Diffuse and Pulsating Aurora

Nishimura, Y.; Lessard, M.; Katoh, Yutai; Miyoshi, Yoshizumi; Grono, Eric; Partamies, Noora; Sivadas, Nithin; Hosokawa, K.; Fukizawa, Mizuki; Samara, M.; Michell, R.; Kataoka, Ryuho; Sakanoi, Takeshi; Whiter, Daniel; Oyama, S.; Ogawa, Y.; Kurita, Satoshi

doi:10.1007/s11214-019-0629-3

Cited by 91 publications

(104 citation statements)

References 203 publications

(286 reference statements)

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“…A recent study by Hosokawa and Ogawa (2015) showed a higher European Incoherent Scatter (EISCAT) electron density at lower altitudes during PsA, which is more pronounced in the morning sector. Similarly, Oyama et al (2016) showed a maximum electron density below 100 km during a pulsating aurora. Jones et al (2009) utilized ionization from incoherent scatter radar in Poker Flat, Alaska, to estimate the energy distribution of PsA electrons and compared it with rocket measurements.…”

Section: Introductionmentioning

confidence: 88%

Observations of precipitation energies during different types of pulsating aurora

et al. 2020

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Abstract. Pulsating aurora (PsA) is a diffuse type of aurora with different structures switching on and off with a period of a few seconds. It is often associated with energetic electron precipitation (>10 keV) resulting in the interaction between magnetospheric electrons and electromagnetic waves in the magnetosphere. Recent studies categorize pulsating aurora into three different types – amorphous pulsating aurora (APA), patchy pulsating aurora (PPA), and patchy aurora (PA) – based on the spatial extent of pulsations and structural stability. Differences in precipitation energies of electrons associated with these types of pulsating aurora have been suggested. In this study, we further examine these three types of pulsating aurora using electron density measurements from the European Incoherent Scatter (EISCAT) VHF/UHF radar experiments and Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) cosmic noise absorption (CNA) measurements. Based on ground-based all-sky camera images over the Fennoscandian region, we identified a total of 92 PsA events in the years between 2010 and 2020 with simultaneous EISCAT experiments. Among these events, 39, 35, and 18 were APA, PPA, and PA types with a collective duration of 58, 43, and 21 h, respectively. We found that, below 100 km, electron density enhancements during PPAs and PAs are significantly higher than during APA. However, there are no appreciable electron density differences between PPA and APA above 100 km, while PA showed weaker ionization. The altitude of the maximum electron density also showed considerable differences among the three types, centered around 110, 105, and 105 km for APA, PPA, and PA, respectively. The KAIRA CNA values also showed higher values on average during PPA (0.33 dB) compared to PA (0.23 dB) and especially APA (0.17 dB). In general, this suggests that the precipitating electrons responsible for APA have a lower energy range compared to PPA and PA types. Among the three categories, the magnitude of the maximum electron density shows higher values at lower altitudes and in the late magnetic local time (MLT) sector (after 5 MLT) during PPA than during PA or APA. We also found significant ionization down to 70 km during PPA and PA, which corresponds to ∼200 keV of precipitating electrons.

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Section: Introductionmentioning

confidence: 88%

Observations of precipitation energies during different types of pulsating aurora

et al. 2020

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“…Pulsating auroras (PsAs) are caused by the intermittent precipitation of electrons with energies ranging from a few kiloelectron volts to ~100 keV from the magnetosphere to the upper atmosphere (e.g., Miyoshi et al, 2010; Sandahl et al, 1980; Yau et al, 1981). Lower‐band chorus (LBC) waves cause the precipitation of these electrons through pitch angle scattering (e.g., Jaynes et al, 2013; Jones et al, 2009; Kasahara et al, 2018; Lessard, 2012; Miyoshi et al, 2010; Nishimura et al, 2010, 2020). Miyoshi, Saito et al (2015) have proposed a model to describe the relationship between the energy spectrum of the precipitating electrons in PsA and the frequency spectrum of LBC.…”

