Latitudinal and temporal variation of equatorial ionospheric irregularities determined from GPS scintillation observations

In this paper we investigate the spatial and tempo- ral 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 re- gional network of GPS based scintillation monitors (Thomas et al., 2001). The aim of this analysis is to better understand the mor- phology 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 scin- tillation 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 implica- tions for models which rely on phase screen diffraction the- ory.