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Farrell William M., Kaiser Michael L., Fischer Georg, Zarka Philippe, Kurth William S., Gurnett Donald A.

Are Saturn electrostatic discharges really superbolts? A temporal dilemma

Geophysical Research Letters, 2007, vol. 34, pp. 06202

Référence DOI : 10.1029/2006GL028841
Référence ADS : 2007GeoRL..34.6202F

Résumé :

Saturn electrostatic discharges (SED) are freely-propagating radio emissions detected in the high frequency (HF) radio band (1-40 MHz) associated with electrical discharge (i.e., lightning) from storms in Saturn's atmosphere. While SEDs responsible for the RF emission are considered to be very energetic superbolts (>10<SUP>13</SUP> J), this determination is intimately related to the temporal nature of the discharge itself. As we demonstrate, if we assume the discharge has similar temporal properties as terrestrial cloud-to-ground discharges (with a stroke time scale ~70 mus), then indeed the discharge energy has to be ~ 10<SUP>13</SUP> J in order account for the Cassini-observed radiated HF power of ~50 W/Hz. However, if the discharge duration is faster than the terrestrial case (i.e., ~1 mus), the energy of the discharge can be weaker than the terrestrial case since the central peak of the emission shifts closer to the HF band. Because of the near-flat SED spectra measured in the HF which favors a faster discharge, we conclude that the high level of radiated HF power from SEDs may have less to do with any extreme super-bolt strength of the discharge and has more to do with the intrinsic quick time-scale of relatively weaker discharges.

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