Peter M. Banks

Dynamical behavior of thermal protons in the mid-latitude ionosphere and magnetosphere

Abstract Satellite and other observations have shown that H+ densities in the mid-latitude topside ionosphere are greatly reduced during magnetic storms when the plasmapause and magnetic field convection move to relatively low L-values. In the recovery phase of the magnetic storm the convection region moves to higher L-values and replenishment of H+ in the empty magnetospheric field tubes begins. The upwards flow of H+, which arises from O+—H charge exchange, is initially supersonic. However, as the field tubes fill with plasma, a shock front moves downwards towards the ionosphere, eventually converting the upwards flow to subsonic speeds. The duration of this supersonic recovery depends strongly on the volume of the field tube; for example calculations indicate that for L = 5 the time is approximately 22 hours. The subsonic flow continues until diffusive equilibrium is reached or a new magnetic storm begins. Calculations of the density and flux profiles expected during the subsonic phase of the recovery show that diffusive equilibrium is still not reached after an elapsed time of 10 days and correspondingly there is still a net loss of plasma from the ionosphere to the magnetosphere at that time. This slow recovery of the H+ density and flux patterns, following magnetic storms, indicates that the mid-latitude topside ionosphere may be in a continual dynamic state if the storms occur sufficiently often.

Observations of joule and particle heating in the auroral zone

Abstract Observational data from the Chatanika, Alaska incoherent scatter radar have been used to deduce atmospheric heating rates associated with particle precipitation and joule dissipation. During periods when Chatanika is in the vicinity of the auroral oval the height-integrated heat input to the lower thermosphere can be as large as 100 ergs cm −2 sec −1 with joule and particle heating rates of comparable magnitude. Altitude profiles of these heat inputs are also obtained, showing that the energy liberated by joule dissipation tends to peak at a substantially higher altitude (~130 km) than that due to particles (100–120 km). As a consequence, it follows that joule heating can be expected to provide a rapid means for creating thermospheric disturbances. It is also pointed out that joule and particle heating are permanent features of the auroral oval and polar cap. As such, expansion of the auroral oval leads to an increase in the total global heating and, hence, to the close relationship between magnetic disturbances and thermospheric perturbation.

A comparison of the temperature and density structure in high and low speed thermal proton flows

Abstract The continuity, momentum and energy hydrodynamic equations for an H + -O + topside ionosphere have been solved self-consistently for steady state conditions similar to those found outside the plasmasphere. Results are given for undisturbed and trough conditions with a range of H + outflow velocities yielding subsonic and supersonic flow. In the formulation of the equations, account was taken of the velocity dependence of ion-neutral, ion-ion and ion-electron collision frequencies. In addition, parallel stress and the nonlinear acceleration term were retained in the H + momentum equation. Results computed from this model show that, as a result of Joule (frictional) heating, the H + temperature rises with increasing outflow velocity in the subsonic flow regime, reaching a maximum value of about 4000 K. For supersonic flow other terms in the H + momentum equation become important and alter the H + velocity profile such that convection becomes a heat sink in the 1000–1500 km altitude range. This, together with the reduced Joule heating resulting from the high-speed velocity dependence of the H + collision frequencies, results in a decrease in the H + temperature as the outflow velocity increases. However, for all outward flows the H + temperature remains substantially greater than the O + temperature. With identical upper boundary velocities, the H + flow velocity is higher at low altitudes for trough conditions compared with non-trough conditions, but the H + temperature in the trough is lower. The form of the H + density profiles for supersonic flow does not in general differ greatly from those obtained with wholly subsonic flow conditions.

A review of auroral zone electrodynamics deduced from incoherent scatter radar observations

Abstract A review is given of recent incoherent scatter radar measurements of auroral zone electric fields, conductivities and E -region currents as observed at Chatanika, Alaska. Discussion is given of the diurnal variation of the local electric field in a variety of quiet and disturbed conditions. These results emphasize the close connection between ionospheric measurements and magnetospherio processes. E -region currents inferred from the radar data are also presented and discussed with respect to agreement with surface magnetograms.

