Ion Bulk Velocity Research Articles

Ion distributions in the dayside magnetosheaths of Jupiter and Saturn

Data from the Voyager 1 and 2 Plasma Science experiment in the dayside magnetosheaths of Jupiter and Saturn are analyzed. The ion distributions throughout the dayside magnetosheaths of both planets are well modeled by a two‐temperature proton distribution. The two proton populations have comparable densities, and temperatures of 100 and 1000 eV. Similar two‐temperature proton distributions are occasionally observed in earth's magnetosheath. Ion temperatures, densities, and bulk velocities for the four magnetosheath crossings are presented, confirming that sunward flow of up to 100 km/s occurs when the magnetosphere is expanding.

The tail lobe ion spectrometer

A two‐dimensional kinetic “tail lobe ion spectrometer” model for the transport of ionospheric ions from the polar cleft ionosphere into the tail lobes is developed to semiquantitatively simulate the behavior of the observed O+ ion streams in the magnetotail lobes. The consequences of the present model include (1) the increase in velocity of the O+ streams away from the tail midplane; (2) the existence of “tongues” of O+ density from the cleft ionosphere into the tail lobes whose distribution configuration depends on the convection electric field and the source thermal energies; and (3) very low parallel thermal energies and speeds in the lobes which are correlated with the parallel ion bulk velocities. These consequences are reasonably consistent with the trends in lobe streams observed by recent spacecraft.

The Venus ionosphere at grazing incidence of solar radiation: Transport of plasma to the night ionosphere

Using a quasi-two-dimensional model of the Venus ionosphere, we calculated the ion number densities and horizontal ion bulk velocities expected for a range of solar zenith angles near the terminator (80 to 100°), and compared them with data obtained from the Pioneer Venus Orbiter retarding potential analyzer. The calculated ion bulk velocity arises entirely from the solar EUV-induced plasma pressure gradient and has a magnitude consistent with observations; ionization by suprathermal electrons is neglected in those computations. We find that while photoionization is the dominant source of ionospheric plasma for solar zenith angles less than 92°, plasma transport from the dayside is the dominant plasma source for solar zenith angles greater than 95°. We also show that the main nightside plasma peak at approximately 140 km altitude is of the F 2 type (i.e., is diffusion controlled). Its altitude and shape are thus quite insensitive to the altitude of the ion source.