrical Circuit

2 The Thunderstorm: Source of the Global Electrical Cir-cuit

3 Lightning Physics

4 Lightning Observations

5 Lightning Electromagnetic Signatures



Outline


2 The Thunderstorm: Source of the Global Electrical Circuit

3 Lightning Physics





Figure: Schematic of various electrical processes in the global electrical circuit [13, p. 6].



Figure: Role of thunderstorms in the global electrical circuit. Under the thundercloudare precipitation lightning and corona [9, p. 10].

fair weather current ∼1 kA

fair weather conductivity ∼5 × 10−14e

z

8.4 km S/m

fair weather electric field ∼100 V/m

lightning initiation electric field ∼1–2×ez

6 km kV/cm



Outline



3 Lightning Physics





Formation and electrification of the cumulonimbus (thundercloud)

∼2000 thunderstorms on Earth at any time [9, p. 10]

≳10% of Earth surface [9, p. 10]

dominant generator in the global circuit [13, p. 6]

Figure: Video courtesy of Dean Gill. Figure: Video courtesy of Daryl Herzmann.



Thunderstorm cycle

a cumulus stageb mature stagec decaying stage

Figure: Schematic description of a typical cell of an air-mass thunderstorm in threestages of its life cycle. Arrows indicate wind directions. From http://www.noaa.gov/,adapted from [14].


http://www.noaa.gov/


Thunderstorm electrification

Figure: Schematic of the collisional charging mechanism [9, p. 86].



Thundercloud electrical structure

Layered structureSize and height vary (e.g., maritime vs continental clouds)Lightning occur every few seconds to every few minutes

Uppernegativecharge

Upperpositivecharge

Mainnegativecharge

Lowerpositivecharge

-25oC-25oC

0oC0oC

Updraft

+ ++ + + ++ + + + +

+ + + + + ++ + + + +

+++++++

++

+

+++

++

++

+++

++

++

++

+ ++

++

++

++

+++ +

++

+

++

+++

+ +++

++

++++

+ +++++

++++

+ +++++

+++

+ + +++

++++++++++++ ++++++

+++++++

+ + ++++

+ ++ ++ +++ ++ + +++++++ ++ ++ ++ +

++ + +

–––––––––

–––––

–––––

––––––

––––––

––––– ––––

––––––– –––– ––––– –––– –

–––––––––

––––––

–––– ––

––––– ––––––

––––––

–––––

––––– ––––––

––––– ––––

––––––––––––––

–––––––

–––

–––––––

–––––

–––– –––––

––

––– ––––– –––––– ––––– ––––––– ––

–– –––– – ––––––– – –––––– ––––

–––––––––

––– ––

–––––––––

–– ––––

Figure: Schematic of the basic charge structure in the convective region of a thunder-storm [12; 9, p. 83].



Outline



3 Lightning Physics





The lightning diversity

Intra-cloud, cloud-to-ground, “cloud-to-ionosphere” (jets), cloud-to-cloud...

Positive or negative

Single or multi-strokes

Stepped or continuous

Figure: (a)–(f) Intracloud, cloud-to-ground, low intracloud, positive blue jet, bolt-from-the-blue, negative gigantic jets. Blue and red contours and numbers indicate negativeand positive charge regions and charge amounts (in C). A partially analogous set ofdischarges occurs or would be predicted to occur in storms having inverted electricalstructures [5].



Plasma nature of lightning

Bidirectional discharge

Equipotential channel

Overall neutral during propaga-tion

Mostly hot (≳5000 K), highlyconductive

Initiated by high electric field

Reduce charge content in the ap-propriate layers

Leader channel:T>1500 KComplete detachment of negative ionsE~1 kV/cm

Leader corona:Streamer filamentsT~300 KAttached electronsLow conductivityE~5 kV/cm

Transition region:300 K<T<1500 K

Corona front:Active streamer headsHigh space charge fieldAvalanches + photoion-ization

Figure: Sketch of the leader/leader-corona system, withthe main characteristics of the different discharge regions[2].



