Characteristics of Ionospheric Storm on October 13, 2016 at the Greenwich Meridian

Abstract

The geomagnetic storms are the disturbances of the Earth's magnetic field, and the impact of solar wind particles enhancement (Buonsanto, 1999;Gonzalez et al., 1994;Kumar & Kumar, 2019). Following geomagnetic storms, the ionosphere also has obvious disturbance. It shows the critical frequency of F2-layer (foF2) or total electron content (TEC) changes obviously. The large decrease of foF2 or TEC is the ionospheric negative storm, and the significant increase of foF2 or TEC is referred to as positive storms (Fagundes et al., 2016;Maruyama et al., 2004). In general, 𝐴𝐴 𝐴𝐴 region ionization is positively correlated to the density ratio of atomic oxygen [O] to the molecular nitrogen 𝐴𝐴 [N2] . Prölss (1987) showed that the negative storm was caused by the change of neutral gas composition. The enhanced ratio of 𝐴𝐴 [N2] /[O] would lead to the chemical loss rate increase, so the ionospheric electron density decreased.There are two main physical mechanisms of ionospheric positive storms. The first is the equatorward wind surge or disturbance wind (Fuller-Rowell et al., 1994). Joule heating raises the temperature of the upper thermosphere and ion drag drives high velocity neutral winds. The heat source drives a global disturbance wind. It propagates to low latitudes and even into the opposite hemisphere. The equatorward wind pushes the ionosphere up to high altitudes where the recombination is ineffective. As a result, the electron density increases under sunlit conditions (Maruyama et al., 2004;Zhao et al., 2008). Because the equatorward wind surge blows from high to low latitudes, the ionospheric disturbance has time delay. During quiet days, the neutral winds (or background winds) are poleward in daytime and turn equatorward after sunset. During storms, the neutral winds are the combination of background and disturbance winds. The daytime neutral wind, which is caused by Joule heating in the auroral region, even turns to equatorward (Fuller-Rowell et al., 1994). Different storms have different intensity, local time, and latitude coverage. de Jesus et al. ( 2016) studied a positive ionospheric storm at equatorial, low and middle latitudes in African sector. The factor was the equatorward disturbance winds and huge wind circulations.

The Ionospheric Dynamics of the African Sector Responding to a Severe Geomagnetic Storm; the Storm of 3–5 November 2021

“…This was calculated as the slope of each arrow showing the direction of the equatorward propagating TAD from either midlatitude, given that the time of the start of the TEC enhancement in each midlatitude is ∼0600 UT and the time of the maximum TEC peak (∼70 TECu) observed at around the magnetic equator is ∼1200 UT. This magnitude of the calculated velocity is small compared to the estimated velocity of the traveling disturbance in the high and mid-latitudes approximated to be about 400-1000 m/s (Bruinsma & Forbes, 2009;Wan et al, 2021;Zhang et al, 2019). This is because the low velocities are caused by high daytime electron densities in the low latitudes which increase the resistance of ion drag force that slows the disturbance in the low latitude regions.…”

“…Table 2 shows the time of maximum storm TEC enhancement and dTEC peaks in UT and LT at each GNSS station. We know that the effect of the PPEF is simultaneous storm effects of TEC enhancement at all latitudes on the same time (Wan et al., 2021). However, we observe time delays for maximum TEC at each GNSS station increasing towards the equatorial region from the midlatitude stations.…”

“…These are associated with gravity waves, which later manifest as traveling atmospheric disturbances (TADs) propagating equatorward in the mid and low‐latitude regions. These have been studied to cause the storm time‐induced ionospheric disturbances in TEC, electron density, and other ionospheric parameters in the low latitude ionosphere (Habarulema et al., 2016; Moges et al., 2022; Ngwira et al., 2012; Wan et al., 2021) and references there in. It should be noted however, there can be a possibility of the existence of poleward and equatorward TIDs simultaneously during storm periods (Habarulema et al., 2016).…”

“…This is because the low velocities are caused by high daytime electron densities in the low latitudes which increase the resistance of ion drag force that slows the disturbance in the low latitude regions. In the study by Wan et al (2021), he showed that the speed of the TAD was decreasing as it propagated from a high to the mid-latitude region during a storm period on 13 October 2016.…”

“…These propagate to low latitudes regions blowing the F2 region ionosphere to high altitudes with the smallest recombination rates and hence electron density and TEC increases. Strong and severe disturbances can cross the equatorial region to the other hemisphere and are associated with a time delay observed at different latitudinal positions (Wan et al., 2021). The neutral wind pattern during quiet days is poleward during the day and equatorward during the night, however strong geomagnetic storms can induce an opposite disturbance in wind circulation pattern with a daytime equatorward neutral wind.…”