We analyze daytime quiet‐time MSTIDs between 2013 and 2015 at the geomagnetic equatorial and low latitude regions of the Chilean and Argentinian Andes using keograms of detrended total electron content (dTEC). The MSTIDs had a higher occurrence rate at geomagnetic equatorial latitudes in the June solstice (winter) and spring (SON). The propagation directions changed with the season: summer (DJF) [southeast, south, southwest, and west], winter (JJA) [north and northeast], and equinoxes [north, northeast, south, southwest, and west]. In addition, the MSTIDs at low latitudes observed between 8:00 and 12:00 UT occur more often during the December solstice and propagate northwestward and northeastward. After 12:00 UT, they are mostly observed in the equinoxes and June solstice. Their predominant propagation directions depend on the season: summer (all directions with a preference for northeastward), autumn (MAM) [north and northeast], winter (north and northeast), and spring (north, northeast, and southwest). The MSTID propagation direction at different latitudes was explained by the location of the possible sources. Besides, we calculated MSTIDs parameters at geomagnetic low latitudes over the Andes Mountains and compared them with those estimated at the geomagnetic equatorial latitudes. We found that the former is smaller on average than the latter. Also, our observations validate recent model results obtained during geomagnetically quiet‐time as well as daytime MSTIDs during winter over the south of South America. These results suggest that secondary or high‐order gravity waves (GWs) from orographic forcing are the most likely source of these MSTIDs.
A statistical picture of the occurrence and characteristics of Traveling Ionospheric Disturbances (TIDs) over the Antarctic Peninsula is established using Global Navigation Satellite System Total Electron Content and High Frequency sounding observations. The measured parameters of the majority of the disturbances allow classifying them as medium scale TIDs (MSTIDs). Overall, the observed climatology of ionospheric disturbances in the Antarctic Peninsula region varies significantly with the season and makes it possible to differentiate two major types of the disturbances: winter daytime and summer nighttime, based on their occurrence periods and characteristics. During the Antarctic summer period, the disturbances are present mainly during the nighttime and morning hours, when the background plasma density is at maximum (due to Weddell Sea Anomaly). These disturbances predominantly propagate northwestward and their occurrence probability is well correlated with the sporadic E layer observations, suggesting that these are electrified MSTIDs. During the winter, the TID events are almost exclusively observed during the daytime. The propagation direction of the disturbances during the daytime shows a strong correlation with the background neutral wind direction in the thermosphere. A possible mechanism for this effect is wind filtering of the Atmospheric Gravity Waves originating in the troposphere, which indicates that their source is in the lower atmosphere. The periods of the TIDs also significantly differ between the seasons. Wintertime TIDs have noticeably shorter periods (10–50 min) than those observed during other parts of the year (30–140 min), which also likely reflects the fact that the two types of TIDs are generated by different physical mechanisms.
more » « less- NSF-PAR ID:
- 10390953
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 127
- Issue:
- 11
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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