Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation

Schlatter, Nicola; Ivchenko, Nickolay; Sergienko, T.; Gustavsson, B.; Brändström, Urban

doi:10.5194/angeo-31-1681-2013

Cited by 11 publications

(21 citation statements)

References 30 publications

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“…Sullivan et al, 2008), the SLT-like anomalous echoes in this study were found to be closely related to energetic precipitation, characteristic of discrete aurora. This is in accordance with the event study of a similar zero Doppler shift feature seen during high-energy precipitation discussed by Schlatter et al (2013). However, modelling studies (Isham et al, 2012;Akbari et al, 2016) point to the low energy part of the electron spectrum as being efficient in exciting the Langmuir turbulence.…”

Section: Discussionsupporting

confidence: 89%

Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation

Dahlgren¹,

Schlatter²,

Ivchenko³

et al. 2017

Ann. Geophys.

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Abstract. Non-thermal echoes in incoherent scatter radar observations are occasionally seen in the high-latitude ionosphere. Such anomalous echoes are a manifestation of plasma instabilities on spatial scales matching the radar wavelength. Here we investigate the occurrence of a class of spatially localized anomalous echoes with an enhanced zero Doppler frequency feature and their relation to auroral particle precipitation. The ionization profile of the E region is used to parametrize the precipitation, with nmE and hmE being the E region peak electron density and the altitude of the peak, respectively. We find the occurrence rate of the echoes to generally increase with nmE and decrease with hmE, thereby indicating a correlation between the echoes and high-energy flux precipitation of particles with a high characteristic energy. The highest occurrence rate of > 20 % is found for hmE = 109 km and nmE = 10 11.9 m −3 , averaged over the radar observation volume.

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Section: Discussionsupporting

confidence: 89%

Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation

Dahlgren¹,

Schlatter²,

Ivchenko³

et al. 2017

Ann. Geophys.

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“…The vertical extent of these structures has not been investigated systematically, although several examples of density enhancements associated with these structures have been presented. Thus Schlatter et al (2013) examined density enhancements due to high-energy auroral precipitation in the E and F region between ∼ 100 and ∼ 150 km; see their Fig. 1a.…”

Section: Discussionmentioning

confidence: 99%

A modeling study of asymmetries in plasma irregularity characteristics near gradient reversals

Lamarche

Makarevich

2016

Ann. Geophys.

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Abstract. Asymmetries in plasma density irregularity generation between the leading and trailing edges of the largescale plasma density structures in the high-latitude ionosphere are investigated. A model is developed that evaluates the gradient-drift instability (GDI) growth rate differences across the gradient reversal that is applicable at all propagation directions and for the broad range of altitudes spanning the entire lower ionosphere. In particular, the model describes asymmetries that would be observed by an oblique scanning radar near density structures in the polar cap such as elongated polar patches. The dependencies on the relative orientations between the directions of the gradient reversal, plasma convection, and wave propagation are examined at different altitudinal regions. At all altitudes, the largest asymmetries are expected for observations along the gradient reversals, e.g., when an elongated structure is oriented along the radar boresight. The convection direction that results in the strongest asymmetries exhibits a strong dependence on the altitude, with the optimal convection being parallel to the gradient reversal in the E region, perpendicular to it in the F region, and at some angle between these extremes in the transitional region. Implications for observations of polar patches by oblique scanning radars within the Super Dual Auroral Radar Network are discussed. It is demonstrated that the wave propagation direction relative to the prevalent convection and gradient directions plays a critical role in controlling both the irregularity growth rate and its asymmetries near gradient reversals.

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“…Such events are referred to as naturally enhanced ion acoustic lines (NEIALs) [ Foster et al , ; Michell et al , ; Michell and Samara , ; Kontar and Pėcseli , ; Strømme et al , ]. NEIALs are captured as echoes which enhance one or both ion line shoulders in the typical power spectrum by 1–2 orders of magnitude [ Rietveld et al , ; Collis et al , ], and enhancements up to 5 orders of magnitude have been reported as well [ Schlatter et al , ]. NEIALs have been observed in field‐aligned measurements of incoherent scatter radars (ISRs).…”

Section: Introductionmentioning

confidence: 99%

On the contribution of thermal excitation to the total 630.0 nm emissions in the northern cusp ionosphere

Kwagala

Oksavik

Lorentzen³

et al. 2017

JGR Space Physics

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Direct impact excitation by precipitating electrons is believed to be the main source of 630.0 nm emissions in the cusp ionosphere. However, this paper investigates a different source, 630.0 emissions caused by thermally excited atomic oxygen O(1D) when high electron temperature prevail in the cusp. On 22 January 2012 and 14 January 2013, the European Incoherent Scatter Scientific Association (EISCAT) radar on Svalbard measured electron temperature enhancements exceeding 3000 K near magnetic noon in the cusp ionosphere over Svalbard. The electron temperature enhancements corresponded to electron density enhancements exceeding 1011 m−3 accompanied by intense 630.0 nm emissions in a field of view common to both the EISCAT Svalbard radar and a meridian scanning photometer. This offered an excellent opportunity to investigate the role of thermally excited O(1D) 630.0 nm emissions in the cusp ionosphere. The thermal component was derived from the EISCAT Radar measurements and compared with optical data. For both events the calculated thermal component had a correlation coefficient greater than 0.8 to the total observed 630.0 nm intensity which contains both thermal and particle impact components. Despite fairly constant solar wind, the calculated thermal component intensity fluctuated possibly due to dayside transients in the aurora.

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Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation

Cited by 11 publications

References 30 publications

Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation

Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation

A modeling study of asymmetries in plasma irregularity characteristics near gradient reversals

On the contribution of thermal excitation to the total 630.0 nm emissions in the northern cusp ionosphere

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