Ionospheric TEC periodic perturbations associated with MSTIDs and ionosonde data during the 2020/2021 SSW

The vertical total electron content (vTEC) was calculated from dual-frequency GNSS measurements with a sampling rate of 30 seconds. The detrended TEC perturbation (dTEC) is extracted by applying a band-pass filter with a cutoff window of 10–60 minutes to the raw vTEC series, effectively extracting the MSTID-scale components from the background trends. Some studies also use the ratio of TEC perturbation values to background values as an indicator of MSTID activity, in order to eliminate the influence of background TEC. To quantitatively assess the disturbance intensity associated with MSTIDs in a given region, we employ both absolute and relative perturbation indices, achieved by calculating the absolute values of amplitude perturbations (|dTEC| and |dTEC/TEC|, respectively) (dTEC and rdTEC in this dataset) and averaging within spatiotemporal grid cells of 1° ×1°×15 min. The critical frequency of the sporadic E layer (foEs) and the occurrence of spread-F were obtained from the ionosonde at Lanzhou station (36°N,104°E) from the China Research Institute of Radio-wave Propagation (CRIRP)