A calculation of symmetric resonant charge exchange cross sections has been made for a selection of atoms in the velocity range where the impact parameter method is applicable. Cross sections for other atoms can be estimated by interpolating in terms of their ionization potentials. The results are in fair agreement with experiment. A similar calculation has been attempted for asymmetric nonresonant charge exchange processes. The approximations used are more restrictive in this calculation, the calculations being only semiquantitative in nature. The cross section of an asymmetric charge exchange process is determined in terms of the ΔE of the reaction and the ``average'' ionization potential of the two atoms. The results are qualitatively in agreement with experiment. A very brief discussion of approaches for extrapolating data to lower velocities, where the rectilinear orbit impact parameter method is not applicable, is given.

Adopting the view that the sudden commencement of a geomagnetic storm (SC) is the result of the impact on the geomagnetic field of an abrupt solar-plasma front, the form of the SC observed on the surface of the earth is investigated. A model is constructed to represent the shape of the geomagnetic field boundary as perturbed by the solar plasma. Calculations (carried out in the equatorial plane for simplicity) show that, regardless of how abrupt may be the impact of a solar-plasma front on the geomagnetic field, the variation in hydromagnetic transit times from different positions on the boundary, down to a point on the surface of the earth, yields SC rise times of several minutes at ground level. These times are in agreement with the observed SC rise times. 2715

The transport of O+ ions from the cusp/cleft ionosphere to the magnetotail during highly disturbed times was determined by computing the guiding‐center trajectories of the ions to a distance of 6 RE from the ionosphere and the full‐motion trajectories at later times. Case histories were tallied in six planes perpendicular to the XGSM axis, three planes perpendicular to the YGSM axis, and in the center plane of the tail. At various times relative to the enhancement of the convection electric field, the following ion properties were constructed from the case histories: number density, mean energy, energy and pitch angle distributions of the flux, and ion pressure components parallel and perpendicular to the magnetic field. It was found that after about 1.7 hours the ion flux in the near‐Earth magnetotail increased dramatically and the spectrum hardened, much as observed during periods just preceding substorms. This increase is attributed to (1) the increase in the O+ outflux from the ionosphere, (2) the increased energization of the ions by the convection electric field, and (3) ion trapping, which generally occurs because the ion magnetic moments generally increase after the ions first cross the geomagnetotail center plane. Moreover, the parallel pressure of the ions exceeds the energy density of the magnetic field at XGSM < −8 RE. On the basis of the expected alterations of the magnetic and electric fields in response to this O+ pressure, a substorm trigger mechanism is suggested.

The transport of ions from the polar ionosphere to the inner magnetosphere during storm time conditions has been computed using a Monte Carlo diffusion code. The effect of the electrostatic turbulence assumed to be present during the substorm expansion phase was simulated by a process that accelerated the ions stochastically perpendicular to the magnetic field with a diffusion coefficient proportional to the rate of energization of the ions by the induced electric field. This diffusion process was continued as the ions were convected from the plasma sheet boundary layer to the double-spiral injection boundary. Inward of the injection boundary the ions were convected adiabatically. By using as input an O + flux of 2.8 x 108 cm -2 s -1 (w>10 eV) and an H + flux of 5.5 x 108 cm -2 s -1 (w>.63 eV) the computed distribution functions of the ions in the ring current were found to be in good agreement, over a wide range in L (4-8), with measurements made with the ISEE 1 satellite during a storm. This O + flux and a large part of the H + flux appear to be consistent with the DE-1 and DE-2 satellite measurements of the polar ionospheric outflow during disturbed times.

A numerical integration of the hydromagnetic wave equations in the ionosphere has been carried out. Tables and graphs are given for the relations between the field amplitudes above and below the ionosphere and for the power dissipated as a function of altitude. The case of a vertically incident plane monochromatic wave near 45 ø geomagnetic latitude is treated. The results are used to confirm earlier estimates of ionospheric heating by hydromagnetic waves and to estimate the transit time of extremely low-frequency signals.