Data Set Overview : The electron spectra are fit using several isotropic Maxwellian distribution functions to find electron parameters. The spacecraft charge may seriously affect the density measurements. The temperature of each component is, however, independent of the spacecraft potential. To obtain the best estimate of the electron density, the encounter period is divided into four regions and four different analysis methods are used. Parameters : Derived Parameters ------------------ Sampling Parameter Name : time Sampling Parameter Resolution : n/a Minimum Sampling Parameter : unk Maximum Sampling Parameter : unk Sampling Parameter Interval : unk Minimum Available Sampling Interval : unk Data Set Parameter Name : electron density Noise Level : unk Data Set Parameter Unit : cm**-3 Electron density: A derived parameter equaling the number of electrons per unit volume over a specified range of electron energy. Different forms of electron density are derived distinguished by method of derivation (Maxwellian fit, method of moments) or by the some selection criteria (i.e., hot electron and cold electron density). In general, if more than one electron component is analyzed, either by moment or fit, a total density will be provided which is the sum of the electron densities. If the electron do not have a Maxwellian distribution the actual distribution can be represented as the sum of several Maxwellians, in which case the density of each Maxwellian is given. Sampling Parameter Name : time Sampling Parameter Resolution : n/a Minimum Sampling Parameter : unk Maximum Sampling Parameter : unk Sampling Parameter Interval : unk Minimum Available Sampling Interval : unk Data Set Parameter Name : electron temperature Noise Level : unk Data Set Parameter Unit : eV Electron temperature: A derived parameter giving an indication of the mean energy/electron, assuming the shape of the electron energy spectrum to be Maxwellian (i.e. highest entropy shape). Given that the electron energy spectrum is not exactly Maxwellian, the electron temperature can be defined integrally (whereby the mean energy obtained by integrating under the actual electron energy spectrum is set equal to the integral under a Maxwellian, where the temperature is a free parameter for which to solve), or differentially (whereby the slopes of the actually electron energy spectrum at various energies are matched to the slopes of a corresponding Maxwellian). The temperature parameter is often qualified with a range of applicable energies. Temperatures can be angularly anisotropic. If the electrons do not have a Maxwellian distribution the actual distribution can be represented as the sum of several Maxwellians, each with a separate temperature. Derived Parameters ------------------ Electron Rate: A measured parameter equaling the number of electrons hitting a particle detector per specified accumulation interval. The counted electrons may or may not be discriminated as to their energies (e.g. greater than E1, or between E1 and E2). Electron Current: A measured parameter equaling the rate at which negative charge is collected by a particle detector. The electrons contributing to this current may be restricted by energy. Electrons always have a charge of 1, so this quantity corresponds directly to the electron rate. References : Zhang, M., J. D. Richardson, and E. C. Sittler, Jr., Voyager 2 electron observations in the Magnetosphere of Neptune, J. Geophys. Res., in press, 1991. J. W. Belcher, H. S. Bridge, et al., Plasma Observations Near Neptune: Initial Results from Voyager 2, Science, 246, 1478-1483, 1989. Scudder, J. D., E. C. Sittler, Jr. and H. S. Bridge, A survey of the plasma electron environment of Jupiter: a view from Voyager, J. Geophys. Res., 86, 8319-8342, 1981. Sittler, E. C., Jr., K. W. Ogilvie and R. S. Selesnick, Survey of electrons in the Uranian magnetosphere: Voyager 2 observations, J. Geophys. Res., 92, 15,263-15,281, 1987.