Section: Introductionmentioning

confidence: 99%

Relativistic Electron Microbursts as High‐Energy Tail of Pulsating Aurora Electrons

Miyoshi

Saito

Kurita

et al. 2020

Geophysical Research Letters

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In this study, by simulating the wave-particle interactions, we show that subrelativistic/ relativistic electron microbursts form the high-energy tail of pulsating aurora (PsA). Whistler-mode chorus waves that propagate along the magnetic field lines at high latitudes cause precipitation bursts of electrons with a wide energy range from a few kiloelectron volts (PsA) to several megaelectron volts (relativistic microbursts). The rising tone elements of chorus waves cause individual microbursts of subrelativistic/relativistic electrons and the internal modulation of PsA with a frequency of a few hertz. The chorus bursts for a few seconds cause the microburst trains of subrelativistic/relativistic electrons and the main pulsations of PsA. Our simulation studies demonstrate that both PsA and relativistic electron microbursts originate simultaneously from pitch angle scattering by chorus wave-particle interactions along the field line. Plain Language Summary Pulsating aurora electron and relativistic electron microbursts are precipitation bursts of electrons from the magnetosphere to the thermosphere and the mesosphere with energies ranging from a few kiloelectron volts to tens of kiloelectron volts and subrelativistic/relativistic, respectively. Our computer simulation shows that pulsating aurora electron (low energy) and relativistic electron microbursts (relativistic energy) are the same product of chorus wave-particle interactions, and relativistic electron microbursts are high-energy tail of pulsating aurora electrons. The relativistic electron microbursts contribute to significant loss of the outer belt electrons, and our results suggest that the pulsating aurora activity can be often used as a proxy of the radiation belt flux variations.

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“…The diffuse aurora is a frequent source of high‐energy precipitating electron and is the dominant source of total auroral energy flux (Newell et al, 2009; Nishimura et al, 2020). Consisting of higher energy particles than its counterpart, the discrete aurora, the diffuse aurora is largely observed in the equatorward portion of the auroral oval (Nishimura et al, 2020). The nightside diffuse aurora is strongest in the early morning sector, with the region of strongest energy flux centered on 3 h magnetic local time (MLT) (Newell et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…In addition to EUV photoionization, both Pedersen and Hall conductivities also receive contributions from precipitating electrons (Vickrey et al, 1981). However, in the E region ionosphere, Hall conductivity peaks at a lower altitude than Pedersen conductivity, making Hall conductance more susceptible to deeply penetrating precipitating electrons and thus to higher energy electrons (Coumans et al, 2004; Nishimura et al, 2020). In fact, when considering high‐latitude Hall conductance, auroral precipitation has a greater impact than EUV photoionization (Lotko et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Observational Evidence for the Role of Hall Conductance in Alfvén Wave Reflection

et al. 2020

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Electromagnetic energy carried by magnetohydrodynamic modes is an important mechanism in the energy transfer between the magnetosphere and the ionosphere. Alfvén waves are known to carry field-aligned currents and thus play an important role in the dynamics of the ionosphere-magnetosphere coupling. The role of Hall conductance in this interplay has been explored in magnetohydrodynamic models of the ionosphere but has hitherto not been observed in situ. We use 5 years of observations from the Swarm mission to shed light on this interplay. We present a high-latitude climatology of both the measured Poynting flux and the measured Alfvén wave reflection coefficient. Our results indicate that high-energy precipitation, which penetrates deep into the ionosphere and directly leads to strongly enhanced Hall conductance, is an important cause of positively interfering Alfvén wave reflection. We present such observational evidence and, with that, suggest that Hall conductance is substantially more important in the ionospheric wave reflection climatology than hitherto believed.

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Diffuse and Pulsating Aurora

Cited by 91 publications

References 203 publications

Observations of precipitation energies during different types of pulsating aurora

Observations of precipitation energies during different types of pulsating aurora

Relativistic Electron Microbursts as High‐Energy Tail of Pulsating Aurora Electrons

Observational Evidence for the Role of Hall Conductance in Alfvén Wave Reflection

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