Propagation of positive lightning channel [10]

“Natural” lightning = bidirectional system

Positive end simpler than negative end

Positive end usually not visible

Recoil negative event can develop in the positive channel

+U

(a) (b) (c)

(d) (e) (f)

+UE~5 kV/cm

2E~5 kV/cm

E~5 kV/cm

1

3

1 leader tip

2 leader channel

3 streamer zone



Propagation of negative lightning channel [10]

1 leader tip

2 primary leader channel

3 negative streamers in thestreamer zone

4 space stem or plasma spot

5 negative streamers of thestreamer zone associated withthe negative space leader

6 space leader developing from theplasma spot

7 positive streamers of thestreamer zone associated withthe positive space leader

8 negative end of the space leader

9 positive end of the space leader

10 leader step

11 burst of negative streamers

–U –U

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

+–

E~ –12.5 kV/cm E~ –12.5 kV/cm

E~ –12.5 kV/cm

E > 5 kV/cm

1

5

2

3

+–

77

98

10

11

4 6

+–

+–



Phenomenology of a –CG [3; 4; 9, p. 110]

1 Intial “stepped” negative leaderdeveloping downward

2 Upward connecting leader

3 Attachment

4 First return stroke

5 “Disconnection” from theground

6 “Dart” continuous leader

7 Second return stroke

8 etc.



Two –CG captured at 7,207 images per second

Figure: Video courtesy of Tom Warner www.ztresearch.com.

Can you recognize the following features?

Descending stepped leader

Upward connecting leader (why?)

Return stroke



Descending stepped leader

First return stroke

First, second,... dart leaders

Second, third,... return strokesRiousset and Paty Atmospheric Electricity 17/30

www.ztresearch.com

www.ztresearch.com

www.ztresearch.com

www.ztresearch.com


High speed videos of +CG and +GC

A +CG filmed at 7,207 images per second



Descending leaders (weakly luminous)

Bright, short duration recoil leaders onthe weak positive leader channels

Return stroke

A +GC filmed at 7,207 images per second



Ascending leader

Recoil events


www.ztresearch.com

www.ztresearch.com

www.ztresearch.com

www.ztresearch.com


Outline



3 Lightning Physics





Lightning Mapping Array [11]

Lightning properties:

Wide spectrum

Noisier negative than positive channels

Recoil events in negative channels

Detection method:

Detect 60–66 MHz radiation

Measure TOA at 6 or more stations

Triangulate signal

Products:

3-D time dynamic map of lightning

In and out of the cloud

“Guesstimate” of the polarity of thechannels

-6 -4 -2 0 2 4

-6 -4 -2 0 2 4East-West distance (km)

0

2

4

6

8

10

No

rth

-So

uth

dis

tan

ce

(km

)

4

6

8

10

12

Altitu

de

(km

)

-6 -4 -2 0 2 4

4 6 8 10 12

Altitude (km)

19990731

22:23:19.5 22:23:19.6 22:23:19.7 22:23:19.8

4

6

8

10

12

Altitu

de

(km

)

469 pts

alt-histogram

(d) (e)

(b) (c)

(a)

4

6

8

10

12

0

2

4

6

8

10



Electrical structure of the Cb (part. 2) [8]

Principles:

Channels propagate preferentially in re-gion of higher charge densities

Positive channels propagate in negativeregions

Negative channels propagate in positiveregions

Frequency: several flash/min

Products:

3-D time-integrated electrical structureof the cloud

complements/confirms balloon rocketsoundings



Balloon and rocket soundings [6; 7]

ρ = ε∆Ez

∆zDo you see any limita-tions?



Outline



3 Lightning Physics





Lightning electromagnetic signatures

3 ranges

spherics (or atmospherics): VLF (3–30 kHz)

Schumann resonance: ELF (3 Hz–3 kHz)

whistlers: ELF and VLF (100 Hz –10 kHz)



Schumann resonance

Resonant spherical cavity [9, p. 452]

TEM wave

λ = R⊕N→ resonance

E = Er(r , ϕ, θ)rB = Bφ(r , ϕ, θ)ϕk = kθ θ

(∇2 + k2)Er = 0

Er,(m,n,l) = (A1jn(kr) +B1nn(kr))´¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¶spherical Bessel func.

Pmn (cos(θ))´¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¶

assoc. Legendre poly.

(C3 sin(mϕ)+D3cos(mϕ))

[1, p. 557]

fn = c

2πR⊕

√n(n + 1)



Whistler wave

Figure: Typical path of a ducted whistler within the plasmasphere [9, p. 435].



Whistler wave

Possible if ω < ωpe = q2nemeε0

, ωce = qB0

me

Ducted by the inner electron belt

High frequencies propagate faster thanlower frequencies → “chirp”

Acoustic frequencies but not in audiblerange

Processed like radio signals from a radiostation

Figure: Courtesy of Donald A. Gurnett, Univ. ofIowa.

http://www-pw.physics.uiowa.edu/plasma-wave/istp/polar/magnetosound.html


http://www-pw.physics.uiowa.edu/plasma-wave/istp/polar/magnetosound.html


Lightning in the solar system

Schumann resonances [15] and whistlers[9, p. 530] as proxies

Available data for Venus, Jupiter, Sat-urn, Uranus, Neptune [9, p. 530]

Possible electrical discharges on Mars,Titan

What problems do you see?

