Purple Auroral Rays and Global Pc1 Pulsations Observed at the CIR‐Associated Solar Wind Density Enhancement on 21 March 2017

Shiokawa, K.; Ozaki, Mitsunori; Kadokura, Akira; Endo, Yoshinori; Sakanoi, Takeshi; Kurita, Satoshi; Oyama, Shin‐ichiro; Connors, Martin; Schofield, Ian; Ruohoniemi, J. M.; Nosé, M.; Nagatsuma, Tsutomu; Sakaguchi, Kaori; Otsuka, Yuichi; Пашинин, Александр; Рахматулин, Р. А.; Шевцов, Б. М.; Poddelsky, Igor; Engebretson, M. J.; Raita, Tero; Tanaka, Yoshimasa; Shinohara, Masanao; Teramoto, Masaaki; Nomura, Reiko; Fujimoto, Akiko; Matsuoka, A.; Higashio, Nana; Takashima, Takeshi; Shinohara, I.; Albert, J. M.

doi:10.1029/2018gl079103

Cited by 5 publications

(9 citation statements)

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“…It is interesting to note that the purple/blue aurora in the present event was observed during a weak geomagnetic storm that occurred in association with the arrival of a CIR. Similar purple/blue auroras associated with the CIR arrival were reported by Shiokawa et al (2018) based on a ground‐based observation at Husafell, Iceland. Shiokawa et al (2019) indicated based on statistical study of purple/blue emission from N 2 + ions at a wavelength of 427.8 nm measured by a photometer over 14 years at Athabasca, Canada, that the 427.8 nm emission exceeds 100 Rayleighs when solar wind speed and density is high.…”

Section: Discussionsupporting

confidence: 85%

Arase Observation of the Source Region of Auroral Arcs and Diffuse Auroras in the Inner Magnetosphere

et al. 2020

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Auroral arcs and diffuse auroras are common phenomena at high latitudes, though characteristics of their source plasma and fields have not been well understood. We report the first observation of fields and particles including their pitch‐angle distributions in the source region of auroral arcs and diffuse auroras, using data from the Arase satellite at L ~ 6.0–6.5. The auroral arcs appeared and expanded both poleward and equatorward at local midnight from ~0308 UT on 11 September 2018 at Nain (magnetic latitude: 66°), Canada, during the expansion phase of a substorm, while diffuse auroras covered the whole sky after 0348 UT. The top part of auroral arcs was characterized by purple/blue emissions. Bidirectional field‐aligned electrons with structured energy‐time spectra were observed in the source region of auroral arcs, while source electrons became isotropic and less structured in the diffuse auroral region afterwards. We suggest that structured bidirectional electrons at energies below a few keV were caused by upward field‐aligned potential differences (upward electric field along geomagnetic field) reaching high altitudes (~30,000 km) above Arase. The bidirectional electrons above a few keV were probably caused by Fermi acceleration associated with the observed field dipolarization. Strong electric‐field fluctuations and earthward Poynting flux were observed at the arc crossing and are probably also caused by the field dipolarization. The ions showed time‐pitch‐angle dispersion caused by mirror reflection. These results indicate a clear contrast between auroral arcs and diffuse auroras in terms of source plasma and fields and generation mechanisms of auroral arcs in the inner magnetosphere.

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Section: Discussionsupporting

confidence: 85%

Arase Observation of the Source Region of Auroral Arcs and Diffuse Auroras in the Inner Magnetosphere

et al. 2020

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“…Such EMIC waves propagate along the field lines and are often observed as Pc 1 pulsations on the ground. The EMIC waves and the Pc 1 pulsations shown in this paper have already been analyzed by Shiokawa et al (). They showed that the Pc 1 pulsations with a similar dominant frequency were observed at subauroral latitudes over a wide local time range from midnight to afternoon sectors (cf.…”

Section: Discussionsupporting

confidence: 61%

Direct Comparison Between Magnetospheric Plasma Waves and Polar Mesosphere Winter Echoes in Both Hemispheres

et al. 2019

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We present the first and direct comparison between magnetospheric plasma waves and polar mesosphere winter echoes (PMWE) simultaneously observed by the conjugate observation with Arase satellite and high-power atmospheric radars in both hemispheres, namely, the Program of the Antarctic Syowa Mesosphere, Stratosphere, and Troposphere/Incoherent Scatter Radar at Syowa Station (SYO; −69.00°S, 39.58°E), Antarctica, and the Middle Atmosphere Alomar Radar System at Andøya (AND; 69.30°N, 16.04°E), Norway. The PMWE were observed during 03-07 UT on 21 March 2017, just after the arrival of corotating interaction region in front of high-speed solar wind stream. An isolated substorm occurred at 04 UT during this interval. Electromagnetic ion cyclotron (EMIC) waves and whistler mode chorus waves were simultaneously observed near the magnetic equator and showed similar temporal variations to that of the PMWE. These results indicate that chorus waves as well as EMIC waves are drivers of precipitation of energetic electrons, including relativistic electrons, which make PMWE detectable at 55-to 80-km altitude. Cosmic noise absorption measured with a 38.2-MHz imaging riometer and low-altitude echoes at 55-70 km measured with an medium-frequency radar at SYO also support the relativistic electron precipitation. We suggest a possible scenario in which the various phenomena observed in near-Earth space, such as magnetospheric plasma waves (EMIC waves and chorus waves), pulsating auroras, cosmic noise absorption, and PMWE, can be explained by the interaction between the high-speed solar wind containing corotating interaction regions and the magnetosphere.

