A ground‐based network of Global Navigation Satellite Systems receivers has been used to monitor medium‐scale traveling ionospheric disturbances (MSTIDs). MSTIDs were studied using total electron content perturbation maps and keograms over south‐southeast of Brazil during the period from December 2012 to February 2016. In total, 826 MSTIDs were observed mainly in daytime, thus presenting median values of horizontal wavelength, period, and horizontal phase velocity of 452 ± 107 km, 24 ± 4 min. and 323 ± 81 m/s, respectively. The direction of propagation varies on the season: during the winter (June–August), the waves preferentially propagated to north‐northeast, while in the other seasons the waves propagated to other directions. The anisotropy observed in the MSTID propagation direction could be associated with the region of the gravity wave generation that takes place in the troposphere. We also found that the MSTIDs were observed most frequently during the daytime, between 11 and 15 local time in winter and near to dusk solar terminator (17–19 local time) in the other seasons. Furthermore, the occurrence of MSTIDs was higher in winter. We suggest that atmospheric gravity waves in the thermosphere, mesosphere, and troposphere could play an important role in generating the MSTIDs and the propagation direction may depend on location of the wave sources.

Abstract. A ground-based network of GNSS receivers has been used to monitor equatorial plasma bubbles (EPBs) by mapping the total electron content (TEC map). The large coverage of the TEC map allowed us to monitor several EPBs simultaneously and get characteristics of the dynamics, extension and longitudinal distributions of the EPBs from the onset time until their disappearance. These characteristics were obtained by using TEC map analysis and the keogram technique. TEC map databases analyzed were for the period between November 2012 and January 2016. The zonal drift velocities of the EPBs showed a clear latitudinal gradient varying from 123 m s −1 at the Equator to 65 m s −1 for 35• S latitude. Consequently, observed EPBs are inclined against the geomagnetic field lines. Both zonal drift velocity and the inclination of the EPBs were compared to the thermospheric neutral wind, which showed good agreement. Moreover, the large two-dimensional coverage of TEC maps allowed us to study periodic EPBs with a wide longitudinal distance. The averaged values observed for the inter-bubble distances also presented a clear latitudinal gradient varying from 920 km at the Equator to 640 km at 30 • S. The latitudinal gradient in the inter-bubble distances seems to be related to the difference in the zonal drift velocity of the EPB from the Equator to middle latitudes and to the difference in the westward movement of the terminator. On several occasions, the distances reached more than 2000 km. Inter-bubble distances greater than 1000 km have not been reported in the literature.

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We simulate the primary and secondary atmospheric gravity waves (GWs) excited by the upward movement of air generated by the Hunga Tonga‐Hunga Ha'apai (hereafter “Tonga”) volcanic eruption on 15 January 2022. The Model for gravity wavE SOurce, Ray trAcing and reConstruction (MESORAC) is used to calculate the primary GWs and the local body forces/heatings generated where they dissipate. We add these forces/heatings to the HIgh Altitude Mechanistic general Circulation Model (HIAMCM) to determine the secondary GWs and large‐scale wind changes that result. We find that a wide range of medium to large‐scale secondary GWs with concentric ring structure are created having horizontal wind amplitudes of u′, v′ ∼ 100–200 m/s, ground‐based periods of τr ∼ 20 min to 7 hr, horizontal phase speeds of cH ∼ 100–600 m/s, and horizontal wavelengths of λH ∼ 400–7,500 km. The fastest secondary GWs with cH ∼ 500–600 m/s are large‐scale GWs with λH ∼ 3,000–7,500 km and τr ∼ 1.5–7 hr. They reach the antipode over Africa ∼9 hr after creation. Large‐scale temporally and spatially varying wind changes of ∼80–120 m/s are created where the secondary GWs dissipate. We analyze the Tonga waves measured by the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) on the National Aeronautics and Space Administration Ionospheric Connection Explorer (ICON), and find that the observed GWs were medium to large‐scale with cH ∼ 100–600 m/s and λH ∼ 800–7,500 km, in good agreement with the simulated secondary GWs. We also find good agreement between ICON‐MIGHTI and HIAMCM for the timing, amplitudes, locations, and wavelengths of the Tonga waves, provided we increase the GW amplitudes by ∼2 and sample them ∼30 min later than ICON.

Large‐scale traveling ionospheric disturbances (LSTIDs) were detected in both Northern and Southern Hemispheres over American sector during the geomagnetic storm on 17–18 March 2015, also known as the Saint Patrick's Day storm. Detrended total electronic content (dTEC) maps were made using dense GNSS network receiver data. The retrieved LSTIDs showed wavelengths of 1000 to 2000 km, phase velocity of ~300–1000 m/s, and period of ~30–50 min. Among them, three couples of LSTIDs were observed propagating from the polar regions to low latitudes. Two wave events observed in daytime showed the propagation direction of southwest in the Northern Hemisphere and northeast in the Southern Hemisphere, which means an asymmetric propagation against the geographic equator. The other wave event observed during the evening hour showed symmetric propagation direction, i.e., southwest in the Northern Hemisphere and northwest in the Southern Hemisphere, whereas their wavelength and phase velocity are significantly different between NH and SH. These observations indicate that the two groups of LSTID have different propagation conditions from polar to low‐latitude regions. The observed asymmetric/symmetric propagation forms suggest asymmetric/symmetric auroral current activity between the northern and southern polar regions.