The Defence Science and Technology Organisation (DSTO) has initiated an experimental program, Spatial Ionospheric Correlation Experiment, utilizing state‐of‐the‐art DSTO‐designed high frequency digital receivers. This program seeks to understand ionospheric disturbances at scales < 150 km and temporal resolutions under 1 min through the simultaneous observation and recording of multiple quasi‐vertical ionograms (QVI) with closely spaced ionospheric control points. A detailed description of and results from the first campaign conducted in February 2008 were presented by Harris et al. (2012). In this paper we employ a 3‐D magnetoionic Hamiltonian ray tracing engine, developed by DSTO, to (1) model the various disturbance features observed on both the O and X polarization modes in our QVI data and (2) understand how they are produced. The ionospheric disturbances which produce the observed features were modeled by perturbing the ionosphere with atmospheric gravity waves.

In this paper we investigate the spatial and temporal distribution of ionospheric irregularities in the South-East Asian longitude sector by analysing the scintillation of GPS signals received at ground based stations. The data used for this work were collected during 1998 to 2002 with our regional network of GPS based scintillation monitors (Thomas et al., 2001). The aim of this analysis is to better understand the morphology and climatology of ionospheric irregularities in our region. Interesting differences between the north and south anomalies are noted when we examine the latitudinal–temporal variation of irregularity activity. We investigate the possible causes of these differences and note that variations in the irregularity seeding mechanism and in the background ionosphere at the two anomalies could be important. Phase screen diffraction theory is used to analyse our scintillation data and we note problems with this theory for ray-paths with large off-zenith angles. The height of the phase screen is another important issue. We discuss the implications for models which rely on phase screen diffraction theory.

The strength of high‐frequency radio signals, when refracted by the ionosphere, can be strongly influenced by ionospheric absorption. Accurate modeling of the amount of this absorption is a vital part of many studies of radio waves propagating in the ionosphere. We have developed a new, flexible model of ionospheric absorption, the Semiempirical Model for Ionospheric Absorption based on the NRLMSISE‐00 atmospheric model (SiMIAN). This article describes the methods and formulae used by SiMIAN, a comparison of SiMIAN with an older absorption model, and validation work performed by simulating the power returned in vertical incidence soundings of the ionosphere and comparing the results with real soundings.