Mid-Latitude Daytime F2-Layer Disturbance Mechanism under Extremely Low Solar and Geomagnetic Activity in 2008–2009

Abstract

European near-noontime ionosonde observations were considered during the period of deep solar minimum in 2008–2009 to analyze foF2 perturbations not related to solar and geomagnetic activity. Sudden stratospheric warming (SSWs) events in January 2008 and 2009 were analyzed. An original method was used to retrieve aeronomic parameters from observed electron concentration in the ionospheric F-region. Atomic oxygen was shown to be the main aeronomic parameter responsible both for the observed day-to-day and long-term (during SSWs) foF2 variations. Atomic oxygen rather than neutral temperature mainly controls the decrease of thermospheric neutral gas density in the course of the SSW events. Day-to-day variations of thermospheric circulation and an intensification of eddy diffusion during SSWs are suggested to be the processes changing the atomic oxygen abundance in the upper atmosphere for the periods in question. Recent Global-Scale Observations of the Limb and Disk (GOLD) observations of O/N2 column density confirm the depletion of the atomic oxygen abundance not related to geomagnetic activity during SSWs.

Whether Sudden Stratospheric Warming Effects Are Seen in the Midlatitude Thermosphere of the Opposite Hemisphere?

“…Therefore, our selection of 30 January 2008 as a reference day is justified. Although the observations by Shepherd and Shepherd (2011) were made at 50°–70°N that is, at slightly larger latitudes than our stations are located (Table 1) our previous analysis (Mikhailov et al., 2021) has shown that Moscow, Juliusruh, and Chilton stations with latitudes >50°N demonstrated a decrease in foF 2 around the SSW peak similar to foF 2 variations at lower latitude Rome, Athens, Roquetes stations. Further, heights considered by Shepherd and Shepherd (2011) are above the turbopause level (∼120 km).…”

“…Column O/N 2 ratio calculated above the N 2 column density of 10 17 cm −2 (Strickland et al., 1995) manifests solely variations of atomic oxygen during SSW events and this was stressed earlier by Mikhailov et al. (2021).…”

“…Speaking about the reaction we mean a synchronous foF 2 decrease simultaneously observed at some midlatitude ionospheric stations of a given Hemisphere. This effect should be distinguished from day‐to‐day foF 2 variations (Mikhailov et al., 2021) which do not manifest the synchronism in their occurrence at different stations. The main thermospheric effect of SSWs is a global‐scale decrease of the atomic oxygen abundance in the upper atmosphere.…”

“…Column O/N 2 ratio which does not depend on the neutral temperature profile clearly manifests this seasonal difference in the atomic oxygen abundance (Figure 5, bottom). It should be stressed that O/N 2 ratio in fact indicates the column density of atomic oxygen (Mikhailov et al., 2021, their Figure 10).…”

SRF2—A Short‐Term (1–24)h foF2 Prediction Method

“…According to the present‐day understanding of the thermosphere‐ionosphere interaction, auroral heating by magnetospheric electric fields and particle precipitation is the main process controlling day‐to‐day variations of the thermosphere (e.g., Perrone et al., 2020; Mikhailov et al., 2021). The intensity of this heating depends on the level of geomagnetic activity; however, it takes place under low magnetic activity as well and F 2 ‐layer Q disturbances demonstrate this impact (Mikhailov et al., 2021; Perrone et al., 2020). Thermospheric circulation is equatorward during nighttime hours (Drob et al., 2015), transferring the perturbed neutral composition from the auroral zone to middle and lower latitudes.…”