An analysis of geomagnetic disturbances and global ionospheric electron density perturbations during the 2015 St. Patrick’s Day geomagnetic storm is presented in this paper. GPS observations from worldwide IGS stations are used and analysed through GPS-TEC analysis application developed by Gopi Seemala to get VTEC profiles. The St. Patrick’s geomagnetic storm covers the interval of 15-23 March 2015, when transient solar eruptions (a prolonged C9-class solar flare and associated CMEs on 15 March) and a strong geomagnetic storm during 16-18 March (Dst dropped to -223 nT) were reported. This geomagnetic storm led to complex effects on the ionosphere. The global maps have been created after analysing VTEC profiles at Low, Mid and High-latitudes over different longitudinal sectors. Major features of the positive and negative ionospheric storm development are observed in Asian, European and American Low, Mid and High-latitudes.

In this study, possible ionospheric precursors of the Mw7·1 Van earthquake are investigated with temporal, spatial and spectral analyses. For this purpose, Global Navigation Satellite System (GNSS) data of 11 International GNSS Service (IGS) stations and 17 Turkish National Permanent Real-Time Kinematic (RTK) Network (TNPGN-Active) stations were utilised. In addition, Global Ionosphere Map (GIM) data produced by the Center for Orbit Determination in Europe (CODE) was used to obtain GIM-vertical Total Electron Content (vTEC) values for the epicentre. The results of the temporal and spectral analysis indicate an increase (2–8 Total Electron Content Units (TECU)) before the Van earthquake occurred on 9 October, 15–16 October and 21–23 October within 15 days, 8–9 days and 1–3 days prior to the earthquake. The Cross-Wavelet Transform (CWT) method was used to examine the presence of correlation between noticeable variations and space-weather. It is deduced from the CWT analysis that the anomalies should originate from either solar effects or the Van earthquake due to coupling between the F10·7 solar activity index and TEC variations on the anomaly days. The results demonstrate that interdisciplinary approaches and various methods including frequency domain could be used to determine the presence of an earthquake-related anomaly in the ionosphere accurately.

Total electron content (TEC) measurements obtained at two Antarctic stations over nine months beginning early in 1994 have been analysed as a first step to performing ionospheric tomography. Two receiving systems were deployed at the Faraday and Halley research stations operated by the British Antarctic Survey to monitor signals from a random selection of passes of satellites in the Navy Navigational Satellite System. The resultant measurements of total electron content have been inverted and combined with ionosonde measurements of true height and foF2 to yield two-dimensional contour maps of ionospheric electron density. In spite of the poor geometry of the observations, some 130 satellite passes were found to be suitable for reconstruction using the techniques developed for ionospheric tomography. The contour maps of plasma density have been compared with independent observations of the vertical electron density profile measured by the dynasonde ionospheric sounder located at Halley. An example is presented of a deep trough investigated by the technique, illustrating the potential of the tomographic method for study of an extended spatial region of the ionosphere over inhospitable terrain.

Observations of satellite passes monitored at Halley and Terra Nova Bay have been combined to produce for the first time measurements of ionospheric electron content spanning the Antarctic continent. Results are presented from a sequence of four successive passes made during a period of some two hours that illustrate the development of the ionosphere over this wide spatial region. The observations are discussed in terms of the convective behaviour of the ionization, using results from the PACE radar and a standard model of the plasma flow.