Postmidnight ionospheric troughs in summer at high latitudes

Voiculescu, Mirela; Nygrén, T.; Aikio, Anita; Vanhamäki, Heikki; Pierrard, Viviane

doi:10.1002/2016ja023360

Cited by 16 publications

(19 citation statements)

References 38 publications

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“…The large eastward flow, upward flow, and enhanced ion temperature signatures in the high-latitude trough region have been observed simultaneously in previous studies (e.g. Jones et al, 1990;Voiculescu et al, 2016;Williams & Jain, 1986;Winser et al, 1986). These signatures suggest that the highlatitude trough formation is associated with the enhanced ion-electron recombination.…”

Section: Introductionsupporting

confidence: 73%

“…The high-latitude trough can be observed by incoherent scatter radars and satellites. The EISCAT radars are most used for the investigations of the high-latitude trough (Ishida et al, 2014;Vanhamaki et al, 2016;Voiculescu et al, 2016Voiculescu et al, , 2010Winser et al, 1986;Zou et al, 2013). Only some satellites' (OGO-4, ISIS 1) data are used for the investigations of the high-latitude trough (Grebowsky et al, 1983;Hruska et al, 1973;Horvath & Lovell, 2009aTaylor et al, 1975).…”

Section: Introductionmentioning

confidence: 99%

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The High‐Latitude Trough in the Southern Hemisphere Observed by Swarm‐A Satellite

Yang

et al. 2019

JGR Space Physics

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Based on the electron density, field-aligned currents (FACs) and ion drift velocity data from the Swarm-A satellite during 2013-2018, we investigate the features of the high-latitude trough in the Southern Hemisphere. The results show that the high-latitude trough in the Southern Hemisphere is a persistent postmidnight feature in winter. It is observed mainly in the eastern longitudes under low solar activity conditions and in a smaller longitudinal range under high solar activity conditions. The high-latitude trough moves to higher latitudes at later local times, which is more obvious under low solar activity conditions. We also find that the features of FACs and ion drift velocity distribution in the high-latitude trough region depend on longitude. In the longitude sector of 0°-70°E, the high-latitude trough positions are always located at the poleward boundary of the downward FAC region, and collocated with the convection reversal boundary in the postmidnight region. In the longitude sector of 80°-130°E, the high-latitude trough positions are located at the poleward boundary of the downward FAC region in the midnight region and at the strong westward or antisunward ion flow region in the postmidnight region. It is suggested that the highlatitude trough formation and evolution is possibly associated with downward FACs, flow stagnation in the convection reversal boundary, and westward or antisunward ion flow.Plain Language Summary Ionospheric troughs are depletions of the nighttime F region plasma density around the auroral and polar regions. The presence of the trough has a significant impact on the radio transmission. There are two types of troughs: the midlatitude trough and the high-latitude trough. The midlatitude trough locates on the equatorward side of the auroral oval, and the high-latitude trough locates within the auroral oval or polar cap. The features and formation mechanisms of the high-latitude trough in the Southern Hemisphere are not yet clear. This study uses a new multiparameter data set gathered by the Swarm-A satellite to find out the features and formation mechanisms of the high-latitude trough in the Southern Hemisphere. We found that the high-latitude trough in the Southern Hemisphere is a persistent postmidnight feature in winter. It is observed mainly in the eastern longitudes. The features of FACs and ion drift velocity distribution in the high-latitude trough region depend on longitude. The formation and evolution of the high-latitude trough is suggested to be associated with downward FACs, flow stagnation in the convection reversal boundary, and westward or antisunward ion flow.

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Section: Introductionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

The High‐Latitude Trough in the Southern Hemisphere Observed by Swarm‐A Satellite

Yang

et al. 2019

JGR Space Physics

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“…Considering the DAPS' location, the trough it may lead to is the high‐latitude trough (see Rodger et al, 1992, and references therein), whose relationship to ionospheric fast flows has been recognized (e.g., Ma et al, 2000; Williams & Jain, 1986). Especially, observations in the postmidnight sector have associated the high‐latitude trough with fast eastward flows (Vanhamäki et al, 2016; Voiculescu et al, 2016; Zou et al, 2013); the DAPS is also a fast eastward flow. The high‐latitude trough usually appears during substorm time (Ma et al, 2000; Zou et al, 2013) when we also expect DAPS to arise.…”

Section: Discussionmentioning

confidence: 99%

Dawnside Auroral Polarization Streams

et al. 2020

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Although the postmidnight‐to‐dawn sector of the auroral ionosphere contains interesting dynamic phenomena that may significantly impact the magnetosphere‐ionosphere‐thermosphere system, it has been much less studied than the dusk‐to‐premidnight sector. We discuss a dynamic phenomenon in the postmidnight‐to‐dawn sector of the auroral oval, eastward fast flows mainly within the expanse of the Region 1 current (its part equatorward of the polar cap). These flows peak and have a steep speed gradient (increase from low to high latitude) near the interface between the Region 1 and Region 2 currents. Because such flows correspond to an electric field that most likely comes from enhanced Region 2 currents and an associated spatial conductivity gradient, their generation mechanism is analogous to that of a subauroral polarization stream. Therefore, we refer to such an eastward flow as a dawnside auroral polarization stream (DAPS). We show several examples of the presence and absence of DAPS under different geomagnetic activity levels. A DAPS' electric field can heat the ionosphere (and thus the thermosphere), change the convection pattern of the magnetosphere‐ionosphere system, and modify the drift path of magnetospheric particles. Because a DAPS' flow peak maps to a major site of magnetic‐kinetic energy conversion in the magnetosphere (the transition region between dipole and stretched field), it may be important for the conversion. A DAPS' steep flow gradient is also potentially important; it may lead to instabilities, such as that responsible for auroral Omega bands. Given its potential importance, knowledge of DAPS is fundamental for understanding the magnetosphere‐ionosphere‐thermosphere system.

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“…In the stagnation region, where the westward convection flow within the dusk convection cell cancels the eastward corotation, the plasma decays due to the lack of the photoionization (Collis & Häggström, ; He et al, ; Ishida et al, ; Knudsen, ; Le et al, ; Nilsson et al, ; Rodger, ; Rodger, Moffett, & Quegan, ; Spiro, Heelis, & Hanson, ; Voiculescu et al, ; Yang, Le, & Liu, ). Another mechanism for plasma depletion relates to the increased recombination by frictional heating (Foster & Burke, ; Spiro, Heelis, & Hanson, ; Vanhamäki et al, ; Voiculescu et al, ), which is due to the large relative velocity between ionic and neutral components. The large poleward electric field associated with subauroral ion drifts (SAIDs) contributes to the large relative velocity (Rodger, ; Schunk et al, ).…”

Section: Introductionmentioning

confidence: 99%