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K. Schwingenschuh (1) ,

Electric Field Transients Observed by the HUYGENS Probe in the Atmosphere of Titan: Atmospheric Electricity Phenomena or Artefacts?. K. Schwingenschuh (1) , T. Tokano (2) , I. Jernej (1) , H.U. Eichelberger (1) , G. Prattes (1) , B.P. Besser (1) ,

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K. Schwingenschuh (1) ,

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  1. Electric Field Transients Observed by the HUYGENS Probe in the Atmosphere of Titan: Atmospheric Electricity Phenomena or Artefacts? K. Schwingenschuh(1), T. Tokano(2), I. Jernej(1), H.U. Eichelberger(1), G. Prattes(1), B.P. Besser(1), V. Brown(3), M. Hamelin(4), and H.T. PWA/HASI team (1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria, (2) Institut für Geophysik und Meteorologie, Universität zu Köln, Köln, Germany, (3) IAA, Granada, Spain, (4) Université Versailles St. Quentin, CNRS/INSU LATMOS-IPSL, UPMC, 4, place Jussieu, Paris, France. 15-17.9. 2010 – PRE VII

  2. Status: Atmospheric electricity on Titan Long lasting debate about lightning on Titan(Desch 2002, Aplin 2006) No lightning detected by Voyager and CASSINI First in-situ electric field observation by HUYGENS in the atmosphere below 140 km PWA/HASI measured during 2.5 h the electric field fluctuations in one direction up to 11 kHz Schumann resonances: externally driven (Beghin 2009) or lightning (Moorente 2007) Schumann resonance and internal ocean

  3. HUYGENS descent (sketch) Schumann resonance: external driven (36 Hz) and/or lightning Electric field transients: atmospheric electric and/or parachute discharges IWF/ÖAW GRAZ 3

  4. Methods to Detect Lightning • Optical and electromagnetic orbiter observations • Sferics by PWA • Acoustic measurements • Horizontal and vertical Schumann resonances by PWA • Fair weather field

  5. HUYGENS Electric Field modes • Horizontal 2 m antenna system (RX_EL1 and RX_EL2) Vertical electric field detectable during a tilted position of the probe only • Schumann: 3-96 Hz spectra; bandwidth: 3 Hz (6 Hz below 60 km) • AC: 0 – 11.34 kHz spectra; bandwidth: 180 Hz (360 Hz below 60 km) • Each spectrum averaged from 80 single measurements • Special short-time data (‘lightning data’) from AC (available every ~5 ms) • Sensitivity ~10-3 V/m

  6. Electrical Operational Modes • Schumann: 3-96 Hz Spectra, Bandwidth: 3 Hz (6 Hz below 60 km) • AC: 0 – 11.34 kHz Spectra, Bandwidth: 180 Hz (360 Hz below 60 km) • Each spectrum averaged from 80 single measurements • Special short-time data (‘Lightning data’) from AC (available every ~5ms) • Sensitivity ~10-3 V/m

  7. AC Power & Lightning Histogram • a) Total received power in the AC frequency range up to 11.52 kHz. Pay attention to the mode change at 63 km. The mean and standard deviations of the instrument noise level are red and green, respectively • b) Maximum number of events in the LI (lightning) data, blue is the low, green the middle, and red the high frequency range. An "event" is defined as a LI value 5dB or more above the maximum instrument noise level determined from cruise checkout data. The maximum noise levels for the low frequency range are -43.68 dBV for the first mode and -38,54 dBV for the second. For the middle and high frequency ranges, they are -59.79/-54.47 dBV and -62.05/-56.88, respectively. The absolute noise in the second mode increases with the bandwidth of the frequency lines.

  8. Scatter plots of AC and Schumann • Scatter plot of the total received power in the AC frequency range up to 11.52 kHz above 63 km and the SSP tilt 2, provided by the SSP instrument • Scatter plot of the total received power in the AC frequency range up to 96 Hz (SH or Schumann range) above 63 km and the SSP tilt 2, provided by the SSP instrument

  9. Schumann Measurements • Some frequency lines from the Schumann frequency range, means and standard deviations of the cruise checkout noise are red and green, respectively. Please pay attention to the mode change at 63 km. a) 12 Hz line before and 10.5 Hz line after the mode change b) 24/22.5 Hz line c) 36/34.5 Hz line

  10. Resonance frequencies: Morente 2008 Tab. 1: Resonant frequencies and Q factors in Titan’s electromagnetic cavity (Morente etal, Evidence of electrical activity on Titan drawn from the Schumann resonances sent by Huygens probe, Icarus, 2008)

  11. Titan Atmospheric Electricity Parameters after HUYGENS • Fair weather field < 3 V/m: precipation current • ELF resonances found in the lower atmosphere of Titan (lightning, external sources) • Conducting layer observed at 65 km: 1.4 nS/m, 700 electrons/cc • Model results indicate the existence of a subsurface conducting layer of the cavity (Simoes et al., 2007) Impulsive evwents: comparison with probe tilt indicates external origin

  12. Conclusion and Future Aspects • Short-time, impulsive electric field events or electric field transients observed • The correlation between the HUYGENS tilt angle and the electric field fluctuations supports the external origin of these events compared with probe/parachute charging. • Possible explanation: electro-gravitational generator(Mareev 2008) What is needed: • charged aerosols (Hamelin 2008) • Or clouds withs charged particles (Titan lake region: Turtle 2009) • No observation of lightning by the CASSINI orbiter (Titan flyby 35) up to present (how about atmospheric discharges?) • Possible detection of temperature enhancements caused by electrical discharges in the lower atmosphere bei the Cassini infrared instruments

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