Saturn's ULF foreshock boundary: Cassini observations

ANDRÉS, NAHUEL; BERTUCCI, CESAR; GOMEZ, DANIEL; DOUGHERTY, MICHELLE

San Francisco

Congreso; AGU Fall Meeting 2011; 2011

American Geophysical Union (AGU)

In spite of the fact that the solar wind is highly supersonic, intense ULF wave activity has been detected in regions just upstream of the bow shocks of magnetized planets such as the Earth or Saturn. This phenomenon was first observed ahead of the Earth´s bow shock, and the corresponding region was called the ULF foreshock, which is embedded into the magnetic foreshock. Its location as well as the properties of these waves have been intensely studied over the last three decades, and are expected to be the result of plasma instabilities triggered by ion beams travelling upstream from the bow shock. The purpose of the present study is to characterize the properties of waves observed in Saturn´s ULF foreshock by the VHM magnetometer on board of the Cassini-Huygens spacecraft. The amplitude of these waves is a fair fraction of the local magnetic field intensity, while their frequencies are comparable or somewhat smaller than the local ion-cyclotron value. Using VHM  data from 2004 to 2005 and following a procedure similar to the one used for the Earth´s foreshock, we manage to identify the outer boundary of Saturn´s ULF foreshock.