Evidence of stronger pitch angle scattering loss caused by oblique whistler-mode waves as compared with quasi-parallel waves

International audienceWave normal distributions of lower-band whistler-mode waves observed outside the plasmapause exhibit two peaks: one near the parallel direction and the other at very oblique angles. We analyze a number of conjunction events between the Van Allen Probes near the equatorial plane and Polar Orbiting Environmental Satellites (POES) at conjugate low altitudes, where lower-band whistler-mode wave amplitudes were inferred from the two-directional POES electron measurements over 30–100 keV, assuming that these waves were quasi-parallel. For conjunction events, the wave amplitudes inferred from the POES electron measurements were found to be overestimated as compared with the Van Allen Probes measurements primarily for oblique waves and quasi-parallel waves with small wave amplitudes (< ~20 pT) measured at low latitudes. This provides plausible experimental evidence of stronger pitch angle scattering loss caused by oblique waves than by quasi-parallel waves with the same magnetic wave amplitudes, as predicted by numerical calculations

A new semiempirical model of Saturn's bow shock based on propagated solar wind parameters

A new semiempirical model of Saturn's dayside bow shock is presented. The model uses observations made during the Pioneer 11, Voyager 1, and Voyager 2 flybys as well as data from the first 6 years of the Cassini mission (2004–2010) to derive the average shape of the shock surface and the variation of shock subsolar distance with solar wind dynamic pressure. The 574 bow shock crossings used to construct the model provide good local time coverage of the dayside shock surface up to latitudes of roughly 45°, allowing the three-dimensional shape of the shock surface to be investigated for the first time. Narrowband Langmuir waves observed by the Radio and Plasma Wave Science instrument are combined with propagated solar wind velocities in order to estimate the solar wind dynamic pressure associated with each of the Cassini crossings. An axisymmetric second-order surface is then fit to the resulting crossing distribution, self-consistently accounting for solar wind dynamic pressure variations. The new semiempirical model is compared with existing models of Saturn's bow shock and magnetopause, and the physical implications of the model are discussed. On the basis of these comparisons, it is proposed that the new semiempirical model is the most accurate representation of Saturn's bow shock surface to date

A survey of Galileo plasma wave instrument observations of Jovian whistler-mode chorus

A survey of plasma wave observations at Jupiter obtained by the plasma wave instrument on board the Galileo spacecraft is presented. The observations indicate that chorus emissions are observed commonly in the Jovian magnetosphere near the magnetic equator in the approximate radial range 6 < r < 10 R-J. The survey includes almost all local times but not equally sampled in radial distance due to the spacecraft trajectory. The data suggest that chorus emissions are somewhat more intense on the dayside, but this may be a result of insufficient nightside observations. The orbit of Galileo is also restricted to +/-3 degrees of the Jovigraphic equator, but the tilt of the magnetic field permits coverage of a range of magnetic latitudes of -13 degrees < lambda(mag) < +13 degrees. The similarities of chorus emissions to terrestrial observations are a good reason to speculate that Jovian chorus emission may play a significant role in the stochastic acceleration of electrons in the radial range 6-10 R-J as recent studies indicate. These electrons may then be transported inward by radial diffusion where they are additionally accelerated to form the synchrotron radiation belt source

Equatorial electron density measurements in Saturn’s inner magnetosphere

International audienceUpper hybrid resonance emissions detected by theRadio and Plasma Wave Science (RPWS) instrument on theCassini spacecraft are used to obtain electron densities onfive equatorial orbits of Saturn at radial distances rangingfrom 3 to 9 saturnian radii (RS). The electron density profilesfor these orbits show a highly repeatable radial dependencebeyond 5 RS, decreasing with increasing radial distanceapproximately as (1/R)3.63. Inside 5 RS, the electron densityprofiles are highly variable. We show that these radialvariations are consistent with a centrifugally-drivenoutward transport of plasma from a source inside 5 RS

Recurrent pulsations in Saturn’s high latitude magnetosphere

Over the course of about 6 h on Day 129, 2008, the UV imaging spectrograph (UVIS) on the Cassini spacecraft observed a repeated intensification and broadening of the high latitude auroral oval into the polar cap. This feature repeated at least 5 times with about a 1 h period, as it rotated in the direction of corotation, somewhat below the planetary rotation rate, such that it moved from noon to post-dusk, and from roughly 77° to 82° northern latitudes during the observing interval. The recurring UV observation was accompanied by pronounced ∼1 h pulsations in auroral hiss power, magnetic perturbations consistent with small-scale field aligned currents, and energetic ion conics and electrons beaming upward parallel to the local magnetic field at the spacecraft location. The magnetic field and particle events are in phase with the auroral hiss pulsation. This event, taken in the context of the more thoroughly documented auroral hiss and particle signatures (seen on many high latitude Cassini orbits), sheds light on the possible driving mechanisms, the most likely of which are magnetopause reconnection and/or Kelvin Helmholtz waves