5:15 PM - 6:45 PM
[PEM12-P18] Statistical analysis of medium-scale traveling ionospheric disturbances over South Africa based on GNSS observations
Keywords:Medium-Scale Traveling Ionospheric Disturbances (MSTIDs), Global Navigation Satellite System (GNSS) receiver network, Total Electron Content (TEC), Atmospheric Gravity Waves (AGWs), Sporadic E (Es layer), Perkins Instability
Medium-scale traveling ionospheric disturbances (MSTIDs), which are temporal and spatial perturbations of the electron density in the F-region, can cause measurement errors in precise satellite positioning. This phenomenon can be observed by 2-dimensional maps of data obtained from the fluctuation components of the total electron content (TEC) between the satellite and receiver. So far, this type of observation has been conducted in areas where many Global Navigation Satellite System (GNSS) receivers are installed, such as Japan and Europe. In this study, we attempted the first observation using this method in South Africa, where GNSS receivers have recently been installed, and analyzed statistically the occurrence rate and propagation direction of MSTIDs in 2022.
By analyzing two-dimensional maps of detrended TEC obtained from subtracting 1-hour running average from the original TEC for a pair of satellite and receiver, we investigate seasonal and local time variations in the occurrence rate and propagation direction of MSTIDs over South Africa. The statistical data on the occurrence rate showed a primary peak during the daytime and a secondary peak during the nighttime around the June solstice, and a low occurrence rate at dawn and dusk on the December solstice. The statistical data on the propagation direction showed that the MSTID propagation is mainly to the northeast during the daytime and mainly to the west during the nighttime, regardless of the season. These results suggest that the generation mechanism of MSTIDs differs between daytime and nighttime, and that seasonal variations exist in each generation mechanism.
Daytime MSTIDs occur highly around the June solstice and propagate mainly in the equatorial direction, suggesting that atmospheric gravity waves (AGWs) are likely to be the cause of the MSTIDs, as reported by previous studies. On the other hand, the propagation direction of nighttime MSTIDs show westward preference. Considering the westward declination of geomagnetic field over South Africa, the nighttime MSTIDs over South Africa are likely to be generated through the Perkins instability and E and F region electrodynamical coupling, as has been thought so far. However, the occurrence rate of nighttime MSTIDs over South Africa is lower than in other regions.
In this study, the obtained statistical results are compared with those of previous studies, and the statistic characteristics of MSTIDs observed over South Africa were summarized. We discuss possible causes for each of the similarity and difference observed. In this presentation, we will mainly discuss the nighttime MSTIDs, which show a different tendency in other regions.
By analyzing two-dimensional maps of detrended TEC obtained from subtracting 1-hour running average from the original TEC for a pair of satellite and receiver, we investigate seasonal and local time variations in the occurrence rate and propagation direction of MSTIDs over South Africa. The statistical data on the occurrence rate showed a primary peak during the daytime and a secondary peak during the nighttime around the June solstice, and a low occurrence rate at dawn and dusk on the December solstice. The statistical data on the propagation direction showed that the MSTID propagation is mainly to the northeast during the daytime and mainly to the west during the nighttime, regardless of the season. These results suggest that the generation mechanism of MSTIDs differs between daytime and nighttime, and that seasonal variations exist in each generation mechanism.
Daytime MSTIDs occur highly around the June solstice and propagate mainly in the equatorial direction, suggesting that atmospheric gravity waves (AGWs) are likely to be the cause of the MSTIDs, as reported by previous studies. On the other hand, the propagation direction of nighttime MSTIDs show westward preference. Considering the westward declination of geomagnetic field over South Africa, the nighttime MSTIDs over South Africa are likely to be generated through the Perkins instability and E and F region electrodynamical coupling, as has been thought so far. However, the occurrence rate of nighttime MSTIDs over South Africa is lower than in other regions.
In this study, the obtained statistical results are compared with those of previous studies, and the statistic characteristics of MSTIDs observed over South Africa were summarized. We discuss possible causes for each of the similarity and difference observed. In this presentation, we will mainly discuss the nighttime MSTIDs, which show a different tendency in other regions.