Ground-based observations of diffuse auroral structures in conjunction with Reimei measurements

Samara, M.; Michell, R.; Asamura, Kazushi; Hirahara, Masafumi; Hampton, Donald; Stenbaek‐Nielsen, H. C.

doi:10.5194/angeo-28-873-2010

Cited by 18 publications

(13 citation statements)

References 28 publications

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“…[], 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%

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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: 99%

“…Using joint observations from the Reimei satellite and a meridian‐scanning photometer, Samara et al . [] showed a 630 nm emission enhancement together with both high‐ and low‐energy electron precipitation flux structures. Shiokawa et al .…”

Section: Introductionmentioning

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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“…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 , ]. These variations in observed electron precipitation energies show that there are many different types of pulsating aurora, likely indicating different generation mechanisms and different ionospheric effects.…”

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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“…It typically occurs on the postmidnight sector near the equatorward boundary of the auroral oval and covers a local time range that increases with increasing geomagnetic activity, even extending as far as to the dayside [ Royrvik and Davis , 1977; Oguti et al , 1981; Jones et al , 2011]. On the basis of rocket and low‐altitude spacecraft measurements made simultaneously with auroral imaging, such auroral pulsations are known to be caused by quasiperiodic precipitation of electrons with energies of tens of keV into the upper atmosphere [ Johnstone , 1978; Sandahl et al , 1980; Samara et al , 2010].…”

Section: Introductionmentioning

confidence: 99%

Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions

et al. 2011

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[1] A multievent study was performed using conjugate measurements of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and an all-sky imager during periods of intense lower-band chorus waves. The thirteen identified cases support our previous finding, based on two events, that the intensity modulation of lower-band chorus near the magnetic equator is highly correlated with quasiperiodic pulsating auroral emissions near the spacecraft's magnetic footprint, indicating that lower-band chorus is the driver of the pulsating aurora. Furthermore, we identified a fortuitous measurement made simultaneously by two THEMIS spacecraft with small spatial separation. The two spacecraft were found to be located in a single pulsating chorus patch and the spacecraft footprints were in the same pulsating auroral patch when intense chorus bursts were measured simultaneously, whereas only one of the spacecraft's footprints was in a patch when the other spacecraft did not detect intense chorus. On the basis of this event, we can estimate the pulsating chorus patch size by mapping the pulsating auroral patches from the ionosphere toward the magnetic equator, giving a roughly circular region of ∼5000 km diameter for corresponding azimuthally elongated patches with ∼100 km size in the ionosphere. Using a ray-tracing-based calculation of the divergence of chorus raypaths from a point source, together with the corresponding resonant energies, we found that the chorus patch size is most probably not a result of ray divergence but a property of the wave excitation region.Citation: Nishimura, Y., et al. (2011), Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions,

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Ground-based observations of diffuse auroral structures in conjunction with Reimei measurements

Cited by 18 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

First optical observations of interhemispheric electron reflections within pulsating aurora

Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions

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