An olden but golden EISCAT observation of a quiet‐time ionospheric trough

Voiculescu, Mirela; Nygrén, T.; Aikio, Anita; Kuula, R.

doi:10.1029/2010ja015557

Cited by 20 publications

(23 citation statements)

References 32 publications

(80 reference statements)

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“…We defined a region of decreasing electron density, the minima of which were at least 20% lower than the background value; this region was then identified as the trough region. Our data confirm that a 20% decrease is sufficient to distinguish the trough events from the nontrough events; with this value we are able to detect trough events referred to in past studies [e.g., Collis and Häggström, 1988;Voiculescu et al, 2010]. Additionally, to verify this threshold, we showed that the trough characteristics detailed below (section 3) did not change upon increasing this value, i.e., that the trough characteristics could be obtained using a threshold of just 20%.…”

Section: Discussionsupporting

confidence: 87%

Seasonal variation and solar activity dependence of the quiet‐time ionospheric trough

et al. 2014

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We have conducted a statistical analysis of the ionospheric F region trough, focusing on its seasonal variation and solar activity dependence under geomagnetically quiet and moderate conditions, using plasma parameter data obtained via Common Program 3 observations performed by the European Incoherent Scatter (EISCAT) radar between 1982 and 2011. We have confirmed that there is a major difference in frictional heating between the high-and low-latitude sides of the EISCAT field of view (FOV) at 73°0′N-60°5′N (geomagnetic latitude) at an altitude of 325 km, which is associated with trough formation. Our statistical results show that the high-latitude and midlatitude troughs occur on the high-and low-latitude sides of the FOV, respectively. Seasonal variations indicate that dissociative recombination accompanied by frictional heating is a main cause of trough formation in sunlit regions. During summer, therefore, the occurrence rate is maintained at 80-90% in the postmidnight high-latitude region owing to frictional heating by eastward return flow. Solar activity dependence on trough formation indicates that field-aligned currents modulate the occurrence rate of the trough during the winter and equinox seasons. In addition, the trough becomes deeper via dissociative recombination caused by an increased ion temperature with F 10.7 , at least in the equinox and summer seasons but not in winter.

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Section: Discussionsupporting

confidence: 87%

Seasonal variation and solar activity dependence of the quiet‐time ionospheric trough

et al. 2014

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“…One mechanism for trough formation in the premidnight sector, confirmed by numerous studies, is the stagnation mechanism: eastward corotation cancels the westward convection, plasma stagnates in the nonilluminated areas, and its density drops due to lack of solar (UV) ionization [Rodger et al, 1992;Nilsson et al, 2005;Voiculescu et al, 2010;Voiculescu and Nygrén, 2007]. However, one can safely assume that the plasma is depleted by a mechanism that acts on a continuous basis and produces a trough that is visible during some time in different locations.…”

Section: Discussionmentioning

confidence: 97%

“…The plasma decays due to lack of photoionization [Whalen, 1989;Rodger et al, 1992;Nilsson et al, 2005;Voiculescu et al, 2010;Spiro et al, 1978]. The plasma decays due to lack of photoionization [Whalen, 1989;Rodger et al, 1992;Nilsson et al, 2005;Voiculescu et al, 2010;Spiro et al, 1978].…”

Section: 1002/2016ja023360mentioning

confidence: 99%

Postmidnight ionospheric troughs in summer at high latitudes

et al. 2016

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In this article we identify possible mechanisms for the formation of postmidnight ionospheric troughs during summer, in sunlit plasma. Four events were identified in measurements of European Incoherent Scatter and ESR radars during CP3 experiments, when the ionosphere was scanned in a meridional plan. The spatial and temporal variation of plasma density, ion, and electron temperatures were analyzed for each of the four events. Super Dual Auroral Radar Network plasma velocity measurements were added, when these were available. For all high‐latitude troughs the ion temperatures are high at density minima (within the trough), at places where the convection plasma velocity is eastward and high. There is no significant change in electron temperature inside the trough, regardless of its temporal evolution. We find that troughs in sunlit plasma form in two steps: the trough starts to form when energetic electron precipitation leads to faster recombination in the F region, and it deepens when entering a region with high eastward flow, producing frictional heating and further depleting the plasma. The high‐latitude plasma convection plays an important role in formation and evolution of troughs in the postmidnight sector in sunlit plasma. During one event a second trough is identified at midlatitudes, with different characteristics, which is most likely produced by a rapid subauroral ion drift in the premidnight sector.

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“…Methods of observation include the following: ionospheric sounders such as the networks considered by Whalen (1987Whalen ( , 1989; incoherent scatter radar, which can reveal the latitudinal structure of the trough and associated ionization temperature characteristics (Voiculescu et al, 2010); satellite TEC observations, for example by the Navy Ionospheric Monitoring System, NIMS (Kersley et al, 2004); and ionospheric tomography reconstruction using NIMS TEC observations . In more recent years TEC measurements using GPS radio transmissions have been used to observe and study the trough, for example Krankowski et al (2009) who used GPS observations from a network of receiving stations in Europe.…”

Section: Introductionmentioning

confidence: 99%

Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

et al. 2018

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Abstract. The main ionospheric trough is a large-scale spatial depletion in the electron density distribution at the interface between the high-and mid-latitude ionosphere. In western Europe it appears in early evening, progresses equatorward during the night, and retreats rapidly poleward at dawn. It exhibits substantial day-to-day variability and under conditions of increased geomagnetic activity it moves progressively to lower latitudes. Steep gradients on the trough-walls on either side of the trough minimum, and their variability, can cause problems for radio applications. Numerous studies have sought to characterize and quantify the trough behaviour.The Electron Density Assimilative Model (EDAM) models the ionosphere on a global scale. It assimilates observations into a background ionosphere, the International Reference Ionosphere 2007 (IRI2007), to provide a full 3-D representation of the ionospheric plasma distribution at specified times and days. This current investigation studied the capability of EDAM to model the ionosphere in the region of the main trough. Total electron content (TEC) measurements from 46 GPS stations in western Europe from September to December 2002 were assimilated into EDAM to provide a model of the ionosphere in the trough region. Vertical electron content profiles through the model revealed the trough and the detail of its structure. Statistical results are presented of the latitude of the trough minimum, TEC at the minimum and of other defined parameters that characterize the trough structure. The results are compared with previous observations made with the Navy Ionospheric Monitoring System (NIMS), and reveal the potential of EDAM to model the large-scale structure of the ionosphere.

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An olden but golden EISCAT observation of a quiet‐time ionospheric trough

Cited by 20 publications

References 32 publications

Seasonal variation and solar activity dependence of the quiet‐time ionospheric trough

Seasonal variation and solar activity dependence of the quiet‐time ionospheric trough

Postmidnight ionospheric troughs in summer at high latitudes

Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

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