John Jasperse

Upgoing electrons produced in an electron-proton-hydrogen atom aurora

The first test of a self-consistent theory for the combined electron-proton-hydrogen (H) atom aurora is presented. Specifically, the upgoing differential electron flux that results from precipitating protons and electrons is modeled and compared to observations. The observations are from the Low Altitude Plasma Instrument (LAPI) on board the Dynamics Explorer 2 satellite. Excellent agreement between data and theory is produced when a kappa distribution is used to extrapolate the observed proton spectra to energies beyond the instruments energy cutoff (27 keV). More definitive tests of the model will require more comprehensive observations as well as improvements in available proton-H atom cross sections. However, it is concluded that data clearly supports the theoretical prediction that the secondary electron spectra due to precipitating protons and H atoms is much softer than that produced by precipitating electrons. Also, the implication that the incoming proton spectra have a high-energy power law tail raises the possibility that previous determinations of the total ion energy flux are too low.

Proton transport model: A review

The linear transport model for the proton aurora developed at the Air Force Research Laboratory is reviewed. Emphasis is given on the discussion of the studies where the predictions of the model were compared with those of other theoretical methods and with the available data. The excellent agreement between the linear transport model and other theoretical methods gives credence to the accuracy of the numerical technique adopted in solving the transport equations, while good to excellent agreements between theory and observations indicate that the transport model adequately describes the important physics issues of the problem. It is concluded here that our ability to accurately model the proton aurora is limited only by the uncertainties in the input cross-section data (for some collision processes) and by our inadequate information about the incident proton spectra. Some discussions in this regard are included.

Effects of thruster firings on the shuttle's plasma and electric field environment

Simultaneous plasma and AC/DC electric field measurements taken during the space shuttle mission STS-4 at times of prolonged thruster firings are analyzed and cross correlated. Depending on the orientation of the shuttles velocity vector to the magnetic field, ion densities and electric field wave spectra were enhanced or decreased. The systematic picture of interactions within the shuttles plasma/neutral gas environment of Cairns and Gurnett (1991b) is confirmed and extended. Waves are excited by outgassed and thruster-ejected molecules that ionize in close proximity to the shuttle. On time scales significantly less than an ion gyroperiod, the newly created ions act as beams in the background plasma. These beams are sources of VLF waves that propagate near the shuttle and intensify during thruster firings. Plasma density depletions and/or the shuttles geometry may hinder wave detection in the payload bay. A modified two-stream analysis indicates that beam components propagating at large angles to the magnetic field are unstable to the growth of lower hybrid waves. The beam-excited, lower hybrid waves heat some electrons to sufficient energies to produce impact ionization. Empirical evidence for other wave-growth mechanisms outside the lower-hybrid band is presented.

Transport theoretic solutions for the beam-spreading effect in the proton-hydrogen aurora

In this paper, we give matched asymptotic solutions for the particle fluxes in the Earths proton-hydrogen aurora. The proton (ΦP) and hydrogen atom (ΦH) fluxes are functions of two spatial and three velocity variables. These results are new and are given in closed form to the lowest order in the expansion parameter, which is the ratio of the proton gyroradius to the atmospheric scale height, and show a pronounced lateral, beam-spreading effect. Numerical calculations for ΦP and ΦH where no approximations are made are also given and found to agree reasonably well with the matched asymptotic solutions.

Determination Of Daytime Midlatitude Electron Density Profiles From Satellite UV And In-Situ Data

This paper addresses the problem of determining accurate, real-time ionospheric electron density profiles (EDP) using passive UV and other sensor measurements from satellites. This is done by using real-time satellite data to constrain the geophysical parameters that appear in an ab initio theoretical daytime midlatitude ionospheric model, creating what we call the AFGL constrained EDP model. In February and March 1987 a series of coincident measurements were made by the Millstone Hill incoherent scatter radar and the Polar BEAR satellite multispectral UV imager. These observations of electron density profiles and daytime UV airglow give us an excellent opportunity to test the AFGL constrained EDP model with observational data. Using the satellite UV data and the radar-determined plasma data at one altitude (in-situ satellite plasma measurements were not available), we apply the constrained AFGL model to compute the EDP from about 90 to 600 km. By comparing the model results to the EDP measured by the radar, we show that the AFGL constrained EDP model predicts the EDP more accurately than can empirical models, such as the International Reference Ionosphere (IRI), which contain no real-time data.