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

Juno Plasma Wave Observations at Ganymede.

The Juno Waves instrument measured plasma waves associated with Ganymede's magnetosphere during its flyby on 7 June, day 158, 2021. Three distinct regions were identified including a wake, and nightside and dayside regions in the magnetosphere distinguished by their electron densities and associated variability. The magnetosphere includes electron cyclotron harmonic emissions including a band at the upper hybrid frequency, as well as whistler-mode chorus and hiss. These waves likely interact with energetic electrons in Ganymede's magnetosphere by pitch angle scattering and/or accelerating the electrons. The wake is accentuated by low-frequency turbulence and electrostatic solitary waves. Radio emissions observed before and after the flyby likely have their source in Ganymede's magnetosphere.884711 - European Research Council; 699041X - Southwest Research Institute; Q99064JAR - Southwest Research Institute; 80NSSC20K0557 - NASAPublished versio

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