Abstract
Abstract. Many studies have revealed the stratification phenomenon of the topside ionospheric F2 layer using ground-based or satellite-based ionograms, which can show direct signs of this phenomenon. However, it is difficult to identify this phenomenon using the satellite-based in situ electron density data. Therefore, a statistical method, using the shuffle resampling skill, is adopted in this paper. For the first time, in situ electron density data, recorded by the same Langmuir probe aboard the DEMETER (Detection of Electro-Magnetic Emission Transmitted from Earthquake Regions) satellite at different altitudes, are analyzed, and a possible stratification phenomenon is identified using the proposed method. Our results show that the nighttime stratification, possibly a permanent phenomenon, can cover most longitudes near the geomagnetic equator, which is not found from the daytime data. The arch-like nighttime stratification decreases slowly on the summer hemisphere and thus extends a larger latitudinal distance from the geomagnetic equator. All results, obtained by the proposed method, indicate that the stratification phenomenon is more complex than what has previously been found. The proposed method is thus an effective one, which can also be used in similar studies of comparing fluctuated data.
Highlights
The results show that there are both cases of significant differences and insignificant differences between the data observed at different altitudes and between the data observed at same altitudes
According to the data grouping and calculation method, if the phenomenon is only due to random data fluctuation, the possibility that this phenomenon appears only for data recorded at different altitudes and at several latitudinal regions in the vicinity of the geomagnetic equator at the same www.ann-geophys.net/37/645/2019/
To compare the in situ electron density data observed by the DEMETER Satellite at different altitudes, a statistical method, using the permutation resampling skill, is adopted and used to carry out the data comparison and analysis work
Summary
Stratification of the F2 layer, an enhancement in electron density at heights above the F2-layer maximum in the ionosphere at low latitudes and mid-latitudes, was first reported in the mid-20th century (Heisler, 1962; Sen, 1949; Skinner et al, 1954). Sayers et al (1963) was the first to detect topside ledges in the equatorial ionosphere using a Langmuir probe aboard the Ariel I satellite and predicted that the topside ionograms would reveal the ledges as cusps, as later proved by many studies using the topside sounding technique (Lockwood and Nelms, 1964; Raghavarao and Sivaraman, 1974; Sharma and Raghavarao, 1989).There were few studies of the stratification phenomenon until the mid-1990s. Balan and Bailey (1995) explained the formation mechanism of the F3 layer using the SUPIM (Sheffield University Plasmasphere–Ionosphere Model). Stratification of the F2 layer, an enhancement in electron density at heights above the F2-layer maximum in the ionosphere at low latitudes and mid-latitudes, was first reported in the mid-20th century (Heisler, 1962; Sen, 1949; Skinner et al, 1954). Balan and Bailey (1995) explained the formation mechanism of the F3 layer using the SUPIM (Sheffield University Plasmasphere–Ionosphere Model). There were few studies of the stratification phenomenon until the mid-1990s. They referred to the layer as G layer, which was later renamed as F3 layer because it has the same chemical composition as the F region (Balan et al, 1997). Many more studies on the mechanism and spatial and temporal distributions of the phenomenon have been carried out (Batista et al, 2002; Depuev and Pulinets, 2001; Hsiao et al, 2001; Rama Rao et al, 2005; Tardelli et al, 2016; Uemoto et al, 2007; Zain et al, 2008; Zhao et al, 2011a, b)
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