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H.O. Rucker - W.S. Kurth - P. Louarn - G. Fischer (Eds.)
Planetary Radio Emissions VII
Proceedings of the 7th International Workshop on
Planetary, Solar and Heliospheric Radio Emissions held at Graz, Austria, September 15–17, 2010
L. Lamy,
P. Zarka,
R. Prangé
S. 283 - 284 doi: 10.1553/PRE7s283
Verlag der Österreichischen Akademie der Wissenschaften
Abstract:
During the flyby of the Earth by Cassini in 1999, the Radio and Plasma Wave Science (RPWS) instrument recorded one month of quasi-continuous observations of Auroral Kilometric Radiation (AKR). Analyzing the Stokes parameters of incoming radio waves, we found AKR to be 100% circular left-handed (LH) or right-handed (RHW). We analyzed separately the northern - RH - emission, from the southern - LH - one with respect to the magnetic equator. AKR power variations reveal (i) a log-normal distribution at time scales of minutes, (ii) bursts of emission at time scales of a few hours, and (iii) a clear modulation at 24 hours, with a weaker modulation at 12 hours (especially visible for LH emissions). The prominent 24 h modulation is found to modulate LH and RH AKR in phase opposition. This is interpreted as being due to visibility effects related to the precession of the terrestrial magnetic dipole, making Cassini oscillate relative to the average AKR beaming pattern from each hemisphere. We accordingly quantified the AKR beaming vs explored latitudes. On time scales shorter than a few hours, LH and RH emissions are found to be correlated. This is attributed to the actual conjugacy of the corresponding sources, simultaneously turned on by substorm occurrence. The geometrical anti-correlation (at 24 h) dominates close to Earth, while the short term correlation (substorms) dominates far from Earth, where the detection threshold makes the visibility less important than the occurrence of substorms. Finally, the 12 h modulation is detected when it is not masked by strong visibility effects, i.e. for the LH emission which is observed mostly near the magnetic equator along the path of Cassini. A 12 h modulation being also observed in some geomagnetic indices, we suggest that a physical process (e.g. semi-diurnal variable efficiency of the reconnection between interplanetary and geomagnetic fields, or magnetotail oscillations) may be responsible of the observed AKR 12 h modulation.
2011/12/28 14:47:59 Object Identifier:
0xc1aa5576 0x002a1d19
Rights:All rights reserved.For questions regarding copyright and copies please contact us by email.
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The 7th International Workshop on "Planetary, Solar and Heliospheric Radio Emissions"
is the continuation of an established tradition: This PRE VII conference followed previous
successful international workshops held at Graz, Austria, in 1984, 1987, 1991, 1996, 2001,
and 2005. This 7th workshop in September 2010 offered again the unique opportunity to
discuss the observations from Cassini at Saturn and to investigate the measurements by
other spacecraft and from the ground of the Jovian, terrestrial and solar radio emissions,
also including studies on radiation from exoplanetary sources.
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