Faculty Profiles - SHIOKAWA, Kazuo

EMIC waves converted from equatorial noise due to M/Q=2 ions in the plasmasphere: Observations from Van Allen Probes and Arase Reviewed Open Access

Miyoshi, Y, S. Matsuda, S. Kurita, K. Nomura, K. Keika, M. Shoji, N. Kitamura, Y. Kasahara, A. Matsuoka, I. Shinohara, K. Shiokawa, S. Machida, O. Santolik, S. A. Boardsen, R. B. Horne, J. F. Wygant

Geophys. Res. Lett. Vol. 46 ( 11 ) page： 5662 - 5669 2019.6

Observations of low-latitude travelling ionospheric disturbances by a 630.0-nm airglow imager and the CHAMP satellite over Indonesia Reviewed International journal Open Access

A. C. Moral, K. Shiokawa, S. Suzuki, Huixin Liu, Y. Otsuka, C. Y. Yatini

J. Geophys. Res. Vol. 124 ( 3 ) page： 2198 - 2212 2019.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report the first comparison of ground and satellite measurements of low-latitude traveling ionospheric disturbances (TIDs). Three TID events were simultaneously observed by a 630.0-nm airglow imager and the CHAllenging Minisatellite Payload (CHAMP) satellite at Kototabang, Indonesia (geographic coordinates: 0.2 degrees S, 100.3 degrees E, geomagnetic latitude: 10.6 degrees S). In 630.0-nm airglow images of all three events, there are clear southward-moving structures. Events 1 and 2 are a single pulse with horizontal scales of similar to 500-1,000 km. Event 3 shows five wave fronts with a horizontal scale size of 500-1,000 km. All three TIDs are medium-scale TIDs. Horizontal wavelengths of both airglow intensity at an average emission altitude of 250 km and CHAMP neutral density variations measured at 400 km are estimated by fitting a sinusoidal function to the observed data. The estimated horizontal wavelengths for airglow and neutral density data are 1,031 and 880 km for event 1 and 560 and 420 km for event 3, respectively. These values between airglow and CHAMP are comparable, suggesting both instruments are observing the same wave. For event 1, the CHAMP electron density mapped along the geomagnetic field line onto the airglow altitude does not show wave structure similar to the airglow variation. For events 2 and 3, the plasma density did not show wavy structures similar to the waves seen in the airglow image and CHAMP neutral density. These results suggest that the TIDs observed in airglow images are not caused by ionospheric plasma instability but by gravity waves in the thermosphere.

DOI： 10.1029/2018JA025634

Comprehensive Study of Low-Latitude Pi2 Pulsations Using Observations From Multisatellite Swarm Mission and Global Network of Ground Observatories Reviewed Open Access

Neethal Thomas, Kazuo Shiokawa, Geeta Vichare

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 3 ) page： 1966 - 1991 2019.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

To understand the spatial features of low-latitude Pi2 (6.6-25 mHz) pulsations, a comprehensive study is carried out for the first time using magnetic field measurements from a global network of low-latitude ground stations (Mlat: +/- 2 degrees - 51 degrees) and the Swarm multisatellites located simultaneously at day and night local times. We have investigated 1-year data from 2014 and found 15 Pi2 events with coherent oscillations at satellite and ground. The Pi2 oscillations in the compressional, toroidal, and poloidal components at satellite and H, D, and Z components at ground are investigated by estimating its coherence, amplitude, and cross phase with respect to midnight ground H variations. The analogous pairs of magnetic field components (satellite compressional with ground H and satellite toroidal with ground D) above and below the ionosphere are found to have identical phase during night and opposite phase during day, indicating the magnetospheric and ionospheric sources for nighttime and daytime Pi2s, respectively. During nighttime, Pi2 oscillations identified in the poloidal component are found to oscillate in phase (out of phase) in the Southern (Northern) Hemisphere. At ground, the phase and amplitude of H showed significant change near the dawn terminator, whereas H oscillates mostly in phase with respect to midnight ground H at other local times. The oscillations in D component have phase reversal near midnight, dawn, dusk, and noon meridians with opposite hemispheres having opposite phase. These Pi2 characteristics observed globally at ground and at the topside ionosphere suggest that the sources for nighttime and daytime low-latitude Pi2s are oscillating field-aligned currents and ionospheric currents, respectively.

