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In this paper transient electromagnetic wave propagation in a stratified, anisotropic, dispersive medium is considered. Specifically, the direct scattering problem is addressed. The dispersive, anisotropic medium is modeled by constitutive relations (a 3 × 3 matrix-valued susceptibility operator) containing time convolution integrals. In the general case, nine different susceptibility kernels characterize the medium. An incident plane wave impinges obliquely on a finite slab consisting of a stratified anisotropic medium. The scattered fields are obtained as time convolutions of the incident field with the scattering kernels. The scattering (reflection and transmission) kernels are uniquely determined by the slab and are independent of the incident field. The scattering problem is solved by a wave splitting technique. Two different methods to determine the scattering kernels are presented; an imbedding and a Green functions approach. Explicit analytic expressions of the wave front are given for a special class of media. Some numerical examples illustrate the analysis.

High‐resolution Fabry‐Perot interferometric measurements of Doppler shift in the O+(²P°3/2 → ²D°5/2) emissions from daytime polar cusp auroras over Longyearbyen (Λ = 75°N), Svalbard, are presented to illustrate some temporal aspects of polar F region ion drifts. These measurements show some of the features expected of a pass under the throat region of a twin cell convection pattern. The dayside limits of the morning and evening convection cells can be discerned from the Doppler shift observations, but the expected strong poleward flow near local noon is not present. Ion convection velocities are found to vary from 100 to 800 ms−1. The interferogram contains profiles of the OH (8, 3) P1(2) rotational line at 7316.4 Å (completely resolved from the O+(²P°3/2 → ²D°5/2) 7320.2‐Å line), and the O+(²P°1/2 → ²D°5/2) 7319.4‐Å line which shows up on the short‐wavelength shoulder of O+(²P°3/2 → ²D°5/2) 7320.2‐Å line; all these lines appear in different orders. Most of the time the interferogram yields the 7320.2‐Å/7319.4‐Å intensity ratio value equal to the statistically weighted ratio of Å coefficients for the ²P1/2.3/2→ ²D5/2 transitions, though at times enhancement of the 7319.4‐Å line with respect to the 7320.2‐Å line is observed. The OH emission is generally weaker than the O+ 7320‐Å line, a result confirmed by simultaneous spectrophotometric observations which record maximum O+(²P) doublet intensities in the range of 20–230 R. Spectroscopic observations also confirm the absence of the N21P (5, 3) band or any other auroral emission in the cusp auroral spectra around 7320 Å, which may complicate interferometric studies of the ion line; the nearest OH rotational line is at 7316.4 Å. Additionally, the O+ 7320 Å doublet is at least an order of magnitude more intense than the OH 7316.4‐Å line in long‐rayed auroral forms occurring in the cusp region prior to and after local magnetic noon; during local magnetic noon the average energy of precipitating particles is much less than the energy of maximum ionization cross section for O. Temporal variations in the O+ 7320–7330‐Å emissions, observed with the spectrometer, indicate an effective lifetime of O+(²P) in the range 2.4±0.4 to 5±1 s; these time constants correspond to peak O+ emission heights above 200 km.

The dynamics of the upper thermosphere in the southern polar cap, auroral, and mid-latitude zones is reviewed. Information has been drawn from published measurements from the DE 2 and AE-C spacecraft and from ground-based stations and interpreted using the latest thermospheric general circulation models. Necessarily, frequent reference is made to the F region of the ionosphere, which permeates the upper thermosphere. Great emphasis is placed on the coupling and feedback mechanisms which exist between these interpenetrating fluids. It is shown that to obtain close approximation to observation, a complex model is required which incorporates these mechanisms in a self-consistent way. Published results from general circulation models show that there is a broad measure of agreement at both high and middle latitudes between simulation and observation over a wide range of geomagnetic activity for the sunlit southern middle and high latitudes near solar maximum. However, there are comparatively few data for a full investigation to be made, and present conclusions must be regarded as strictly interim. Strong driving forces in the auroral zones and polar caps cause a wind regime which is distinctly different from that observed at middle latitudes. Geomagnetic activity has been shown to have a strong effect on the extent of the high-latitude wind field, its strength, and its penetration to middle latitudes. The orientation of the interplanetary magnetic field has also been shown to be important. The coupling mechanisms between ions and neutrals heat the thermosphere and drive its circulation using energy from magnetospheric sources, but as yet the details of the thermosphere's variation with geomagnetic and solar activity are not clear from observations. The strong vertical winds reported in the literature are certainly indications of powerful heating, but the connection between observations of vertical winds and the production of gravity wave activity has not been established. Halley, Antarctica, is a critical station in the evaluation of model simulations of the winds in the upper thermosphere since it is a high-latitude station geographically but middle latitude geomagnetically and is subject to an unusual blend of driving forces. The observations are modeled surprisingly well considering the incomplete accounting of asynunetry caused by the large offset of the geomagnetic and geographic poles, and also of the South Atlantic anomaly. It is probable that, globally, there are detailed disagreements between Copyright 1988 by the American Geophysical Union. Paper number 8R0388. 8755-1209/88/008 R-0388515.00 the actual circulation and the simulations which have not yet come to light for the lack of observations. In the absence of new spacecraft experiments, new groundbased stations are required in the Antarctic region to enable simultaneous measurements to be made over a wide range of the southern polar cap. Introduction The thermosphere is generally of a mainly molecular composition at lower levels: molecular nitrogen and mo...

One-dimensional propagation of transient EM-waves in periodic media is studied. The media are periodic in the direction of propagation and can be of finite or infinite length. Wave propagators, that map a transient field from one point in the medium to another, are introduced. A number of useful relations for the propagators are presented. Some of these relations are used in the determination of explicit expressions for the short time behavior of a transient wave as it propagates in a periodic medium. The theory is exemplified by several numerical examples.