Morphology Evolution of the Midlatitude Ionospheric Trough in Nighttime Under Geomagnetic Quiet Conditions

Abstract

The dynamics and climatology of midlatitude trough minimum have been widely investigated. However, the detailed magnetic local time (MLT) evolution of the trough walls (both equatorward and poleward) has not been well addressed. In this study, we used nearly 10‐year Planar Langmuir Probe (PLP) data from the CHAMP satellite to investigate how the location and shape of midlatitude trough evolve during night hours. We find that (1) the trough equatorward wall experiences an obvious equatorward extension in the premidnight sector, with steepness rapidly decreasing during the same local time sector; (2) the trough equatorward wall is as steep as poleward wall in the dusk sector; and (3) the trough poleward wall shows no remarkable change during the whole nighttime, except for a weakly reduced width and a slightly enhanced steepness near midnight. We suggest that the rapid extension of the equatorward wall in the premidnight sector is closely related to the plasma equatorward movement caused by the neutral winds. The rapid decrease of the steepness of the equatorward wall in the premidnight sector is not only influenced by its own width expansion but possibly also related to the upward plasma drift caused by neutral winds. The trough minimum and equatorward/poleward boundaries are found located at slightly higher magnetic latitude during equinoxes than that during solstice seasons.

Instability Mechanisms for the F‐Region Plasma Irregularities Inside the Midlatitude Ionospheric Trough: Swarm Observations

“…To focus on the plasma irregularities inside the MIT, the first step is to appropriately identify the MIT structure from the Swarm Ne orbital profiles. In a previous study, we proposed a method to identify a well‐structured MIT feature based on CHAMP Ne observations (Liu & Xiong, 2020). We have used the absolute value of temporal change rate of Ne (| Rt |) to determine the two MIT exterior boundaries.…”

“…Previous observations and simulations revealed some typical features of the MIT, such as the season, magnetic local time (MLT), and geomagnetic activity dependences (e.g., Karpachev, 2003; Rodger, 2008; Rodger et al., 1992; Spiro et al., 1978; Werner & Prölss, 1997). In addition, the longitudinal variation of the trough minimum (e.g., Aa et al., 2020; Karpachev et al., 2019; Liu et al., 2015; Yang et al., 2018) as well as widths and depths of the two MIT walls have also been discussed (e.g., He et al., 2011; Liu & Xiong, 2020; Voiculescu et al., 2010).…”

Relation of the Plasmapause to the Midlatitude Ionospheric Trough, the Sub‐Auroral Temperature Enhancement and the Distribution of Small‐Scale Field Aligned Currents as Observed in the Magnetosphere by THEMIS, RBSP, and Arase, and in the Topside Ionosphere by Swarm

“…Several mechanisms have been proposed as responsible for MIT formation. Plasma stagnation in the pre‐midnight sector (e.g., Rodger et al., 1992; Spiro et al., 1978), increased recombination rate and field‐aligned plasma flow as a result of frictional heating by SAID/SAPS in the dusk‐midnight MLT sector (Anderson et al., 1991, 1993; Rodger et al., 1992), and neutral winds (M. He et al., 2011; Liu & Xiong, 2020; Rodger et al., 1992), field aligned (M. He et al., 2011; Liu & Xiong, 2020; Rodger et al., 1992), and horizontal (Rodger et al., 1992; Shinbori et al., 2021; Voiculescu et al., 2006) plasma transport among others. The SETE is also believed to be produced by a combination of various factors: decreased cooling due to lower density, particle precipitation (Knudsen, 1974), heat conducted from the ring current along the field lines (Prölss, 2006), as well as frictional heating were proposed as possible heat sources (Anderson et al., 1991, 1993; Rodger et al., 1992).…”

Statistical Characteristics of Mid‐Latitude Ionospheric Irregularities at Geomagnetic Quiet Time: Observations From the Jiamusi and Hokkaido East SuperDARN HF Radars

“…These imply that neutral winds are not the main reason for the reversal of convection velocity. The distribution of the electron density gradient at the equatorward boundary of the mid-latitude ionospheric trough (Liu & Xiong, 2020) may be one of the factors for the velocity reversal structure by weakening the background northward ionospheric electric field (mainly from the high latitude convection pattern). For future studies, it is worthwhile and possible to combine the results of the mid-latitude electron density gradient, ionospheric conductivity, electric field, and convection distribution to further study the mechanisms of velocity reversal structures.…”