PlanetType of data Venus Jupiter Saturn Uranus NeptuneOptical ✓ ✓Whistlers ✓ ✓ ✓RF ✓ ✓ ✓ ✓ ✓

[9, Table 16.1]Riousset and Paty Atmospheric Electricity 28/30


Acknowledgements

Thank You For Your AttentionQuestions?



References

[1] C. A. Balanis. Advanced Engineering Electromagnetics. John Wiley & Sons, Inc., New York, NY, 1989.

[2] D. Comtois, H. Pepin, F. Vidal, F. A. Rizk, C. Y. Chien, T. W. Johnston, J. C. Kieffer, B. La Fontaine, C. Potvin, P. Couture, H. P.Mercure, A. Bondiou-Clergerie, P. Lalande, and I. Gallimberti. Triggering and guiding of an upward positive leader from a ground rodwith an ultrashort laser pulse–II: Modeling. IEEE Trans. Plasma Sci., 31(3):387–395, 2003. doi: 10.1109/TPS.2003.811649.

[3] R. H. Golde. Lightning, volume 1: Physics of Lightning. Academic Press, London, UK; New York, NY, 1977.

[4] R. H. Golde. Lightning, volume 2: Lightning Protection. Academic Press, London, UK; New York, NY, 1977.

[5] P. R. Krehbiel, J. A. Riousset, V. P. Pasko, R. J. Thomas, W. Rison, M. A. Stanley, and H. E. Edens. Upward electrical dischargesfrom thunderstorms. Nature Geoscience, 1(4):233–237, 2008. doi: 10.1038/ngeo162.

[6] T. C. Marshall, W. Rison, W. D. Rust, M. Stolzenburg, J. C. Willett, and W. P. Winn. Rocket and balloon observations of electricfield in two thunderstorms. J. Geophys. Res., 100(D10):20815–20828, 1995. ISSN 0148-0227. doi: 10.1029/95JD01877. URLhttp://dx.doi.org/10.1029/95JD01877.

[7] T. C. Marshall, W. D. Rust, and M. Stolzenburg. Electrical structure and updraft speeds in thunderstorms over the southern greatplains. J. Geophys. Res., 100(D1):1001–1015, 1995. ISSN 0148-0227. URL http://dx.doi.org/10.1029/94JD02607.

[8] T. C. Marshall, M. Stolzenburg, C. R. Maggio, L. M. Coleman, P. R. Krehbiel, T. Hamlin, R. J. Thomas, and W. Rison. Observedelectric fields associated with lightning initiation. Geophys. Res. Lett., 32(3):L03813, 2005. doi: 10.1029/2004GL021802.

[9] V. A. Rakov and M. A. Uman. Lightning: Physics and Effects. Cambridge Univ. Press, Cambridge, U.K.; New York, NY, 2003.

[10] J. A. Riousset. Numerical modeling of lightning, blue jet, and gigantic jets. PhD thesis, The Pennsylvania State University,University Park, PA, August 2010.

[11] W. Rison, R. J. Thomas, P. R. Krehbiel, T. Hamlin, and J. Harlin. A GPS-based three-dimensional lightning mapping system: Initialobservations in central New Mexico. Geophys. Res. Lett., 26(23):3573–3576, 1999. doi: 10.1029/1999GL010856.

[12] M. Stolzenburg, W. D. Rust, and T. C. Marshall. Electrical structure in thunderstorm convective regions–1. Mesoscale convectivesystems. J. Geophys. Res., 103(D12):14059–14078, 1998. doi: 10.1029/97JD03546.

[13] US National Research Council and American Geophysical Union. The Earth’s electrical environment: Based on papers presented atthe American Geophysical Union meetings in June 1983. National Academy Press, Washington, DC, 1986. ISBN 0309036801.Geophysics Study Committee, Geophysics Research Forum, Commission on Physical Sciences, Mathematics, and Resources, NationalResearch Council.

[14] J. M. Wallace and P. V. Hobbs. Atmospheric Science, An Introductory Survey, volume 92 of International Geophysics. AcademicPress, New York, NY, 2nd edition, 1973.

[15] H. Yang, V. P. Pasko, and Y. Yair. Three-dimensional finite-difference time-domain modeling of Schumann resonance parameters onTitan, Venus, and Mars. Radio Sci., 41:RS2S03, 2006. doi: 10.1029/2005RS003431.


http://dx.doi.org/10.1029/95JD01877

http://dx.doi.org/10.1029/94JD02607

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