Robert E. Daniell

Transport-theoretic model for the electron-proton-hydrogen atom aurora: 1. Theory

The first self-consistent transport-theoretic model for the combined electron-proton-hydrogen atom aurora is presented. This is needed for accurate modeling of the diffuse aurora, particularly in the midnight sector, for which a statistical study (Hardy et al., 1989) indicates that the proton contribution to the total auroral energy flux is (on the average) about 20 to 25% of that of the electrons. As a result, the ionization yield as well as the yields of many emission features will be underestimated (on the average) by about the same percentage if the proton-hydrogen atom contributions are neglected. The model presented here can also be used to study a pure electron aurora or a pure proton-hydrogen atom aurora by choosing the appropriate boundary conditions, namely, by setting the incident flux of one or the other particle population equal to zero. In the latter case, the new feature of the present model is the rigorous transport-theoretic treatment of the contributions to ionization rates and to emission rates and yields from the secondary electrons produced by protons and hydrogen atoms. A coupled set of three linear transport equations is presented. Protons and hydrogen atoms are coupled only to each other through charge-changing (charge exchange and stripping) collisions, while the electrons are coupled to both protons and hydrogen atoms through the secondary electrons that they produce. Source functions for the secondary electrons produced by the three primary particle populations are compared and contrasted, and the numerical methods for solving the coupled transport equations are described. Finally, formulas for calculating pertinent aurora-related quantities from the particle fluxes are given. In the companion paper (Strickland et al., this issue), the model results are presented.

Negative ionospheric storm coincident with DE 1‐observed thermospheric disturbance on October 14, 1981

The DE 1 far ultraviolet (FUV) imaging instrument recorded a large thermospheric disturbance over Europe and Russia on October 14, 1981, during a geomagnetic storm commencing near the end of the previous day. The disturbance is quantified in terms of O/N2, the column density ratio referenced to a fixed depth in N2. The ratio is derived from DE 1 dayglow observations with a filter whose signal transmission is dominated by O I 130.4-nm emission. Within the disturbed region, O/N2 is less than that in surrounding regions, with minimum values being more than a factor of 2 smaller than undisturbed values. Images of O/N2 are compared to ground-based ionosonde data from 13 sites, some within and others outside of the disturbed region. The data are in the form of Nmax, the maximum electron density, which in the presence of an F2 layer is equivalent to NmF2. The data exhibit negative ionospheric storm effects (reduced Nmax) within the disturbed region and normal behavior elsewhere. The degree of correlation between O/N2 and Nmax suggests that the approximate geographical extent of dayside regions experiencing negative ionospheric storm effects can be determined from global FUV imaging of the disturbed and surrounding regions. The analysis is extended to the following day to address the recovery of the disturbed region. The O/N2 ratio has returned to undisturbed values except in a smaller disturbance region containing weak reductions in O/N2. This is either a remnant of the strong disturbance from the day before or a newly formed disturbance from substorm activity several hours prior to the new observations. Only the ionosonde sites within this region recorded values of Nmax below their monthly median values.

Six days of thermospheric‐ionospheric weather over the Northern Hemisphere in late September 1981

Thermospheric and ionospheric behavior over a 6-day period beginning on September 24, 1981 (day 267), is discussed using DE 1 far ultraviolet dayglow data and ground-based ionosonde data. The DE 1 data are processed to produce images of O/N2, the column density of O relative to N2. Ionospheric data are in the form of Nmax, the maximum electron density that is equivalent to NmF2 provided an F2 layer is present. Day-to-day variations in these parameters and their relationship to one another are examined in three geographical regions: Siberia/Japan, Europe, and North America. The 6-day period begins and ends with undisturbed days and includes a 2-day geomagnetic storm period with onset on day 269. Several disturbances in the form of reduced O/N2 are observed, with the most severe occurring during the storm. For those ionosonde sites located within the disturbed regions, negative ionospheric effects are observed similar to those reported by Strickland et al. [2001] for a different storm period. In Siberia, 4 consecutive days of negative effects are observed that coincide with reductions in O/N2. Middle- to low-latitude enhancements in O/N2 are also observed that are more global and less structured than regions of reduced O/N2. Percentage changes in the enhancement from quiet time values are typically less than ∼20% in contrast to much larger changes in well-developed regions of reduced O/N2. Several instances of positive ionospheric effects are observed that are in phase with coincident O/N2 enhancements, but the coupling is less convincing than that between negative ionospheric effects and O/N2 reductions. It is, nevertheless, seen often enough in this work to argue that compositional effects in addition to dynamical effects must be considered in addressing the causes of long-duration positive ionospheric storm behavior.

Modeling negative ionospheric storm effects caused by thermospheric disturbances observed in satellite UV images

The ionospheric behavior over Podkamennaya, Russia, during the geomagnetic storm of October 14, 1981, is modeled subject to the constraints provided by ƒoF2 measurements and by the thermospheric O/N2 ratio deduced from a DE 1 FUV image taken at 0540 UT. The (nonunique) diurnal variation of O/N2 deduced from the model is consistent with the thermospheric composition disturbance zone observed in the DE 1 image having moved over Podkamennaya during the early morning hours, producing a reduction of O/N2 (referred to a column density of N2 of 1017 cm−2) to a value of less than 0.2 before recovering to a value of 0.6 during the afternoon hours. Although the data are insufficient to provide a unique solution, the results demonstrate the utility of satellite-based FUV images in the study of thermospheric and ionospheric disturbances produced by geomagnetic storms.

Determination of Ionospheric Electron Density Profiles From Satellite UV Emission Measurements

This paper addresses the problem of using satellite ultraviolet measurements to deduce the ionospheric electron density profile (EDP). The ionospheric processes that produce the ultraviolet emissions differ from region to region, so it is necessary to consider separate approaches for the various ionospheric subregions. We will discuss approaches suitable for (1) the midlatitude daytime ionosphere, (2) the midlatitude nighttime ionosphere, and (3) the undisturbed auroral E-layer.

AURIC airglow modules - Phase 1 development and application

The Atmospheric Ultraviolet Radiance Integrated Codes modules have been developed to calculate the 1000-6500 A thermospheric emission spectra and radiances of dayglow, nightglow, twilight, and electron aurora, while also accounting for solar, photoelectron, auroral electron, and chemical excitation processes as well as pure and self absorption and multiple scattering effects. An account is presently given of the overal architecture of the codes; attention is given to the design and implementation of the photoionization and electron flux modules, together with samples of the input data and generated output.