Atmospheric Electricity on Earth and Planets

Home , Atmospheric electricity, Whistler (radio)

ATMOSPHERIC ELECTRICITY ON EARTH AND PLANETS

J.J. BERTHELIER, LATMOS/IPSL

9th International Planetary Probe Workshop, Toulouse, June 16-17, 2012.

OUTLINE (1)

TERRESTRIAL ATMOSPHERIC ELECTRICITY 1- THE GLOBAL ATMOSPHERIC CIRCUIT - The Conductive Atmosphere and Boundaries - Generators - Coupling with outer space 2- PHYSICAL PROCESSES - Charging/Discharging Mechanisms in Clouds and Thunderstorms - High Altitude Phenomena: Transient Luminous Events - Acceleration Processes: Transient Gamma Ray Flashes - EM emissions and Schumann resonances

PLANETARY ATMOSPHERIC ELECTRICITY 1- PLANETARY GLOBAL ELECTRICAL CIRCUITS - Terrestrial Planets: Venus, Mars - Giant Planets: Jupiter, Saturn and their moons 2- OBSERVATIONS OUTLINE (2)

INSTRUMENTATION 1- MEASUREMENT CONDITIONS - Ground Based Observations - Observations from Space - Balloons 2- MEASUREMENTS TECHNIQUES - Conductivity - Electric Fields and Waves 3- SOME EXAMPLES

THE EARTH’S GLOBAL ATMOSPHERIC ELECTRIC CIRCUIT

E J σ

From M.J. Rycroft et al., JASTP, 2000 ATMOSPHERIC CONDUCTIVITY

Production Mechanisms - Soil radioactivity at low altitude - Cosmic rays - Solar sources: UV, X-rays, - auroral and polar regions: magnetospheric electrons, solar protons Charged Particles - Positive and Negative cluster ions Conductivity profile -14 - 10 S/m at ground, scale height Hσ~ atmospheric scale height ~ 6-7 km - Isotropic till ~ 70 km, anisotropic in the ionosphere σ// >> σ Hall, σPedersen - day/night and latitude variations ATMOSPHERIC CONDUCTIVITY

From Hale, ASR, 1984 GENERATORS, THUNDERSTORMS

CHARGING MECHANISMS Convective air motion in thunderstorm clouds, temperature profile Collisional Charging between graupels and rain drops Electrical structure of Thunderstorm clouds

-Q

From Marshall & Rust, JGR, 1991 GENERATORS, LIGHTNING

Negative Cloud to Ground, CG-

Positive Cloud to Ground, CG+

Intracloud IC Cloud to Cloud CC GENERATORS, LIGHTNING

Geographic Average Distribution

From Christian et al, JGR 2003 GENERATORS, LIGHTNING SEASONAL VARIATIONS GENERATORS, HIGH ALTITUDE DISCHARGES, TLE’s

PHYSICAL PROCESSES TLE’s (Sprites, Blue Jets, Elves, Gigantic jets) are electrical discharges in the stratosphere and mesosphere above active thunderstorm clouds

Sprites Large Electric Field between cloud and ionosphere following a +CG Break-down threshold reached at ~ 70 km Elves Initiated from the EMP following a CG Ionization and luminous halo produced in the mesosphere at ~ 90 km Blue Jets and Gigantic Jets Streamer initiated at cloud top (~ 15-18 km) by localized intensification of the electric field Propagate up to ~40 km for BJ, ~ 70 km or GJ GENERATORS, HIGH ALTITUDE DISCHARGES, TLE’s GENERATORS, HIGH ALTITUDE DISCHARGES, TLE’s ACCELERATION PROCESSES, TGF

PHYSICAL PROCESSES Acceleration of Electrons up to ~ 100 MeV

- Relativistic Runaway Electron Avalanche from cosmic ray generated electrons initially proposed. But (i) cosmic ray showers not a sufficient electron source (ii) RREA cannot account for the intensity of TGF fluxes. - Two mechanisms recently proposed (Dwyer2007, 2008): - Relativistic Feedback mechanism from backward propagating positrons and scattered X,γ rays - Runaway Electron production in large E-fields reproduces the duration and intensity of TGF

From Dwyer, 2011 ACCELERATION PROCESSES, TGF

Simulation/Observations comparisons

Electron fluxes: RHESSI data (black dots) Simulated fluxes (red curve) (Dwyer, JGR, 2008) ELECTRO-MAGNETIC EMISSIONS

Sferics - frequency spectrum peaked at ~ 10 kHz, extends up to a few MHz Whistlers - Ionospheric propagation along Earth’s magnetic field and ducts at ELF/VLF Transverse Resonance - Between the surface and the lower ionosphere, ~ 1.5 to 3 kHz Schumann Resonances - Resonant modes of the Earth-Ionosphere wave guide ω ~ [n(n+1)]1/2 (c/R) - frequencies 7.8, 14.3, 20.8, 27.3, 33.8, … COUPLING WITH OUTER SPACE COUPLING WITH OUTER SPACE