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“…Thus, 427.8-nm emission of more than 100 R is almost always observed at subauroral latitudes during these high geomagnetic activity times. Shiokawa et al (2018) reported impressive purple auroral rays observed at the arrival of a CIR in the solar wind. In order to investigate response of strong 427.8-nm emissions to such particular characteristics of solar wind and geomagnetic field variations, we made a superposed epoch analysis of solar wind and geomagnetic activity parameters with an epoch time when I 4278 exceeds 100 R. Figure 8 It is interesting to note that the timing that I 4278 becomes more than 100 R is characterized by an increase of solar wind speed and a decrease of the solar wind density for both sunlit and dark ionosphere.…”

Section: 1029/2019ja026704mentioning

confidence: 99%

“…Thus, 427.8-nm emission of more than 100 R is almost always observed at subauroral latitudes during these high geomagnetic activity times. Shiokawa et al (2018) reported impressive purple auroral rays observed at the arrival of a CIR in the solar wind. In order to investigate response of strong 427.8-nm emissions to such particular characteristics of solar wind and geomagnetic field variations, we made a superposed epoch analysis of solar wind and geomagnetic activity parameters with an epoch time when I 4278 exceeds 100 R. Figure 8 shows the result of a superposed epoch analysis for the solar wind parameters (IMF-Bz, and solar wind pressure, speed, and density) and geomagnetic indices (SYM-H and AE indices) over ±3 days relative to the epoch time when the 427.8-nm intensity first exceeded 100 R at the zenith of Athabasca, Canada, for θ s > −24°(a-f) and θ s < −24°(g-l).…”

Section: 1029/2019ja026704mentioning

confidence: 99%

“…Gerrard et al (2010) reported photometric observation of the 427.8-nm emission observed at South Pole and McMurdo in the auroral zone over 3 years of 2003-2005 to show their temporal variations from minutes to hourly timescales. Recently, Shiokawa et al (2018) showed the appearance of purple auroral rays in the upper part of discrete aurora under sunlit conditions in Iceland, associated with the arrival of a corotating interaction region (CIR) of the solar wind. However, statistical characteristics of this N 2 + (1NG) emission in relation to the solar wind parameters have not been investigated yet.…”

Section: Introductionmentioning

confidence: 99%

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Statistical Study of Auroral/Resonant‐Scattering 427.8‐nm Emission Observed at Subauroral Latitudes Over 14 Years

2019

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Auroral emission at 427.8-nm from N 2 + ions is caused by precipitation of energetic electrons, or by resonant scattering of sunlight by auroral N 2 + ions. The latter often causes impressive purple aurora at high altitudes. However, statistical characteristics of auroral 427.8-nm emission have not been well studied. In this paper we report occurrence characteristics of high 427.8-nm emission intensities (more than 100 R) at subauroral latitudes, based on measurements by a filter-tilting photometer over 14 years (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018) at Athabasca, Canada (magnetic latitude:~62°). We divided the data set into solar elevation angles (θ s ) more than and less than −24°(shadow height of sunlight: 600 km) to separate the 427.8-nm emissions caused by resonant scattering of sunlight and those excited by auroral electrons, respectively. The occurrence rate of 427.8-nm emissions of more than 100 R is 10.6% and 7.65% for θ s more than and less than −24°, respectively, confirming that resonant scattering of sunlight by N 2 + ions is a cause of the strong 427.8-nm emissions of more than 100 R in the sunlit ionosphere. The occurrence rate is high in the postmidnight sector and increases with increasing geomagnetic activity, solar wind speed, and density. The occurrence rate is lowest in winter. A high occurrence rate was observed in 2015-2018, during the declining phase of the 11-year solar activity. Superposed epoch analysis indicates that the 427.8-nm emission exceeds 100 R when solar wind speed increases and solar wind density concurrently decreases, though the standard deviation of the data is rather large.Plain Language Summary Purple auroras can be caused either by energetic electrons at low altitudes (about 100 km), or by scattering of sunlight at much higher altitudes where the auroral curtains are in the Sun although the ground is in darkness. We have studied both types by sorting measurements of the purple emission from ionized nitrogen molecules depending on how far the Sun is below the horizon. We used 14 years' worth of data in order to study the effects over more than a solar cycle (11 years typically). The emission is stronger when general auroral activity increases, which is in turn related to solar wind speed and density. Same result was obtained by binning solar wind and geomagnetic activity data, timing them relative to strong purple aurora. It is also highest in the declining phase of the solar cycle. The emission intensity becomes low in winter. Recently, a type of purple aurora outside of the normal auroral oval has been reported, called "STEVE." We note that we have studied the "traditional" type of purple aurora.

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Purple Auroral Rays and Global Pc1 Pulsations Observed at the CIR‐Associated Solar Wind Density Enhancement on 21 March 2017

Cited by 5 publications

References 46 publications

Arase Observation of the Source Region of Auroral Arcs and Diffuse Auroras in the Inner Magnetosphere

Arase Observation of the Source Region of Auroral Arcs and Diffuse Auroras in the Inner Magnetosphere

Direct Comparison Between Magnetospheric Plasma Waves and Polar Mesosphere Winter Echoes in Both Hemispheres

Statistical Study of Auroral/Resonant‐Scattering 427.8‐nm Emission Observed at Subauroral Latitudes Over 14 Years

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