INVESTIGADORES
BERTUCCI Cesar
artículos
Título:
Proton cyclotron waves upstream from Mars: Observations from Mars Global Surveyor
Autor/es:
N. ROMANELLI; C. BERTUCCI; D. GOMEZ; C. MAZELLE; M. DELVA
Revista:
PLANETARY AND SPACE SCIENCE
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Lugar: Amsterdam; Año: 2013 p. 1 - 9
ISSN:
0032-0633
Resumen:
We present a study on the properties of electromagnetic plasma waves in
the region upstream of the Martian bow shock, detected by the
magnetometer and electron reflectometer (MAG / ER) onboard the Mars
Global Surveyor (MGS) spacecraft during the period known as Science
Phasing Orbits (SPO). The frequency of these waves, measured in the MGS
reference frame (SC), is close to the local proton cyclotron frequency.
Minimum variance analysis (MVA) shows that these proton cyclotron
frequency waves (PCWs) are characterized in the SC frame by a
left-hand, elliptical polarization and propagate almost parallel to the
background magnetic field. They also have a small degree of
compressibility and an amplitude that decreases with the increase of the
interplanetary magnetic field (IMF) cone angle and radial distance from
the planet. The latter result supports the idea that the source of
these waves is Mars. In addition, we find that these waves are not
associated with the foreshock and their properties (ellipticity, degree
of polarization, direction of propagation) do not depend on the IMF cone
angle. Empirical evidence and theoretical approaches suggest that most
of these observations correspond to the ionion right hand (RH) mode
originating from the pick-up of ionized exospheric hydrogen. The
left-hand (LH) mode might be present in cases where the IMF is almost
perpendicular to the Solar Wind direction. PCWs occur in 62% of the time
during SPO1 subphase, whereas occurrence drops to 8% during SPO2. Also,
SPO1 PCWs preserve their characteristics for longer time periods and
have greater degree of polarization and coherence than those in SPO2. We
discuss these results in the context of possible changes in the pick-up
conditions from SPO1 to SPO2, or steady, spatial inhomogeneities in the
wave distribution. The lack of influence from the Solar Wind's
convective electric field upon the location of PCWs indicates that, as
suggested by recent theoretical results, there is no clear relation
between the spatial distribution of PCWs and that of pick-up ions.