From Rycroft, 2011 PLANETARY ATMOSPHERIC ELECTRICITY

CONDITIONS FOR A GLOBAL ELECTRICAL CIRCUIT ON OTHER PLANETS

Ion mobility in Upper Lower Clouds Electrification lower Conductive Conductive Mechanisms atmosphere Boundary Boundary Venus yes Ionosphere Yes yes Charge separation σg small Lightning

Mars yes Ionosphere σg? Faint, high Dust impact Water altitude reservoirs? Jupiter Probably not in Ionosphere ? yes Charge deep Deep layers? separation atmosphere lightning Saturn Probably not in Ionosphere ? yes Charge deep Deep layers? separation atmosphere Lightning Titan Yes, weak at Ionosphere Buried ocean yes ? Lightning not low altitude observed VENUS

Whistler mode ELF signals from the Venus Express magnetometer Indicating the existence of lightning

Russel et al., ASR 2008 MARS

Conductivity - profile similar to Earth - σ at surface ~ 103 σ on Earth Electrification Mechanism - Dust Impact - Charge depends on size, material - Breakdown at ~ 10 kV/m Molina Cuberos, 2006 Generators - Dust storms - Dust Devils Observations - SR of extremely high amplitude (?)

(Kok, Renno, 2007) SATURN

« Saturn Electronic Discharges » (SED) observed by RPWS on Cassini EM emissions from lightning SATURN and JUPITER

Comparison between Saturn, Jupiter and Earth lightning Lightning sources : - Saturn: Giant convective storm systems 3000 km in diameter, equator or 35°S - Jupiter: numerous storms in ~ 5° latitude bands at ~ 50° N and S - Updrafting water clouds at levels of ~ 10 bar (Saturn), ~ 5 bar (Jupiter) Characteristics - Frequency spectrum: up to 20 MHz / a few kHz / a few MHz - Spectral power at MHz frequencies 100 W/Hz / ~10 / 0.01 Physical process - Saturn: Elves more likely than Sprites - Jupiter: lightning a few ms long

Desch et al., 2002; Fisher et al., 2008 TITAN

36 Hz peak in ELF AC electric field spectrum interpreted as the second harmonic of Schumann resonnance of the planet-ionosphere wave-guide due to a buried ocean at ~ 60-80 km depth

Simoes et al., Icarus, 2007 Beghin et al, 2012 INSTRUMENTATION AND OBSERVATIONS

1- CONDUCTIVITY

2- ELECTRIC FIELDS AND WAVES

3- CURRENTS

4- EXAMPLES OF OBSERVATIONS - Stratospheric balloon measurements - Huygens probe measurements in the atmosphere of Titan ATMOSPHERIC ELECTRICITY PARAMETERS AND THEIR MEASUREMENTS

From M.J. Rycroft et al., JASTP, 2000

E σ J

E σ

From R.G. Harrison, Surveys in Geophysics, 2004 ATMOSPHERE ELECTRIC CONDUCTIVITY (1)

Gerdien Condenser Relaxation method Mutual Impedance I + R C TX

i+ µ<µc i+ µ>µ i+ µ=µ c c τ V R RX R

C + σ = Σ e.ni.µi Z(σ,ε) = V/I V

I Phase σ = ε0/τ = ε0RC Amplitude Amplitude

τ µ1 µ2 µ3 V t frequency ATMOSPHERE ELECTRIC CONDUCTIVITY (2)

Gerdien condenser - gives access to the ion mobility spectrum - relaxation method can be included - requires accurately controlled air flow - complexity (fan, electronics…)

Relaxation method (with electrostatic probes) - simple, can be easily implemented on double probe - accurate technique for large enough σ and stable electric field - analysis difficult with a variable background electric field - requires specific modeling in case of space charge

Mutual impedance - accurate in atmospheres with both ions and electrons - able to provide soil measurements if landed on planetary surface - complexity (booms, electronics…) TERRESTRIAL CONDUCTIVITY PROFILES

From R.H. Holzworth, JGR, 1991

From W. Gringel, Prometheus, 1977 ELECTRIC FIELD MEASUREMENTS

INDUCTIVE COUPLING RESISTIVE COUPLING THE « FIELD MACHINES » THE DOUBLE PROBE INSTRUMENT

- + ELECTRIC FIELD MEASUREMENTS

C - + s Ci Ri Rs

V1 Zg<

⎡ Zi ⎤ Vout = [(V1 −V2 )+ (WF2 −WF1 )]⋅ ⎢ ⎥ ⎣ Zi + Zs ⎦ ELECTRIC FIELD MEASUREMENTS

1 Transition frequency ωs = Rs ⋅Cs

Ri if R R Low Frequency limit Vout = (V1 −V2 )⋅ ≅ (V1 −V2 ) i >> s Ri + Rs C 1 s High Frequency Limit Z 1 Z ≈ Vout = (V1 −V2 )⋅ s ≈ C i ωC ω s i Cs + Ci