DOI： 10.1029/2018JA026094

Spatial Gradients in Geomagnetic Storm Time Currents Observed by Swarm Multispacecraft Mission Reviewed Open Access

Vichare Geeta, Thomas Neethal, Shiokawa Kazau, Bhaskar Ankush, Sinha Ashwini Kumar

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 2 ) page： 982 - 995 2019.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

This paper presents a comprehensive study of geomagnetic storm time currents using magnetic field recorded by multispacecraft polar-orbiting mission, Swarm. During geomagnetic storm period, the magnetic field variations obtained after removing the internal geomagnetic field and quiet time contributions can be considered as a proxy for storm time currents and are found to follow the temporal profile of Dst index very closely. These variations at the equatorial crossings recorded by multiple-spacecraft are used to estimate the Dst values and are found to have a good match with the ground-based Dst index. The average deviation between these two is around 4–13%. We have estimated the asymmetry by taking the difference between the magnetic field variations at two local time sectors separated by 12 hr. The estimated asymmetry shows a good match with the AsyH-index, especially when satellite traverses in the dawn-dusk sector. In general, the magnetic field variations are stronger in the night-to-dusk sector than day-to-dawn sector, which could be due to the larger pressure-gradients near night-to-dusk caused by ion movements. The important advantage of Swarm mission is that it provides an opportunity to investigate the longitudinal gradients in the storm time magnetic fields. It is observed that in general, the gradients are stronger during the main phase of the storm, centered near the equator with a latitudinal width of ~20–30° in both the hemispheres, and are supportive to the scenario of particle-injection from the magnetotail. The stronger gradients are observed at higher latitudes (~40°) during the episodes of substorms and might be associated with the ionospheric/field-aligned currents.

DOI： 10.1029/2018JA025692

Transient ionization of the mesosphere during auroral breakup: Arase satellite and ground-based conjugate observations at Syowa Station Reviewed Open Access

Ryuho Kataoka, Takanori Nishiyama, Yoshimasa Tanaka, Akira Kadokura, Herbert Akihito Uchida, Yusuke Ebihara, Mitsumu K. Ejiri, Yoshihiro Tomikawa, Masaki Tsutsumi, Kaoru Sato, Yoshizumi Miyoshi, Kazuo Shiokawa, Satoshi Kurita, Yoshiya Kasahara, Mitsunori Ozaki, Keisuke Hosokawa, Shoya Matsuda, Iku Shinohara, Takeshi Takashima, Tatsuhiko Sato, Takefumi Mitani, Tomoaki Hori, Nana Higashio

EARTH PLANETS AND SPACE Vol. 71 ( 1 ) page： 9 2019.1

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGEROPEN

Transient mesospheric echo in the VHF range was detected at an altitude of 65-70km during the auroral breakup that occurred from 2220 to 2226 UT on June 30, 2017. During this event, the footprint of the Arase satellite was located within the field of view of the all-sky imagers at Syowa Station in the Antarctic. Auroral observations at Syowa Station revealed the dominant precipitation of relatively soft electrons during the auroral breakup. A corresponding spike in cosmic noise absorption was also observed at Syowa Station, while the Arase satellite observed a flux enhancement of >100keV electrons and a broadband noise without detecting chorus waves or electromagnetic ion cyclotron waves. A general-purpose Monte Carlo particle transport simulation code was used to quantitatively evaluate the ionization in the middle atmosphere. Results of this study indicate that the precipitation of energetic electrons of >100keV, rather than X-rays from the auroral electrons, played a dominant role in the transient and deep (65-70km) mesospheric ionization during the observed auroral breakup.

DOI： 10.1186/s40623-019-0989-7

Visualization of rapid electron precipitation via chorus element wave-particle interactions Reviewed Open Access

Mitsunori Ozaki, Yoshizumi Miyoshi, Kazuo Shiokawa, Keisuke Hosokawa, Shin-ichiro Oyama, Ryuho Kataoka, Yusuke Ebihara, Yasunobu Ogawa, Yoshiya Kasahara, Satoshi Yagitani, Yasumasa Kasaba, Atsushi Kumamoto, Fuminori Tsuchiya, Shoya Matsuda, Yuto Katoh, Mitsuru Hikishima, Satoshi Kurita, Yuichi Otsuka, Robert C. Moore, Yoshimasa Tanaka, Masahito Nose, Tsutomu Nagatsuma, Nozomu Nishitani, Akira Kadokura, Martin Connors, Takumi Inoue, Ayako Matsuoka, Iku Shinohara

