A study of ionospheric irregularities with spatial fluctuation of TEC

Abstract

Ionospheric irregularities are small-scale disturbances in the ionosphere which disrupt radio waves by causing amplitude and phase scintillations. Global Navigation Satellite System (GNSS) network can work as two-dimensional array to provide the spatial structure of the irregularities. With derived vertical total electron content (VTEC), we propose a spatial fluctuation of TEC (SFT) parameter to identify and analyze ionospheric irregularities. It is defined as the spatial dispersion of VTEC within a specific area at a given time. With the observations from the GNSS Earth Observation Network of Japan (GEONET), the size of the specific area for SFT calculation can be chosen as 0.8 ° × 0.8 ° in longitude and latitude, which corresponds to approximately 77 km × 95 km at 35°N at 400 km height. An SFT map is generated by sliding window at a step size of 0.1°, which shows the spatial structure of the ionospheric irregularities and hence gives the size, shape, orientation and intensity distribution of the irregularity structures. Evolution of ionospheric irregularities can be studied with SFT maps. Case studies are carried out for three strong irregularity events on February 12, 2000, March 20, 2001 and November 10, 2004. The irregularities are found to present as anisotropic branching structures, which elongate in north-south direction when first seen at lower latitudes. The structures can move and deviate from their previous orientations, and eventually drift perpendicular to their orientations. Such analyses with SFT should be interesting for morphology study and model construction of ionospheric irregularities.