IAFE   05512
INSTITUTO DE ASTRONOMIA Y FISICA DEL ESPACIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Saturn's ULF wave foreshock boundary: Cassini observations
Autor/es:
NAHUEL ANDRÉS; DANIEL O. GOMEZ; CESAR BERTUCCI; CHRISTIAN MAZELLE; MICHELLE DOUGHERTY
Lugar:
Paris
Reunión:
Workshop; 8th European Workshop on Collisionless Shocks; 2013
Resumen:
Even though the solar wind is highly supersonic, intense ultra-low frequency (ULF) wave activity
has been detected in regions just upstream of the bow shocks of magnetized planets. This feature
was first observed ahead of the Earths bow shock, and the corresponding region was called the
ULF wave foreshock, which is embedded within the planets foreshock. The properties as well as
the spatial distribution of ULF waves within the Earths foreshock have been extensively studied
over the last three decades and have been explained as a result of plasma instabilities triggered by
solar wind ions backstreaming from the bow shock. Since July 2004, the Cassini spacecraft has
characterized the Saturnian plasma environment including its upstream region. Since Cassinis
Saturn orbit insertion (SOI) in June 2004 through August 2005, we conducted a detailed survey
and analysis of observations made by the Vector Helium Magnetometer (VHM). The purpose
of the present study is to characterize the properties of waves observed in Saturns ULF wave
foreshock and identify its boundary using single spacecraft techniques. The amplitude of these
waves is usually comparable to the mean magnetic field intensity, while their frequencies in the
spacecraft frame yields two clearly differentiated types of waves: one with frequencies below the
local proton cyclotron frequency (ΩH+ ) and another with frequencies above ΩH+ . All the wave
crossings described here, clearly show that these waves are associated to Saturns foreshock. In
particular, the presence of waves is associated with the change in θBn to quasi-parallel geometries.
Our results show the existence of a clear boundary for Saturns ULF wave foreshock, compatible
with θBn ∼ 45 degree surfaces.