INVESTIGADORES
BERTUCCI Cesar
artículos
Título:
Saturn's ULF wave foreshock boundary: Cassini observations
Autor/es:
N. ANDRÉS; D. GOMEZ; C. BERTUCCI; C. MAZELLE; M. DOUGHERTY
Revista:
PLANETARY AND SPACE SCIENCE
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Lugar: Amsterdam; Año: 2013 p. 64 - 75
ISSN:
0032-0633
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 Earth's bow shock, and the corresponding region was called
the ULF wave foreshock, which is embedded within the planet's foreshock.
The properties as well as the spatial distribution of ULF waves within
the Earth's 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 Cassini's 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 Saturn's 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 different types of waves: one with frequencies below the local
proton cyclotron frequency (Ω) and another with
frequencies above Ω. All the wave crossings described
here, clearly show that these waves are associated to Saturn's
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 Saturn's ULF wave
foreshock, compatible with θBn∼45° surfaces.