Effective lifetime of O(<sup>1</sup><i>S</i>) in pulsating aurora

Scourfield, M. W. J.; Parsons, N. R.; Dennis, L. P.; Innes, W.F.

doi:10.1029/ja076i016p03692

Cited by 17 publications

(13 citation statements)

References 14 publications

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“…We are however investigating sharp‐edged fluctuating patches. So if the observations by Scourfield et al () can be generalized, the high values of mean effective lifetime of the O( 1 S) excitation can indicate that we capture most of the fluctuating precipitation.…”

Section: Discussionmentioning

confidence: 90%

“…Its green‐light is the brightest line in the visible spectrum in most auroras, and also for fluctuating aurora. It is however limited by a mean effective lifetime of 0.3 to 0.59 s of the O( 1 S) excitation, the highest values found in observations of sharp‐edged fluctuating patches (Scourfield et al, ). This is due to the ∼0.75 s lifetime of the direct O( 1 S) excitation, quenching of the excited state below 100 km and additional indirect excitation processes (e.g., Brekke, ).…”

Section: Discussionmentioning

confidence: 97%

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On the Persistent Shape and Coherence of Pulsating Auroral Patches

et al. 2018

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The pulsating aurora covers a broad range of fluctuating shapes that are poorly characterized.The purpose of this paper is therefore to provide objective and quantitative measures of the extent to which pulsating auroral patches maintain their shape, drift and fluctuate in a coherent fashion. We present results from a careful analysis of pulsating auroral patches using all-sky cameras. We have identified four well-defined individual patches that we follow in the patch frame of reference. In this way we avoid the space-time ambiguity which complicates rocket and satellite measurements. We find that the shape of the patches is remarkably persistent with 85-100% of the patch being repeated for 4.5-8.5 min. Each of the three largest patches has a temporal correlation with a negative dependence on distance, and thus does not fluctuate in a coherent fashion. A time-delayed response within the patches indicates that the so-called streaming mode might explain the incoherency. The patches appear to drift differently from the SuperDARN-determined ⃗ E × ⃗ B convection velocity. However, in a nonrotating reference frame the patches drift with 230-287 m/s in a north eastward direction, which is what typically could be expected for the convection return flow.

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Section: Discussionmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 97%

On the Persistent Shape and Coherence of Pulsating Auroral Patches

et al. 2018

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“…The growth time of an FB twostream instability is much shorter (less than 1 s (K. Schlegel, private communication, 1996)) than the delays in variations observed. Furthermore, auroral images including the • 557.7nm auroral emission has a theoretical lifetime of 0.74 s and effective lifetimes at 100 km of 0.3 to 0.59 s [Scourfield et al, 1971]. Delays in absorption of up to 60 s in a particular direction in space cannot therefore be of ionospheric origin.…”

Section: Auroral Eventsmentioning

confidence: 99%

Cosmic radio noise absorption related to structures in auroral luminosity

Stoker¹,

Mathews²,

Scourfield³

1997

J. Geophys. Res.

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Abstract. Digitized all-sky white light images of auroral optical emissions, recorded by a low-light level TV system at Sanae (70.3øS, 2.4øW, L = 4.0), have been mapped onto the angular sensitivity functions of the inner four beams of a 16-element imaging riometer. Cosmic radio waves of 5-10 m wavelengths appeared to be absorbed more strongly in directions through regions adjacent to discrete auroral arcs than through the arc regions themselves. These stronger absorptions may be due either to enhanced electron temperatures, caused by the Farley-Buneman two-stream instability in the presence of large electric fields around auroral arcs in the E region, or to D region absorption caused by energetic electrons precipitating along magnetic field lines passing through regions adjacent to auroral arcs. The two auroral events before local magnetic midmght reported in this paper started with high luminosity and small ionosphehc absorption. The absorption increased as the event developed. Auroral luminosities and structures were changing in all four viewing directions during the event on May 10, 1992, with variations in absorptions following variations in luminosity after a delay of 30 s. The event on June 8, 1992, involved a pulsating arc structure. Changes in absorption appeared to be delayed relative to changes in luminosity that varied from 0 to 60 s in a particular viewing direction. The auroral event after local magnetic mi•ght on April 14, 1993, differed from the former two events in the appearance of pulsating auroral patches and in slower temporal variations, but, occasionally, changes in absorption of cosmic radio noise in the four beam directions were still delayed relative to changes in luminosity. The observed spatial and temporal differences in regions of optical emissions and ionospheric absorption should be of magnetospheric origin rather than ionospheric origin on account of the long delay times.

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“…Furthermore, time lag between 427.8 and 557.7 nm emissions can be used for derivation of change of molecular oxygen (cf. Scourfield et al 1971), while time delay of 630 nm can be used for derivation of change of atomic oxygen (cf. Kalogerakis et al 2009).…”

Section: Choice Of Five Wavelengthsmentioning

confidence: 99%

“…Turunen et al 2009;Isono et al 2014). Photometric observations can be used to infer an average energy of the precipitating electrons, which leads to derivation of ionospheric conductivities, and deviation in the atmospheric composition induced by auroral heating (e.g., Gustavsson et al 2001;Hecht et al 1989Hecht et al , 1999; Robinson and Vondrak 1994;Vallance Jones and Gattinger 1990;Scourfield et al 1971). The altitude of the lower border and the altitude of maximum emission depend strongly on the highest and typical energy levels of the precipitating electrons (Gustavsson et al 2001).…”

Section: Introductionmentioning

confidence: 99%

A new five-wavelength photometer operated in Tromsø (69.6°N, 19.2°E)

Nozawa

Kawabata

Hosokawa

et al. 2018

Earth Planets Space

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A new five-wavelength photometer was developed and installed at the EISCAT Tromsø site (69.6°N, 19.2°E) in January 2017. The photometer consists of two units: an optical unit and a control unit together with a PC. The photometer is capable of simultaneously observing auroral emissions with five wavelengths. A uniqueness of the present system is its capability of precise pointing, which enables pointing the photometer at the field-aligned position using a star image obtained with a coaxial digital camera. Another uniqueness of the system is its capability of taking data at a sampling rate of 400 Hz. Some preliminary results including correlations between 427.8 nm and 557.7 nm, 630 nm, 777.4 nm, and 844.6 nm are presented. These comparisons are not significant unless all of the five wavelength emissions emanated from exactly the same volume (i.e., magnetic zenith) in the ionosphere, which the present system has.

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Effective lifetime of O(¹S) in pulsating aurora

Cited by 17 publications

References 14 publications

On the Persistent Shape and Coherence of Pulsating Auroral Patches

On the Persistent Shape and Coherence of Pulsating Auroral Patches

Cosmic radio noise absorption related to structures in auroral luminosity

A new five-wavelength photometer operated in Tromsø (69.6°N, 19.2°E)

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Effective lifetime of O(1S) in pulsating aurora

Cited by 17 publications

References 14 publications

On the Persistent Shape and Coherence of Pulsating Auroral Patches

On the Persistent Shape and Coherence of Pulsating Auroral Patches

Cosmic radio noise absorption related to structures in auroral luminosity

A new five-wavelength photometer operated in Tromsø (69.6°N, 19.2°E)

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Product

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Effective lifetime of O(¹S) in pulsating aurora