Investigation of disturbances in ionosphere over Turkey using ionolab-fast fourier transform (I-FFT)

The ionosphere is a very important atmospheric layer for the satellite based systems and HF communication. Many forces such as solar magnetism, solar wind, magnetic activity of the earth and gravity act the variability in the temporal and spatial trends of the ionosphere. These forces generate some anomalies and disturbances in the form of wave -like oscillations, which propagate at a certain frequency, duration and velocity in the ionosphere. Total Electron Content (TEC) is one of the most important parameters in observing the structural variability of the ionosphere. Vertical Total Electron Content (VTEC) is the total number of electrons computed in the direction of local zenith of the receiver. In this study, the frequency and duration of wave-like oscillations are determined using a DFT (Discrete Fourier Transform) based algorithm over the VTEC values estimated from single GPS (Global Positioning System) stations. The method, namely IONOLAB-FFT is applied to VTEC data from Turkish National Permanent GPS Network (TNPGN Active) obtained for 2010, 2012 and 2012 to detect the frequency and duration of both medium and large scale TIDs (Traveling Ionospheric Disturbances). It is observed that the frequencies decrease from North to South and from West to East in Turkey. The frequencies decrease and the durations increase from solar active year 2012 to solar quiet year 2010. When the disturbed day and quiet day compare with each other, it is observed that frequencies in disturbed day are smaller than those in quiet day. It is observed that IONOLAB-FFT can estimate TIDs with more than 80% accuracy as such: frequencies from 0.21 mHz to 1.0 mHz and durations longer than 85 min; frequencies from 0.11 mHz to 0.39 mHz and durations longer than 157 min.