TLE Corte June 2008

BALLOON BORNE DC AND AC ELECTRIC MEASUREMENTSIN THE VICINTY OF TROPICAL CONVECTIVE CLOUDS.

J.J. BERTHELIER 1, F. SIMOES 1, J.P. POMMEREAU 2

1 CETP/IPSL, 2 SERVICE D’AÉRONOMIE/IPSL

TLE Corte June 2008

Overview of the presentation

1- Objectives and description of the HV-AIRS experiment

2- Meteorological conditions during flight

3- Global parameters of atmospheric electricity, EDC and σ

4- Small scale features and electric turbulence in clouds

5- Lightning and atmospheric electric fields- Lightning detection- EDC and EAC variations associated with lightning

6- Summary and conclusions

TLE Corte June 2008

HV-AIRS, Instrumentation

Double-Probe Electric Field Instrument

Vertical component of Electric Field, DC to 4 kHz - Large signal « DC channel » DC to 2 kHz from ~ ± 50 mV/m to ± 200 V/m(up to ± 10 kV/m in special mode)- Small signal « AC channel » 4 Hz to 4 kHz noise level ~ 30 µV/m. Hz1/2

Conductivity measurements relaxation method

Optical sensors

- lightning detectors upward and downard fast light detectors - ODS sensor (not used in this study)

Flight : August 7, 2006 16.45-20.00 UT from Niamey

TLE Corte June 2008

HV-AIRS, large scale meteorological conditions

Niamey

Balloon Flight

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18.01 19.31 19.0118.31

HV-AIRS, Local meteorological conditions during flight

18 km

Balloon position

Courtesy E. Williams, MIT

20.01

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DC Field 1

DC Field 2

DC1-DC2

HVAIRS DC Electric Field

E ~ - 2.5 V/m

Conductivity at ceiling altitudes

- ~ 310-13 Sm-1+ ~ 210-13 Sm-1

Ceiling altitude ~ 22.5 km Sunset at balloon altitude

DC2 lower electrode

DC1 upper electrode

Max E -25V/m at 6 km

EDC = DC1 – DC2

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Intégration des FFT de chaque page des fichiers 4 à 12 (divion 15)

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Power (au)

HVAIRS_AMMA AC ELECTRIC FIELDSBackground noise during ascent and Schumann resonnances

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Ascent 0- 20 km

Ascent 20 – 22.5 kmand ceiling

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1420 26.5 32.5 38.5

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Alti

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AC Power SpectrumFiltered SpectrumAerosols concentration

HV-AIRS AMMA AC Electric Field power intensity in the frequency range 0-20Hz

and aerosol layers

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HV-AIRS AMMA Quasi DC Electric Field ULF signatures and aerosol layers

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HV-AIRS AMMA : aerosol profile above 10 km

1 12.5 km

2 15 km

4 18.4 km

5 20 km

6 21.2 km

3 16.8 km

Courtesy G. Di Donfrancesco, ENEA

Aerosol Backcattering, AU

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H = 30 m ~ 1 V m-1

HVAIRS_AMMA Quasi-DC Electric FieldsModeling ULF signatures associated with clouds

L

Balloon ascent

Δt ~ 50 s

Time and Altitude

Electric field

Δt ~ 6sH ~ 30m

Charged layer

L

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L = 50 m, H = 30 m, uniform charge density RedL = 50 m, H = 30 m, charge density ~ exp(- z2/2h2) h = H/3 Green L = 100 m, H = 30 m, uniform charge density Blue L = 100 m, H = 30 m, charge density ~ exp(- z2/2h2) h = H/3 Black

3002001000 -100 -200 -300 -0.05

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Ascent through the center of the volume

Q total ~ + 1.5 µCFor ΔE ~ 0.06 V/m

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HVAIRS, CHARGED CIRRUS ABOVE THE TROPOPAUSEIMPLICATIONS FOR STRATOSPHERIC WATER

- Electrically charged layers detected above the tropopause (~16.5 to 18 km) horizontal dimensions ~ 40 m, thickness ~ 30 m, total average charge ~+50 µC- Geophysica flight data (courtesy de Reus, MPI Mainz) within ~ 1-2 days Aerosols with average density ~ 0.01/cm3 and effective radius 2-14 µm

- Charged layers identified as stratospheric cirrus with charged ice particles

Charged volume ~ 5 1010 cm3, Number of particles ~ 5 108

Charge on individual ice particles: ~ 10-13 C

- Electric Field above active thunderstorms: 1 to 10 kV/m

- Electric Force: Fe = qE ~ 10-10 to 10-9 N

- Atmospheric drag force: Re < 1 thus Fa ~ 6π.µ.r.V (assuming spheres)

diameter 10 µm Fa ~10-9 N for V ~1 m/s Fa ~ 10-8N for V ~10 m/s

diameter 1 µm Fa ~10-10 N for V ~1 m/s Fa ~ 10-9N for V ~10 m/s

For small (< 1µ) particles, electric force > vertical updraft force

Upward transport of water to stratosphere above thunderstorms

Atmospheric E-field as efficient as vertical winds for small ice particles

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precursors Continuing current

HV-AIRS LIGHTNING and E-FIELD ΔE > 0

Precursors and Continuing currents

TLE Corte June 2008

HV-AIRS LIGHTNING and E-FIELDPrecursors and Continuing Currents

Precursors Continuing current

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Δ E > 0

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Δ E > 0

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Lightning

HV-AIRS AMMA, LIGHTNING, EM Pulse and Transverse resonance

Freqency ~ 2 kHz

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Transverse Resonance: frequency variation during flight

TLE Corte June 2008

HV-AIRS LIGHTNING AND ELECTRIC FIELDSSUMMARY

AC ELECTRIC FIELDS

- EM pulse followed by oscillations at frequency ~ 2 kHz, Transverse Resonance

Quasi DC ELECTRIC FIELDS- Main Lightning: Step-like variation of the vertical electric field

- average ampltude ~ 0.1-0.2 V/m- rise time ~ 5 to 10 ms,- recovery time: exponential decay with time constant ~ 0.5 s

- Precursors and Continuing Currents: similar or larger effects- Comparison with Rycroft et al. (JASTP 2007) model

- ΔE > 0 : negative CG lightning, almost all cases- ΔE < 0 : positive CG lightning, a few cases- ΔE = 0 : IC or CC lightning (?)- [recovery time] / [rise time] ~ 20 to 40- measured amplitudes > 100 model amplitudes- measured rise and recovery times ~ 10-3 model times

- Small scale processes vs global model ?- Resistive Ionosphere?

TLE Corte June 2008

END