Confidence Level Overview : The electron parameters are reliable except near closest approach where the electrons are cold. In the time period between 237.03180 and 237.11253, the cold component is below the threshold the PLS measurement. A temperature of 3 eV is assumed for the cold component. The spacecraft potential is not determined and is set equal to zero. The parameters of the hot electron components are obtained directly from the fits and are reliable. The cold electron density is set equal to the total ion density minus the hot electron density. In this region the results have large error bars. Data Quality and Coverage : In the time period from 1989-08-24T14:38:04.130 (236.60977) to 1989-08-24T19:45:17.571 (236.82312), when the spacecraft is in the inbound magnetosheath and is probably positively charged, a program written by Sittler (1987) is used to derive the electron density and temperature. The spacecraft potential is calculated by using Scudder's (1981) return current-spacecraft potential relation. Estimates of the formal errors are not performed in Sittler's program. Since the electrons are hot in this region, we are confident of the results. In the time periods from 1989-08-24T22:46:35.334 (236.94902) to 1989-08-24T23:32:12.481 (236.98070) and from 1989-08-25T08:09:47.233 (237.34013) to 1989-08-25T09:23:24.001 (237.39125), when the spacecraft is in hot plasma regions, all the electron parameters are derived from fits to the electron spectra. Again, we are confident of the results. In the regions where a cold electron component is present in the spectra (1989-08-24T23:35:23.424 (236.98291) to 1989-08-25T00:35:23.712 (237.02458) and from 1989-08-25T04:33:48.095 (237.19014) to 1989-08-25T08:02:35.233 (237.33513), the spacecraft is negatively charged and the density calculation is seriously affected by spacecraft charging. The total ion density from the PLS ion measurements and the condition of charge neutrality are used to estimate the spacecraft potential. The true density of each electron component is equal to d0*exp(-Vsc/T), where d0 is the density from the fits assuming a zero spacecraft potential, Vsc is the spacecraft potential and T is the temperature of that component. Uncertainties in the electron density should thus mainly determined by the ion density calculation. However, electron temperature calculations are not affected by the spacecraft charging, so they are quite accurate. In the time period from 1989-08-25T00:45:47.520 (237.03180) to 1989-08-25T02:42:02.592 (237.11253), the cold component is below the threshold the PLS measurement. A temperature of 3 eV is assumed for the cold component. The spacecraft potential is not available, so is set equal to zero. The parameters of the hot electron components are obtained directly from the fits. The cold electron density is then set equal to the total ion density minus the hot electron density. In this region the results have large error bars. In the region near closest approach (1989-08-25T04:11:23.712 (237.17458) to 1989-08-25T04:25:34.752 (237.18443), where the loss-cone effect is prominent, the density of each component is equal to d0*ditot/detot, where d0 is the density of the component calculated from the fits, ditot is the total ion density, detot is the total electron density from the fits. Table 1 contains hourly summaries of the percentage of the data available, data quality, and contamination codes. Tables 2 and 3 contain descriptions of the data quality and data contamination ID's respectively. ------------------------------------------------------------------- Table 1. Hourly Data Coverage and Quality Summaries ------------------------------------------------------------------- Start Time Mode Percent Qual Contam NumGood ------------------------------------------------------------------- 1989-08-24T15:00:54 E1/E2 35.135 -1 -1 182 1989-08-24T16:00:29 E1/E2 129.730 -1 -1 672 1989-08-24T17:09:40 E1/E2 81.081 -1 -1 420 1989-08-24T18:00:29 E1/E2 72.973 -1 -1 378 1989-08-24T19:00:29 E1/E2 94.595 -1 -1 490 1989-08-24T22:46:35 E1/E2 37.838 -1 -1 196 1989-08-24T23:01:00 E1/E2 16.216 -1 -1 84 1989-08-25T00:00:59 E1/E2 81.081 -1 -1 420 1989-08-25T01:09:48 E1/E2 51.351 -1 -1 266 1989-08-25T02:06:03 E1/E2 43.243 -1 -1 224 1989-08-25T04:11:23 E1/E2 21.622 -1 -1 112 1989-08-25T05:01:00 E1/E2 56.757 -1 -1 294 1989-08-25T06:00:59 E1/E2 78.378 -1 -1 406 1989-08-25T07:00:59 E1/E2 45.946 -1 -1 238 1989-08-25T08:01:00 E1/E2 54.054 -1 -1 280 1989-08-25T09:00:59 E1/E2 51.351 -1 -1 266 1989-08-25T09:23:24 E1/E2 16.216 -1 -1 84 -------------------------------------------------------------------- Table 2. Data Quality ID Descriptions -------------------------------------------------------------------- ID Description -------------------------------------------------------------------- -1 no attempt has been made to specify a data quality for this time range -------------------------------------------------------------------- Table 3. Data Contamination ID Descriptions -------------------------------------------------------------------- ID Description -------------------------------------------------------------------- -1 no evaluation of possible contamination has been made