Low‐altitude satellite measurements of pulsating auroral electrons

Samara, M.; Michell, R.; Redmon, R. J.

doi:10.1002/2015ja021292

Cited by 17 publications

(26 citation statements)

References 28 publications

(28 reference statements)

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“…The above proposal is admittedly tentative so far and subject to future investigations from both experimental and theoretical aspects. We, however, note that the existence of low-energy electron precipitation during pulsating auroral intervals was previously reported by, e.g., Jones et al [2009], Liang et al [2015a], and Samara et al [2010Samara et al [ , 2015, though none of the above literature considered the low-energy electron precipitation as a possible cause of pulsating auroras. However, clues of low-energy electron precipitation in direct association with pulsating auroras do occasionally exist in our past experiences with pulsating auroras.…”

Section: Discussionmentioning

confidence: 59%

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On the 630 nm red‐line pulsating aurora: Red‐line Emission Geospace Observatory observations and model simulations

et al. 2016

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In this study, we present observations of red‐line (630 nm) pulsating auroras using the camera system of Red‐line Emission Geospace Observatory (REGO), during a geomagnetic storm interval. We also develop a time‐dependent model to simulate the 630 nm auroral pulsations in response to modulated precipitation inputs and compare the model outputs with REGO observations. Key results are as follows. (1) Notwithstanding the long radiative timescale of the 630 nm emission, red‐line auroras can still be modulated by pulsating electron precipitations and feature noticeable oscillations, which constitute the red‐line pulsating auroral phenomena. (2) In a majority of cases, the oscillation magnitude of red‐line pulsating auroras is substantially smaller than that of the concurrent pulsating auroras seen on Thermal Emission Imaging System whitelight images (generally dominated by 557.7 nm green‐line emissions). Under certain circumstances, e.g., when the characteristic energy of the precipitation is very high, some of the pulsating auroras may not show discernible imprints on red line. (3) The altitude range contributing most to the red‐line pulsating aurora is systematically lower than that of the steady‐state red‐line aurora, since the slower O(1D) loss rate at higher altitudes tends to suppress the oscillation range of the 630 nm emission rate. (4) We find that some pulsating auroral patches are characterized by enhanced red‐to‐green color ratio during their on time, hinting that the percentage increase of the red‐line auroral component exceeds that of the green‐line auroral component for those patches. We suggest that those special patches might possibly be associated with lower energy (<1 keV) electron precipitations.

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Section: Discussionmentioning

confidence: 59%

“…[], and Samara et al . [, ], though none of the above literature considered the low‐energy electron precipitation as a possible cause of pulsating auroras. However, clues of low‐energy electron precipitation in direct association with pulsating auroras do occasionally exist in our past experiences with pulsating auroras.…”

Section: Discussionmentioning

confidence: 99%

On the 630 nm red‐line pulsating aurora: Red‐line Emission Geospace Observatory observations and model simulations

et al. 2016

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“…On the other hand, Samara et al . [] reported a reduction of <1 keV soft electron precipitation fluxes in a few pulsating auroral events. To the authors' knowledge, there is so far no evidence that the soft electron precipitation of hundreds of eV could be a statistically common feature accompanying pulsating auroras, though its occasional existence and causal effect on electron heating in the F region ionosphere might likely be present in some of our events.…”

Section: Discussionmentioning

confidence: 99%

Ionospheric electron heating associated with pulsating auroras: A Swarm survey and model simulation

et al. 2017

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In this paper we report a study on the plasma signatures (electron temperature, plasma density, and field‐aligned current) of patchy pulsating auroras in the upper F region ionosphere using Swarm satellite data. Via a survey of 38 patch crossing events, we repeatedly identify a strong electron temperature enhancement associated with the pulsating aurora. On average, the electron temperature at Swarm satellite altitudes (~460 km) increases from ~2200 K at subauroral latitudes to a peak of ~3000 K within the pulsating auroral patch. This indicates that pulsating auroras may act as an important heating source for the nightside ionosphere. On the other hand, no well‐defined trend of plasma density variations associated with pulsating auroras is identified at Swarm altitudes. The field‐aligned currents within the pulsating aurora patch are mostly upward, with mean magnitudes on order of ~1 μA/m2. We then perform a numerical simulation to explore the potential mechanisms underlying the strong electron heating associated with the pulsating aurora. Via simulations we find that to account for the realistic electron temperature observation in a major portion of our events, pulsating auroras are likely accompanied by substantial magnetospheric heat fluxes around the order of ~1010 eV/cm2. We propose that such magnetospheric heat fluxes may be pertinent to one long‐hypothesized feature of pulsating auroras, namely, the coexistence of an enhanced low‐energy plasma population in magnetic flux tubes threading the pulsating aurora, in addition to the energetic electron precipitation. Via a Swarm survey we repeatedly find a strong electron temperature enhancement associated with the pulsating aurora The field‐aligned currents within pulsating auroras are moderately upward, with mean magnitudes on the order of ~1e−6 A/m2 To explain the observed electron heating, pulsating auroras are likely accompanied by magnetospheric heat fluxes around ~1E+10 eV/cm2/s.

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“…The measured electron energies associated with pulsating aurora also cover a large range, from as low as 1 keV [ McEwan et al , ], 5 to 12 keV [ Johnstone , ; Smith et al , ; Samara et al , ], >20 keV [ Stenbaek‐Nielsen and Hallinan , ; Samara et al , ], and 30–50 keV [ Jaynes et al , ] to as high as 140 keV [ Sandahl et al , ]. High time resolution Reimei satellite observations in conjunction with optical imaging have shown pulsating aurora to be associated with 8 keV to 12 keV electron precipitation [ Samara et al , ; Miyoshi et al , ; Nishiyama et al , ].…”

Section: Introductionmentioning

confidence: 99%

First optical observations of interhemispheric electron reflections within pulsating aurora

Samara

Michell

Khazanov

2017

Geophysical Research Letters

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A case study of a pulsating auroral event imaged optically at high time resolution presents direct observational evidence in agreement with the interhemispheric electron bouncing predicted by the SuperThermal Electron Transport model. “Pulsation‐on” times are identified and subsequent equally spaced fainter pulsations are also noted and can be explained by a portion/percentage of the primary precipitating electrons reflecting upward from the ionosphere, traveling to the opposite hemisphere and reflecting upward again. The high time resolution of these data, combined with the short duration of the pulsation‐on time (∼1 s) and the relatively long spacing between pulsations (∼6 to 9 s) made it possible to observe the faint optical pulses caused by the reflected electrons coming from the opposite hemisphere.

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Low‐altitude satellite measurements of pulsating auroral electrons

Cited by 17 publications

References 28 publications

On the 630 nm red‐line pulsating aurora: Red‐line Emission Geospace Observatory observations and model simulations

On the 630 nm red‐line pulsating aurora: Red‐line Emission Geospace Observatory observations and model simulations

Ionospheric electron heating associated with pulsating auroras: A Swarm survey and model simulation

First optical observations of interhemispheric electron reflections within pulsating aurora

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