First Comprehensive Study of MSTID Generation and Propagation Characteristics in Iran

Abstract

To investigate medium-scale TID (MSTIDs) at mid-latitudes across Iran, TEC data obtained from a dense ground-based GNSS receiver during the 7 months from May–November 2021 were analyzed. To remove the diurnal variability of the TEC, an 8th-order Butterworth bandpass filter was applied to the data. Then, two-dimensional TEC maps of the detrended TEC with a spatial resolution of 0.5$°\times$ 0.5$°$ in longitude and latitude were obtained. Considering MSTID periods, four bandpass filters were applied to the TEC data: 10–15, 15–20, 20–25, and 25–30 min. The objective was to determine whether MSTID propagation occurred during specific times and whether consistent directions were followed. The results indicate that MSTIDs in all bandpass filters exhibit the same direction at particular times. Distinctive MSTID features are revealed by lower period filters. To identify MSTID trends propagating throughout the region within each month, stations along a constant longitude were selected. The trends of each month were depicted using the Continuous Wavelet Transform (CWT) technique applied to the detrended TEC. The resulting 2D map illustrates MSTID occurrence trends based on the combination of day of the month and time of day. No nighttime trend, except for two cases in July, is observed. Most of the observed MSTID trends propagate southeastward. Notably, as the end of each month approaches, there is a time shift to earlier hours for MSTID activity. The horizontal phase velocity, wavelength, and amplitude of the trends fall within the range of 200–615 m/s, 152–460 km, and $\le 0.1$ dTECU, respectively.