TLE Corte June 2008 BALLOON BORNE DC AND AC ELECTRIC MEASUREMENTS IN 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, E DC and σ 4- Small scale features and electric turbulence in clouds 5- Lightning and atmospheric electric fields - Lightning detection - E DC and E AC 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. Hz 1/2 Conductivity measurements relaxation method Optical sensors - lightning detectors upward and downard fast light detectors - ODS sensor (not used in this study) Flight : August 7, UT from Niamey

TLE Corte June 2008 HV-AIRS, large scale meteorological conditions Niamey Balloon Flight

TLE Corte June HV-AIRS, Local meteorological conditions during flight 18 km Balloon position Courtesy E. Williams, MIT 20.01

TLE Corte June 2008 HVAIRS DC Electric Field E ~ V/m Conductivity at ceiling altitudes  - ~ 3  Sm-1  + ~ 2  Sm-1 Ceiling altitude ~ 22.5 km Sunset at balloon altitude DC2 lower electrode DC1 upper electrode Max E -25V/m at 6 km E DC = DC1 – DC2

TLE Corte June 2008 Power (au) HVAIRS_AMMA AC ELECTRIC FIELDS Background noise during ascent and Schumann resonnances Ascent km Ascent 20 – 22.5 km and ceiling

TLE Corte June 2008 HV-AIRS AMMA AC Electric Field power intensity in the frequency range 0-20Hz and aerosol layers

TLE Corte June km 13.5 km 14.2 km 15 km 2 17 km 18.3 km 16.2 km 3 and 4 3 HV-AIRS AMMA Quasi DC Electric Field ULF signatures and aerosol layers

TLE Corte June 2008 HV-AIRS AMMA : aerosol profile above 10 km km 2 15 km km 5 20 km km km Courtesy G. Di Donfrancesco, ENEA Aerosol Backcattering, AU

TLE Corte June 2008 H = 30 m ~ 1 V m -1 HVAIRS_AMMA Quasi-DC Electric Fields Modeling ULF signatures associated with clouds L Balloon ascent Δt ~ 50 s Time and Altitude Electric field Δt ~ 6s H ~ 30m Charged layer L

TLE Corte June 2008 L = 50 m, H = 30 m, uniform charge density Red L = 50 m, H = 30 m, charge density ~ exp(- z 2 /2h 2 ) h = H/3 Green L = 100 m, H = 30 m, uniform charge density Blue L = 100 m, H = 30 m, charge density ~ exp(- z 2 /2h 2 ) h = H/3 Black Ascent through the center of the volume Q total ~ µC For ΔE ~ 0.06 V/m

TLE Corte June 2008 HVAIRS, CHARGED CIRRUS ABOVE THE TROPOPAUSE IMPLICATIONS 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/cm 3 and effective radius 2-14 µm - Charged layers identified as stratospheric cirrus with charged ice particles Charged volume ~ cm 3, Number of particles ~ Charge on individual ice particles: ~ C - Electric Field above active thunderstorms: 1 to 10 kV/m - Electric Force: Fe = qE ~ to 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 ~ N for V ~10 m/s diameter 1 µm Fa ~ N for V ~1 m/sFa ~ N for V ~10 m/s For small ( vertical updraft force Upward transport of water to stratosphere above thunderstorms Atmospheric E-field as efficient as vertical winds for small ice particles

TLE Corte June 2008 precursors Continuing current HV-AIRS LIGHTNING and E-FIELD ΔE > 0 Precursors and Continuing currents

TLE Corte June 2008 HV-AIRS LIGHTNING and E-FIELD Precursors and Continuing Currents PrecursorsContinuing current

TLE Corte June 2008 HV-AIRS LIGHTNING and E-FIELD Δ E > 0

TLE Corte June 2008 HV-AIRS LIGHTNING and E-FIELD Δ E > 0

TLE Corte June 2008 HV-AIRS LIGHTNING and E-FIELD Δ E > 0

TLE Corte June 2008 E AC E DC Lightning HV-AIRS AMMA, LIGHTNING, EM Pulse and Transverse resonance Freqency ~ 2 kHz

TLE Corte June 2008 Transverse Resonance: frequency variation during flight

TLE Corte June 2008 HV-AIRS LIGHTNING AND ELECTRIC FIELDS SUMMARY 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 ~ 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 ~ model times - Small scale processes vs global model ? - Resistive Ionosphere?

TLE Corte June 2008 END