Seasonal Oscillations of Thermosphere Neutral Density at Dusk/Dawn as Measured by Three Satellite Missions

Abstract

The thermosphere undergoes intra-annual oscillations in the mass density, composition and plasma density. The first (12-month period) and second (6-month period) harmonic components of these oscillations are considered as ''annual/semiannual'' or ''seasonal '' variation (Guo et al., 2008;Qian et al., 2009). The global average intra-annual oscillation is characterized by maxima near the equinoxes, a primary minimum spanning the boreal summer months and a secondary minimum spanning the boreal winter months. Ever since the intra-annual variation was first reported by Paetzold and Zschörner (1961) using satellite drag data, the annual and semiannual density oscillations of the thermosphere mass density, have been widely studied through observations and numerical simulations (e.g., Bowman et al., 2008;Fuller-Rowell, 1998;Picone et al., 2002). The amplitude of typical global annual oscillation (residual density relative to the mean density) at 400 km in solar minimum is ∼10% (Emmert & Picone, 2010), while the amplitude of the global semiannual oscillations in thermospheric mass density at 400 km (e.g., Emmert, 2015a;Jones et al., 2017) and ionospheric TEC (e.g., Jones et al., 2017;Lean et al., 2011) are typically ∼15%. The annual oscillation shows a strong hemispherically asymmetric latitude dependence with a higher annual amplitude at high latitudes in the southern hemisphere than that in the northern hemisphere (e.g., Lean et al., 2016;Lei et al., 2012). The neutral density data from satellite missions such as GOCE, the Challenging Minisatellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE) have been used to derive intra-annual variations of the thermosphere (e.g., Guo et al., 2008;Weng et al., 2018). The seasonal variation of thermospheric composition, such as the column density ratio ∑O/N 2 , the ratio of O/ N 2 at single pressure level and carbon dioxide emissions observed by the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft (e.g., Weimer et al., 2018;Yu et al., 2020;Yue et al., 2019), and the ∑O/N 2 derived from the NASA Global Observations of Limb and Disk (GOLD) mission (Qian et al., 2022), have also been studied. The seasonal variation also exists in the ionosphere. The intra-annual variations in the ionosphere, such as those in the maximum electron density of the F 2 layer N m F 2 , the F 2 -layer height h m F 2 , and the total electron content were reported (e.g.

Evaluation of TIEGCM based on GOCE neutral density

“…[8] studied the seasonal variation of the thermospheric mass density of GOCE at dawn/dusk. Similarly, [9] investigated the annual and semi-annual variations of the dawn/dusk thermospheric mass density over a certain altitude range based on the neutral density of the GOCE satellite. [10] used GOCE transorbital wind measurements to explore the intra-annual oscillations (IAOs) of the upper thermospheric winds between 70 °S and 70 °N. With the accumulation of observations, modeling work has also prominently developed in the past few decades.…”