[1] The problem of electron density inversion of digital ionograms is reconsidered from the viewpoints of new possibilities and of modern requirements. The data processing system of an advanced ionosonde (the dynasonde) provides accurate measurements not only of echo group range but also of direction of arrival, among other physical parameters, thus yielding the three-dimensional distribution of apparent echolocations in each ionogram recording. An iterative ray-tracing approach is described here to recover the parameters of a quite sophisticated three-dimensional (so-called wedge-stratified ionosphere) model of the local electron density distribution, characterizing its actual vertical N e (h) profile together with horizontal gradients and general tilts. The power of a contemporary PC is sufficient to accomplish this analysis quickly. This approach is implemented in the algorithm introduced here, is named ''NeXtYZ,'' and is pronounced ''next wise.'' Citation: Zabotin, N. A., J. W. Wright, and G. A. Zhbankov (2006), NeXtYZ: Three-dimensional electron density inversion for dynasonde ionograms, Radio Sci., 41, RS6S32,

Ambient noise in the ocean provides acoustic illumination, which can be used, similarly to daylight in the atmosphere, to visualize objects and characterize the environment. It has been shown theoretically that deterministic travel times between any two points in a moving or motionless, inhomogeneous, time‐independent medium can be retrieved from the cross‐correlation function of diffuse acoustic noise recorded at the two points, without a detailed knowledge of the noise field's sources or properties. In this paper, techniques are developed to account for receiver motion and suppress contributions due to powerful transient localized noise sources, such as nearby shipping, in order to enhance noise diffusivity. The data‐processing techniques are applied to ambient noise recordings of opportunity, which were obtained as a by‐product of a long‐range sound propagation experiment in the Pacific Ocean. The feasibility of passive ocean acoustic tomography with ambient noise recorded at two vertical line arrays is demonstrated successfully.

Recently reported lidar observations have revealed a persistent wave activity in the Antarctic middle and upper atmosphere that has no counterpart in observations at midlatitude and low‐latitude locations. The unusual wave activity suggests a geographically specific source of atmospheric waves with periods of 3–10 h. Here we investigate theoretically the hypothesis that the unusual atmospheric wave activity in Antarctica is generated by the fundamental and low‐order modes of vibrations of the Ross Ice Shelf (RIS). Simple models are developed to describe basic physical properties of resonant vibrations of large ice shelves and their coupling to the atmosphere. Dispersion relation of the long surface waves, which propagate in the floating ice sheet and are responsible for its low‐order resonances, is found to be similar to the dispersion relation of infragravity waves in the ice‐free ocean. The phase speed of the surface waves and the resonant frequencies determine the periods and wave vectors of atmospheric waves that are generated by the RIS resonant oscillations. The altitude‐dependent vertical wavelengths and the periods of the acoustic‐gravity waves in the atmosphere are shown to be sensitive to the physical parameters of the RIS, which can be difficult to measure by other means. Predicted properties of the atmospheric waves prove to be in a remarkable agreement with the key features of the observed persistent wave activity.