Thermally excited 630.0 nm O(<sup>1</sup><i>D</i>) emission in the cusp: A frequent high‐altitude transient signature

Carlson, H. C.; Oksavik, K.; Moen, J.

doi:10.1002/jgra.50516

Cited by 10 publications

(42 citation statements)

References 43 publications

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“…In agreement with earlier studies, the thermal component was significant when the electron temperature exceeded 3000 K with electron density enhancements between (1–5) × 10 11 m −3 [ Egeland et al , ]. In agreement with earlier studies [ Carlson et al , ; Johnsen et al , ; Kozyra et al , ; Egeland et al , ], our estimated emission altitude for the thermal component is higher than the generally accepted emission altitude of 225–250 km for the 630.0 nm emission [ Lockwood et al , ]. Our findings agree with Egeland et al [] that the thermal excitation may be responsible for the 630.0 nm emission at 350 km and above.…”

Section: Discussionsupporting

confidence: 93%

“…Theoretically, Kozyra et al [] suggested that the emission altitude for the thermal component should be expected near 500 km which is higher than the estimated peak emission altitudes for the events studied here. However, the peak emission altitude for the event on 22 January 2012 is closer to 400–450 km reported by Carlson et al []. The estimated peak emission altitudes for both events studied in our work are in agreement with thermal component emission peak near 350 km reported by Wickwar and Kofman [].…”

Section: Discussionsupporting

confidence: 92%

“…It is important to point out that the ESR 42 m data were checked for the whole dayside, but the thermal component only became significant when the cusp was over Svalbard. In the scanning experiment used by Carlson et al [], thermally excited 630.0 nm emissions were also detected in the cusp sector. We note that we were limited to the winter period due to optical observations, but such events may in principal also exist in other seasons.…”

Section: Discussionmentioning

confidence: 99%

“…The thermal excitation component depends on the electron density ( N e ) and the number density of atomic oxygen ( N o ) which are available to excite by collision, hence the excitation rate α ( T e ). Carlson et al [] employed equation and derived the altitude ( h ) discriminated volume emission rate per kilometer (Rayleighs/km) of emission at 630.0 nm:

I_{630} (h) = α ([], T_{e} (h)) \times N_{o} (h) \times N_{e} (h) (normal Rayleighs / km)

which when integrated over the line of sight gives the total vertical column intensity for the emission at 630.0 nm:

I_{630} = \int_{250 normalkm}^{650 normalkm} I_{630} (h) normald h (normalRayleighs)

where N o ( h ) and N e ( h ) are measured in cm −3 , T e ( h ) in kelvin, and all variables are functions of altitude ( h ) in kilometers. For more details, see Carlson et al [, and references therein].…”

Section: Instrumentationmentioning

confidence: 99%

“…A combination of the electron temperature exceeding 3000 K and an electron density enhancement would indicate poor thermal balance. In such cases another cooling mechanism, collisional excitation of the O( 1 D) state, which can lead to 630.0 nm emissions, becomes important [ Carlson et al , ].…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionsupporting

confidence: 93%

Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 99%

I_{630} (h) = α ([], T_{e} (h)) \times N_{o} (h) \times N_{e} (h) (normal Rayleighs / km)

which when integrated over the line of sight gives the total vertical column intensity for the emission at 630.0 nm:

I_{630} = \int_{250 normalkm}^{650 normalkm} I_{630} (h) normald h (normalRayleighs)

Section: Instrumentationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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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Dynamic properties of throat aurora revealed by simultaneous ground and satellite observations

et al. 2017

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Throat aurora is defined as south‐north aligned auroral arcs equatorward of the dayside cusp aurora and was suggested to be the results of cold magnetospheric plasma interaction with magnetopause reconnection, but its observational properties have not yet been well established. In this paper we carefully examine a sequence of throat auroras observed over Svalbard on 27 December 2003. Observations from 630.0 nm [OI] show that poleward moving throat auroras frequently show brightening followed by dimming in auroral intensity, and sometimes, the brightening throat aurora is a precursor of poleward moving auroral forms. Simultaneous all‐sky images and HF radar backscatter observations along geomagnetic meridian show that the throat aurora brightening is drifting with ionospheric E × B convection and is colocated with enhanced spectral width poleward of the convection reversal boundary (CRB), while its dimming tends to be in the vicinity of the CRB. This leads us to propose that the throat aurora brightening and dimming may be on the open and closed field lines, respectively. Particle data from NOAA 16 confirm that the dimming throat aurora is associated with precipitation of magnetosheath‐like particles mixed with magnetospheric ions (>30 keV), which is characteristic of the low‐latitude boundary layer. For particle data from Defense Meteorological Satellite Program F16, we notice that the dimming throat aurora is associated with lower fluxes of magnetosheath‐like electrons accompanied with magnetospheric electrons, which is most likely on closed field lines. The dynamic properties of throat aurora presented in this paper are thus important to understand its generation mechanisms.

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Horizontal profile of a moving red line cusp aurora

et al. 2017

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Auroral emission at a wavelength of 630.0 nm (red line) has a long radiative time. In this study, we show how this long radiative time controls the horizontal extent of a moving mesoscale aurora, which is typical of the cusp. Using high time resolution (4 s) observations by an all‐sky imager at Longyearbyen, Svalbard, and observations by the European Incoherent Scatter Svalbard Radar (ESR), we examined the auroral emission enhancements obtained in the cusp during an interval of southward interplanetary magnetic field on 27 November 2011. Simultaneous observations from the all‐sky imager and the ESR clearly show the manner in which auroral emission regions passed through the radar's field of view. When the front edge of the moving auroral structure intersected the radar's field of view, the ESR electron temperature was enhanced. A few minutes later, the ESR electron temperature dropped to the background level, indicating that the mesoscale electron precipitation region shifted away from the radar's field of view. At that time, the auroral emission in the radar's field of view decreased but still had adequate intensities. These results provide evidence demonstrating that moving cusp auroral emission occurs behind the electron precipitation region as well as inside that region. We interpreted this feature semiquantitatively by using the equation of continuity of the density of the excited atomic oxygen. Our model indicates that the maximum intensity in the moving auroral structure occurs at a point along the trailing edge of the electron precipitation region and that the velocity of that region is important for determining how the 630.0 nm aurora emissions extend horizontally.

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Thermally excited 630.0 nm O(¹D) emission in the cusp: A frequent high‐altitude transient signature

Cited by 10 publications

References 43 publications

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

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

Dynamic properties of throat aurora revealed by simultaneous ground and satellite observations

Horizontal profile of a moving red line cusp aurora

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Thermally excited 630.0 nm O(1D) emission in the cusp: A frequent high‐altitude transient signature

Cited by 10 publications

References 43 publications

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

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

Dynamic properties of throat aurora revealed by simultaneous ground and satellite observations

Horizontal profile of a moving red line cusp aurora

Contact Info

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Thermally excited 630.0 nm O(¹D) emission in the cusp: A frequent high‐altitude transient signature