DC-ELF : spherical sensors (with polarization current) HF : cylindrical long antenna ELECTRIC FIELD MEASUREMENTS

INDUCTIVE COUPLING, THE « FIELD MACHINES » - high impedance, can operate in very low σ (Earth’s surface) - can measure large DC electric fields - Some directional capability, 2D measurement with 1 sensor - innovative designs in progress, miniaturized devices, vibrating system, ASIC - low sensitivity - electro-mechanical device (harsh environments, dust, EMI…), signal processing - low temporal resolution and low frequency capability (no waves)

RESISTIVE COUPLING, THE DOUBLE PROBE INSTRUMENT - simple device and electronics - high sensitivity (in AC better than 1µV/mHz1/2) - high temporal resolution (lightning), high frequency capability (MHz) - direct measurement, no signal processing - high amplitude DC and AC electric field measurements in dedicated modes - booms (deployment, mass,…) - limited to σ ≥ 10-13 S/m (on Earth above ~ 8 kilometers) ATMOSPHERIC CURRENT MEASUREMENTS

From A.J. Bennet and R.G. Harrison, Sub. Adv in Geosciences ELECTRIC FIELDS AND CONDUCTIVITY MEASUREMENTS ON STRATOSPHERIC BALLOON FLIGHTS

HVAIRS Gondola AMMA Campaign in Niger Electric Field Intrument 50 cm • Vertical component of Electric Field - DC to 3 kHz - Large signal « DC channel » ~ ± 50 mV/m to ± 200 V/m (up to ± 10 kV/m in special mode) - Small signal « AC channel » sensitivity ~ 30 µV/m. Hz1/2 • Conductivity measurements - relaxation method Optical sensors • photodiode lightning detectors On-Board Data Storage HVAIRS_AMMA, Meteorological Conditions (1)

Balloon flight

Niamey HVAIRS_AMMA, Meteorological conditions (2)

19.01

20.01

19.31 20.01 HVAIRS_AMMA, Conductivity Measurements

Premier mode de la sonde à relaxation Relax n° 6 Tau=23.7851 V=139.2663 V0=205.038 V1=-0.11411 V2=0 V3=0 K=2 Relax n°13 Tau=29.5881 V=117.4017 V0=174.8966 V1=0.010034 V2=0 V3=0 K=2 360 1000 180

340 4943 s, altitude 800 160 320 τ = 23.8 ± 1 s -13 600 140 300 σ = 3.7 ± 0.15 10 S/m 6023 s, altitude

400 120 280 τ = 29.6 ± 0.5 s -13 260 100 σ = 3 ± 0.1 10 S/m 200 Amplitude du champ DC champ du Amplitude DC Electric Field [1] Field Electric DC DC Electric Field [1] Field Electric DC

240

80 0

220

60 -200 200 relaxation n° 1

180 40 0 50 100 150 200 250 0.8 0.9 1 1.1 1.2 1.3 0 50 100 150 200 250 4 Time: 4943 [s] Time*2 [s] x 10 Time: 6023 [s]

20 22.5 22.5 22 34 2.5 10-13 σ- ~ 3.1 10-13 S/m 32

-13 30 σ+ ~ 3.3 10 S/m

28 -13

Tau [s]Tau σ ~ 6.4 10 S/m 26 -12 24 σ ~ 2 10 S/m R.H. Holzworth JGR, 1991

22 relaxation positive -12 relaxation négative σ ~ 1.4 10 S/m -13 From W. Gringel, Prometheus, 1977 4.5 10 20 4000 4500 5000 5500 6000 6500 7000 Time [s] 4000 5000 6000 7000 HVAIRS_AMMA, AC ELECTRIC FIELDS Background noise during ascent and Schumann resonnances

6 x 10 Intégration des FFT de chaque page des fichiers 4 à 12 (divion 15) 10 fichier4 9 Power (au) fichier5 fichier6 8 fichier7 fichier8 7 Ascent 0- 20 km fichier9 fichier10 6 fichier11 fichier12 5

4 amplitude du champ 3

6 x 10 Intégration5 des 10fft de chaque15 page 20des fichiers25 12 à 2130 (division 3515) 2.5 Fréquence [Hz] fichier12 fichier13 fichier14 2 Ascent 20 – 22.5 km fichier15 and ceiling fichier16 fichier17 fichier18 1.5 fichier19 fichier20 fichier21 ~ 8 1 Amplitude du champ du Amplitude ~ 14 ~ 20 0.5 ~ 26.5 ~ 32.5 ~ 38.5

