Abstract
Abstract. The stratification phenomenon is investigated using the simultaneous in situ plasma density measurements obtained by the Swarm satellites orbiting at different altitudes above the F2 peak. For the first time, the continuous distribution morphology and the exact locations are obtained for the nighttime stratification, which show that the stratification events are centered at the EIA (equatorial ionization anomaly) trough and extend towards the two EIA crests, with the most significant part being located at the EIA trough. Another new discovery is the stratification in southern mid-latitudes; stratification events in this region are located on a local plasma peak sandwiched by two lower density strips covering all the longitudes. The formation mechanism of the stratification for the two latitudinal regions is discussed, but the stratification mechanism in southern mid-latitudes remains an unsolved problem. Highlights. This paper addresses the following: first application of in situ plasma densities for the direct analysis of the stratification in F2 layer, refined features of the exact location and continuous morphology for the stratification phenomenon, a new discovery of stratification covering all longitudes in southern mid-latitudes.
Highlights
Stratification is a kind of phenomenon appearing in the ionospheric F2 layer at low latitudes near the geomagnetic equator, where an additional layer is shown above the F2 layer peak due to the combined effect of the upward E × B drift at the geomagnetic equator and the meridional neutral wind (Balan et al, 1997, 1998; Jenkins et al, 1997)
All these studies have shown that stratification above the F2 peak is a regular rather than an anomalous phenomenon appearing both during the day and at night and is limited to a narrow zone near the geomagnetic equator regions, and the occurrence of this stratification phenomenon depends on the season, solar activity, and geomagnetic activity (Balan et al, 2008; Batista et al, 2002; Jenkins et al, 1997; Zhao et al, 2011a)
The global distribution of the detected stratification events from all the co-located orbit pairs from January to June 2014 is given in Fig. 3; given in this figure are the variations in the occurrence number with the local time and month
Summary
Stratification is a kind of phenomenon appearing in the ionospheric F2 layer at low latitudes near the geomagnetic equator, where an additional layer is shown above the F2 layer peak due to the combined effect of the upward E × B drift at the geomagnetic equator and the meridional neutral wind (Balan et al, 1997, 1998; Jenkins et al, 1997). Since stratification was first reported in the mid-20th century (Sen, 1949; Skinner et al, 1954), many studies have been conducted to study the formation mechanism and diurnal, seasonal, and solar-activity dependence of this phenomenon using different measurements, such as groundbased ionospheric sounding ionograms (Balan et al, 1997; Batista et al, 2002; Jenkins et al, 1997; Zhao et al, 2011a), ground-based TEC (total electron content; Thampi et al, 2005), satellite-based ionospheric sounding ionograms (Depuev and Pulinets, 2001; Karpachev et al, 2013; Lockwood and Nelms, 1964), satellite-based radio occultation (RO) observations (Zhao et al, 2011b), and satellite-based in situ measurements (Wang et al, 2019) All these studies have shown that stratification above the F2 peak is a regular rather than an anomalous phenomenon appearing both during the day and at night and is limited to a narrow zone near the geomagnetic equator regions, and the occurrence of this stratification phenomenon depends on the season, solar activity, and geomagnetic activity (Balan et al, 2008; Batista et al, 2002; Jenkins et al, 1997; Zhao et al, 2011a). The morphology of the stratification along the latitudinal direction can be obtained using the continuous measurements
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