The influence of convection electric fields on thermal proton outflow from the ionosphere

Abstract The continuity, momentum and energy hydrodynamic equations for an O + -H + ionosphere have been solved self-consistently for steady state conditions when a perpendicular (convection) electric field is present. Comparison of the H + temperature profiles obtained with and without the electric field show that the effect of the electric field is to enhance the H + temperature at high altitudes from about 3600 to 6400 K. Due to ion heating by the electric field, there is a net reduction of O + in the F 2-region as compared with the case of a non-convecting ionosphere. When the reduction of O + is neglected, the electric field acts to increase the H + outward flux from 8.3 × 10 7 to 2.7 × 10 8 cm −2 sec −1 for average ionospheric conditions. However, when the reduction of O + is included, there is a net reduction in the outward H + flux. Nevertheless, the convection electric field still results in an increase in the rate of depletion of the F -re m −1 electric field.

The temperature coupling of ions in the ionosphere

Abstract An investigation has been made of the extent to which 0+, He+, and H+ ions can be considered as having a common temperature in the ionosphere. By assuming that each ion gas has its own Maxwellian velocity distribution, energy balance equations including the effects of heating by the electron gas, cooling by the neutral atmosphere, and energy coupling between the ion species have been obtained. Solutions to the energy equations for three models of the neutral atmosphere indicate that the H+ and He+ ion temperatures are higher than the 0+ temperature in the regions between 250 and 650 km. A peak temperature difference greater than 200° occurs for H+ and 0+ ions, while values which may reach 100° are noted for the He+−O+ separation. An explanation of the temperature inequality has been made in terms of the atmospheric and ionospheric conditions, showing that the altitude extent of ion temperature separation increases for rising thermospheric and electron temperatures and decreases for progressively larger electron densities.

The thermal structure of the ionosphere

From a large number of rocket, satellite, and ground-based experiments since 1959 it is known that the electron and ion gases of the middle and upper ionosphere are substantially hotter than the neutral atmosphere. At low and midgeomagnetic latitudes the principal heating agent for the ionospheric plasma lies in the excess kinetic energy given to photoelectrons arising from the ionization of the atmospheric gases by solar ultraviolet radiation. Although the photoelectrons lose most of their kinetic energy in the excitation of atomic and molecular gases, a significant amount of energy is given to the ambient Maxwellian electron gas, increasing its temperature above that of the neutral gases. The ion gases, in contrast, appear to be heated almost entirely through the elastic collisions with ambient electrons so that the ion temperature generally lies between the electron and neutral temperatures. The calculation of theoretical temperature profiles has developed into a moderately sophisticated process with a fair degree of correspondence between predicted and observed values for undisturbed geophysical conditions. Current research emphasizes the global aspects of plasma temperatures and the connection between ionospheric and magnetospheric phenomena. However, many of the observed diurnal and seasonal variations in both electron and ion temperatures depend upon the couplings between the neutral and ionized atmospheres, and a complete understanding of all aspects of the ionospheric thermal balance is not possible at the present time.

Accidentally resonant charge exchange and ion momentum transfer.

Ion momentum transfer through charge exchange in mixture of ion gases and parent neutral gases under thermal nonequilibrium, noting role of Boltzmann equation

Charge exchange and ion diffusion for thermal nonequilibrium conditions

The ion-neutral diffusion coefficient for resonance charge exchange has been obtained directly from Boltzmanns equation for conditions of separate ion and neutral Maxwellian gas temperatures. With application to the problems of O+−O and H+−H diffusion it is found that there is little effect upon the F2-region maximum since Ti

Hydrogen ion velocity distributions in the ionosphere

Tn. At higher altitudes, where T >Tn to a significant degree, the present diffusion coefficient becomes substantially larger than previous expressions based upon a condition of thermal equilibrium between ion and neutral gases.