0 0 5 10 15 20 25 30 35 40 Fréquence [Hz] HVAIRS_AMMA, LIGHTNING and DC ELECTRIC FIELDS DC Electric Fields variations induced by lightning Intra-Cloud Charge neutralization

Dejnakarintra, 1973 HV-AIRS LIGHTNING and E-FIELD Precursors and Continuing Currents

File: 27 Pages:5-5 0.3

0.2 ] 1 - 0.1

0 DC Field [Vm

-0.1

-0.2 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4

2 Lightning [1]

0 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 Time [s]

Precursors Continuing current File 8 0.2

0.15

0.1 ] 1 - 0.05

-0.05 AC Field [Vm Field AC -0.1

-0.15

-0.2 HVAIRS_AMMA, DC Electric Fields 0 50 100 150 200 250 300 350 ULF signatures of stratosphericTime [s] charged clouds

25 File 9 14.5 0.2

0.15 14

0.1 ]

1 13.5 - ] 1 - 0.0520

0 13

-0.05 12.5 [km] Altitude DC Field [Vm AC Field [Vm Field AC -0.115 -0.15 12

-0.2 0 50 100 150 200 250 300 350 11.5 0 50 100 150 200 250 300 350 Time [s] T0=17:24:49 + Time [s]

16.5 12 16 ] 1 - 10 15.5

8 [km] Altitude DC Field [Vm

14.5

6 14 0 50 100 150 200 250 300 350 T0=17:31:13 + Time [s] HVAIRS_AMMA, DC Electric Fields ULF signatures of stratospheric Charged Clouds

~ 1 V m-1

Δt ~ 50 s Δt ~ 6s Balloon ascent H ~ 30m

Electric Field [Vm-1] -0.05 -0.04 -0.03 -0.02 -0.01 0.01 0.02 0.03 0.04 0.05 -300 -300 0

Charged volume L -200 -200

H = 30 m -100

H ~ 30m Distance [m] 0 L ~ 50-100m Q~ 10-30 µC 100 200 300 HV-AIRS AMMA, LIGHTNING, EM Pulse and Transverse resonance File:25 Pages:7-7 File:27 Pages:12-12 0.8 0.04

] 0.6 ] 1 1 - - 0.02 0.4 0 0.2 -0.02 AC Field [Vm Field AC 0 [Vm Field AC -0.04 E AC Freqency ~ 2 kHz -0.2 -0.06 20 20.1 20.2 20.3 20.416.45 16.45520.5 16.46 20.6 16.465 20.716.47 16.47520.8 16.4820.9 16.485 21 16.49 16.495 16.5

1.1 1.5 ] ] 1 1 - 1 - 1

0.9 E DC DC Field [Vm DC Field [Vm 0.5 0.8 20 20.1 20.2 20.3 20.416.45 16.45520.5 16.46 20.6 16.465 20.716.47 16.47520.8 16.4820.9 16.485 21 16.49 16.495 16.5

5 5

4 4

3 3

2 2 Lightning [1]

Lightning [1] Lightning 1 1

0 0 20 20.1 20.2 20.3 20.416.45 16.45520.5 16.46 20.6 16.465 20.716.47 16.47520.8 16.4820.9 16.485 21 16.49 16.495 16.5 Time [s] Time [s] LIGHTNING DETECTION FROM ORBIT DEMETER Observations at 650 km altitude LIGHTNING DETECTION FROM ORBIT DEMETER Observations at 650 km altitude THE HASI/PWA EXPERIMENT ON HUYGENS

PWA aimed at contributing to answering the following questions: • What are the ion and electron conductivity profiles? • What is the role of aerosols in atmospheric chemistry? • Is there lightning on Titan? • Do standing waves form in the surface-ionosphere cavity? • What are the dielectric properties of the surface? • Does a global electric circuit exist on Titan? PWA ELECTRODES

Relaxation Probe RP

Mutual Impedance Probe MIP PLANETARY CONDUCTIVITY PROFILES: TITAN

HASI_PWA experiment on HUYGENS

From M. Hamelin et al., PSS, 2007. HUYGENS: Relaxation Curve with plateaus

0 0 10 20 30 Time (s) 40 50 60 RELAXATION PROBE WAVEFORMS DETECTION OF AEROSOL LAYER IN TITAN ATMOSPHERE

No artefact has been found 66 km to explain this behaviour. Plateaus likely correspond Plateaus to absence of electrons - aerosol layers or bubbles (ongoing work).

Aerosol structure 72 km Altitude [km] Thickness [km] 94.5 3.3 70 0.3 69.7 0.1 Conductivity of negative charges ~1 nS/m 62.2 0.1 57.1 0.2 54.3 0.2 56. 6 0.1 50.9 0.1 RP measured positive ions and negative ions+electrons López-Moreno et al., 2008