VG2 NEP PLS DERIVED RDR 2 PROTON MAGSPHERE 48SEC V1.0

This data set gives the best available values for ion densities, temperatures, and velocities near Neptune derived from data obtained by the Voyager 2 plasma experiment. All parameters are obtained by fitting the observed spectra (current as a function of energy) with Maxwellian plasma distributions, using a non-linear least squares fitting routine to find the plasma parameters which, when coupled with the full instrument response, best simulate the data. The PLS instrument measures energy/charge, so composition is not uniquely determined but can be deduced in some cases by the separation of the observed current peaks in energy (assuming the plasma is co-moving). In the upstream solar wind protons are fit to the M-long data since high energy resolution is needed to obtain accurate plasma parameters. In the magnetosheath the ion flux so low that several L-long spectra (3-5) had to be averaged to increase the signal-to-noise ratio to a level at which the data could be reliably fit. These averaged spectra were fit using two proton maxwellians with the same velocity. The values given in the upstream magnetosheath are the total density and the density-weighted temperature. In both the upstream solar wind and magnetosheath full vector velocities, densities and temperatures are derived for each fit component. In the magnetosphere spectra do not contain enough information to obtain full velocity vectors, so flow is assumed to be purely azimuthal. In some cases the azimuthal velocity is a fit parameter, in some cases rigid corotation is assumed. In the 'outer' magnetosphere (L>5) two distinct current peaks appear in the spectra H+ and N+. In the inner magnetosphere the plasma is hot and the composition is ambiguous, although two superimposed Maxwellians are still required to fit the data. These spectra are fit using two compositions, one with H+ and N+ and the second with two H+ components. The N+ composition is preferred by the data provider. All fit values in the magnetosphere come with one sigma errors. It should be noted that no attempt has been made to account for the spacecraft potential, which is probably about -10 V in this region and will effect the density and velocity values. In the outbound magnetosheath and solar wind both moment and fit values are given for velocity, density, and thermal speed. The signal-to-noise ratio in the M-longs is very low, especially near the magnetopause, which can result in the analysis giving incorrect values. The L-long spectra have too low an energy resolution to permit accurate determinations parameters in many regions temperature and non-radial velocity components may be inaccurate.