In the inner magnetosphere of a rapidly rotating planet such as Jupiter and Saturn, radial transport of plasma mainly comprises hot, tenuous plasma moving inward and cold, denser plasma moving outward. A distinctive phenomenon resulting from the drift dispersion of injecting hot plasma provides direct evidence for this convective motion. Particle instruments aboard the Cassini spacecraft, including the Magnetospheric Imaging Instrument (MIMI) and the Cassini Plasma Spectrometer (CAPS), have made numerous observations of such signatures. The statistics of the properties of such events are studied in this paper by analyzing CAPS data from 26 Cassini orbits. A statistical picture of their major characteristics is developed, including the distributions of ages, longitudinal widths, radial distances, and longitudes and local times of injection. An unexpected longitude modulation of these events appears in the old SLS longitude system, which is based on the Saturn kilometric radiation (SKR) observations by Voyager around 1980, while no such modulation seems to exist in the new SKR longitude system of the Cassini era. A Lomb periodogram analysis, however, reveals no significant periodic modulation of these events. The injection structures are found to occupy a small fraction (∼5–10) of the available longitude space.

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[1] We present the results of new laboratory experiments that provide constraints on inter bubble film thinning and bubble coalescence as a consequence of liquid expulsion by gravitational and capillary forces. To ensure dynamic similarity to magmatic systems, the experiments are at small Reynolds numbers Re ( 1 ð Þand cover a wide range of Bond numbers (10 À3Bo 10 2 ). Results indicate that at Bo < 0.25 film drainage is due to capillary forces, whereas at Bo > 0.25 gravitational forces result in film thinning. The film drainage time scale is given by t $ C ln () and is orders of magnitude faster than often assumed for magmatic systems. Here, C $ 10 is an empirical constant and is the ratio of initial film thickness to film thickness at the time of rupture and is the characteristic capillary or buoyancy time scale at values of Bo < 0.25 and Bo > 0.25, respectively.

In the inner part of a rapidly rotating magnetosphere such as that of Saturn, the major observable signature of radial plasma convection is a series of longitudinally localized injections and simultaneous drift dispersions of hot tenuous plasma from the outer magnetosphere. The Cassini Plasma Spectrometer (CAPS) and the Cassini Magnetospheric Imaging Instrument (MIMI) have observed signatures of these processes frequently, thus providing direct evidence for Saturn's magnetospheric convective motions, in which the radial transport of plasma comprises hot, tenuous plasma moving inward and cooler, denser plasma moving outward. On the basis of an extended statistical sample of these injection/dispersion events, we find that the inflow channels occupy only a small fraction (∼7%) of the total available longitudinal space, indicating that the inflow speed is much larger than the outflow speed. We assume that the plasma is largely confined to a thin equatorial sheet and calculate its thickness by deriving the centrifugal scale height profile based on the CAPS observations. We also present the radial and longitudinal dependences of flux tube mass content as well as the total ion mass between 5 and 10 Saturn radii. Combining these results, we estimate a global plasma mass outflow rate ∼280 kg/s.

Abstract. A sharp decline in electron fluxes is observed in the Mars Global Surveyor Electron Reflectometer data in conjunction with the magnetic pileup boundary. We examine the characteristics of the evolution of the electron distribution function for one orbit. We determine that the spectra can best be explained by electron impact ionization of oxygen and hydrogen. To reproduce the observed spectral evolution, we construct a model of the effects of electron impact ionization on the electron distribution function as a flow element encounters the neutral atmosphere. Using the observed post-shock electron distribution function, we are able to reproduce the observed flux attenuation. We conclude that electron impact ionization is the physical mechanism responsible for the spectral feature.