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

Liang, J.; Yang, B.; Donovan, E.; Burchill, J. K.; Knudsen, D. J.

doi:10.1002/2017ja024127

Cited by 13 publications

(20 citation statements)

References 71 publications

(165 reference statements)

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“…The existence of the red‐line component is expected and relatively well understood, given the established conjunction between STEVE and strong electron heating in the upper F region ionosphere (MacDonald et al, ). The electron heating is led by the magnetospheric heat flux and thermal conduction in the upper ionosphere (Liang et al, ). With elevated electron temperature, a portion of the higher‐energy tail of the thermal distribution of ionospheric electrons may exceed the threshold level for O( 1 D) excitation (~2 eV), leading to the so‐called “thermal emission” of red‐line.…”

Section: Discussionmentioning

confidence: 99%

First Observations From the TREx Spectrograph: The Optical Spectrum of STEVE and the Picket Fence Phenomena

Gillies

Donovan

Hampton

et al. 2019

Geophysical Research Letters

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128

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We present the first observations of ionospheric phenomena using the newly deployed Transition Region Explorer (TREx) Spectrograph. On the night of 10 April 2018, STEVE (Strong Thermal Emission Velocity Enhancement) and the Picket Fence optical structures were observed by the spectrograph in Lucky Lake, Saskatchewan. STEVE contains an enhancement of the OI red‐line (630‐nm) emission and a continuum which spans the visible wavelengths. Based upon its spectrum, we assert that the characteristic mauve color of STEVE is a result of this continuum. The spectrum of the Picket Fence contains a strong OI green‐line (557.7‐nm) emission similar to that produced in typical auroral structures. From their spectra, we assert that the Picket Fence is caused by particle precipitation and thus that the Picket Fence is a form of aurora, while STEVE's spectrum confirms that it is not aurora.

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Section: Discussionmentioning

confidence: 99%

First Observations From the TREx Spectrograph: The Optical Spectrum of STEVE and the Picket Fence Phenomena

Gillies

Donovan

Hampton

et al. 2019

Geophysical Research Letters

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128

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“…To evaluate and compare the typical optical brightness of the Alfvénic aurora and the energetic inverted‐V precipitation, we resort to the auroral transport model developed in Liang et al (, ). For the STEB precipitation, we assume a differential energy flux of 1 × 10 9 eV/cm 2 /s/sr/eV in the energy range 10–300 eV and within 15° pitch angle at 3,000‐km altitude.…”

Section: Introductionmentioning

confidence: 99%

“…For the inverted‐V arc, we assume a monoenergetic isotropic precipitation with core energy of 6 keV and total energy flux of 10 erg/cm 2 /s. We use the Liang et al (, ) model to compute the intensity of three major auroral emission lines, 427.8, 557.7, and 630 nm, within the band‐pass range of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) white light camera (400–700 nm). The input parameters for the run come from the Fort Smith Geographic coordinates and realistic F 10.7 / Ap index on 18 March 2015 6 UT, the actual event time in this study.…”

Section: Introductionmentioning

confidence: 99%

e‐POP and Red Line Optical Observations of Alfvénic Auroras

et al. 2019

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Suprathermal electron bursts (STEBs), characterized by a board energy spectrum and a field-aligned pitch angle distribution, have been well recognized to be associated with electron acceleration by inertial Alfvén waves and are thus conventionally termed as "Alfvénic aurora." In this study, we report joint Enhanced-Polar-Outflow-Probe (e-POP) and ground-based optical observations of Alfvénic auroras. In particular, we highlight the prominence of 630-nm red line emissions under low-energy Alfvénic auroral precipitation. During the event interval, e-POP traverses two arcs. One bright arc dominated by green line emissions is clearly seen by all optical instruments; it is embedded in upward field-aligned currents (FACs) yet leaves little imprint on the e-POP suprathermal electron imager (SEI), likely due to that the precipitation is well above the upper energy limit of SEI. On the other hand, there is a red line arc that is pronounced only in 630-nm images. Such a red-line-only arc is located in a transition from large-scale upward FACs to downward FACs and is associated with a prominent STEB structure detected by e-POP SEI. The STEB features an inverse energy time dispersion, namely, that lower-energy electrons are seen earlier while higher-energy electrons appear later. The red-line-only arc and its separation from the green line arc evolve in a repeatable fashion, each stemming from a poleward auroral intensification (PAI) propagated from higher latitudes. Following each poleward auroral intensification the green line arc progressively moved southward, while the red-line-only arc is quasi-stationary and stayed relatively stable in latitude. We propose tentative interpretations of the above features based upon stationary inertial Alfvén waves.

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“…Pulsating auroras do not exhibit a particularly strong optical luminosity, hinting at a limited energy flux of the precipitation (Royrvik & Davis, ). The FAC intensity within pulsating auroral patches was also found to be moderate only, with peak magnitude of at most a couple of μA/m 2 (Gillies et al, ; Liang et al, , hereafter referred to as LJ17).…”

Section: Introductionmentioning

confidence: 99%

Ionospheric Electron Heating Associated With Pulsating Auroras: Joint Optical and PFISR Observations

et al. 2018

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In a recent study, Liang et al. (2017, https://doi.org/10.1002/2017JA024127) repeatedly identified strong electron temperature (T e ) enhancements when Swarm satellites traversed pulsating auroral patches. In this study, we use joint optical and Poker Flat Incoherent Scatter Radar (PFISR) observations to further investigate the F region plasma signatures related to pulsating auroras. On 19 March 2015 night, which contained multiple intervals of pulsating auroral activities, we identify a statistical trend, albeit not a one-to-one correspondence, of strong T e enhancements (~500-1000 K) in the upper F region ionosphere during the passages of pulsating auroras over PFISR. On the other hand, there is no discernible and repeatable density enhancement in the upper F region during pulsating auroral intervals. Collocated optical and NOAA satellite observations suggest that the pulsating auroras are composed of energetic electron precipitation with characteristic energy >10 keV, which is inefficient in electron heating in the upper F region. Based upon PFISR observations and simulations from Liang et al. (2017) model, we propose that thermal conduction from the topside ionosphere, which is heated by precipitating low-energy electrons, offers the most likely explanation for the observed electron heating in the upper F region associated with pulsating auroras. Such a heating mechanism is similar to that underlying the "stable auroral red arcs" in the subauroral ionosphere. Our proposal conforms to the notion on the coexistence of an enhanced cold plasma population and the energetic electron precipitation, in magnetospheric flux tubes threading the pulsating auroral patch. In addition, we find a trend of enhanced ion upflows during pulsating auroral intervals.On the other hand, if the downgoing magnetospheric electrons include a component of substantially "colder" electrons, for example, on order of~10 eV or less, electron heating in the upper ionosphere may operate in a fundamentally different way. The "cold" magnetospheric electrons cannot penetrate deeply into the ionosphere, but can strongly heat electrons near the topside boundary of the ionosphere. The heat will be conducted toward lower altitudes into the F region ionosphere. In this scenario, the T e enhancement seen in the F region ionosphere is a remote effect, meaning that the low-energy magnetospheric electrons do not actually penetrate to F region altitudes, so no significant ionization or red-line auroral excitation is LIANG ET AL. 4430

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

Cited by 13 publications

References 71 publications

First Observations From the TREx Spectrograph: The Optical Spectrum of STEVE and the Picket Fence Phenomena

First Observations From the TREx Spectrograph: The Optical Spectrum of STEVE and the Picket Fence Phenomena

e‐POP and Red Line Optical Observations of Alfvénic Auroras

Ionospheric Electron Heating Associated With Pulsating Auroras: Joint Optical and PFISR Observations

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