NATURE COMMUNICATIONS Vol. 10 ( 1 ) page： 257 2019.1

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Chorus waves, among the most intense electromagnetic emissions in the Earth's magnetosphere, magnetized planets, and laboratory plasmas, play an important role in the acceleration and loss of energetic electrons in the plasma universe through resonant interactions with electrons. However, the spatial evolution of the electron resonant interactions with electromagnetic waves remains poorly understood owing to imaging difficulties. Here we provide a compelling visualization of chorus element wave-particle interactions in the Earth's magnetosphere. Through in-situ measurements of chorus waveforms with the Arase satellite and transient auroral flashes from electron precipitation events as detected by 100-Hz video sampling from the ground, Earth's aurora becomes a display for the resonant interactions. Our observations capture an asymmetric spatial development, correlated strongly with the amplitude variation of discrete chorus elements. This finding is not theoretically predicted but helps in understanding the rapid scattering processes of energetic electrons near the Earth and other magnetized planets.

DOI： 10.1038/s41467-018-07996-z

PRELIMINARY RESULTS OF SIMULTANEOUS RECORDING OF AURORAL AND GEOMAGNETIC PULSATIONS AT THE ISTP SB RAS STATION ISTOK Reviewed Open Access

Beletskii A. B., Rakhmatulin R. A., Syrenova T. Ye, Vasilev R. V., Mikhalev A. V, Pashinin A. Yu, Shiokawa K., Nishitani N.

SOLAR-TERRESTRIAL PHYSICS Vol. 5 ( 2 ) page： 39 - 44 2019

Preliminary results of simultaneous recording of auroral and geomagnetic pulsations at the ISTP SB RAS station Istok Reviewed Open Access

Beletskii A.B., Rakhmatulin R.A., Syrenova T.Y., Vasilev R.V., Mikhalev A.V., Pashinin A.Y., Shiokawa K., Nishitani N.

Solnecno Zemnaa Fizika Vol. 5 ( 2 ) page： 43 - 48 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Solnecno Zemnaa Fizika

The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer. Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals. In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

DOI： 10.12737/szf-52201906

Spatiotemporal development of pulsating auroral patch associated with discrete chorus elements: Arase and PWING observations Reviewed

Ozaki M., Shiokawa K., Miyoshi Y., Hosokawa K., Oyama S., Yagitani S., Kasahara Y., Kasaba Y., Matsuda S., Kataoka R., Ebihara Y., Ogawa Y., Otsuka Y., Kurita S., Moore R. C., Tanaka Y. -M., Nose M., Nagatsuma T., Connors M., Nishitani N., Hikishima M., Kumamoto A., Tsuchiya F., Kadokura A., Nishiyama T., Inoue T., Imamura K., Matsuoka A., Shinohara I.

2019 URSI ASIA-PACIFIC RADIO SCIENCE CONFERENCE (AP-RASC) 2019

Temporal and Spatial Correspondence of Pc1/EMIC Waves and Relativistic Electron Precipitations Observed with Ground-Based Multi-Instruments on 27 March 2017 Reviewed Open Access

Hirai, A, F. Tsuchiya, T. Obara, Y. Kasaba, Y. Katoh, H. Misawa, K. Shiokawa, Y. Miyoshi, S. Kurita, S. Matsuda, M. Connors, T. Nagatsuma, K. Sakaguchi, Y. Kasahara, A. Kumamoto, A. Matsuoka, M. Shoji, I. Shinohara, J. M. Albert

Geophysical Research Letters Vol. 45 ( 24 ) page： 13182 - 13191 2018.12

Electrostatic Electron Cyclotron Harmonic Waves as a Candidate to Cause Pulsating Auroras Reviewed Open Access

M. Fukizawa, T. Sakanoi, Y. Miyoshi, K. Hosokawa, K. Shiokawa, Y. Katoh, Y. Kazama, A. Kumamoto, F. Tsuchiya, Y. Miyashita, Y. M. Tanaka, Y. Kasahara, M. Ozaki, A. Matsuoka, S. Matsuda, M. Hikishima, S. Oyama, Y. Ogawa, S. Kurita, R. Fujii

Geophysical Research Letters Vol. 45 ( 23 ) page： 12661 - 12668 2018.12

Language：English Publishing type：Research paper (scientific journal)

©2018. American Geophysical Union. All Rights Reserved. Pulsating auroras (PsAs) are thought to be generated by precipitating electrons scattered by lower-band chorus (LBC) waves near the magnetic equator. One-to-one correlation between the LBC intensity and the PsA intensity has been reported. Electrostatic electron cyclotron harmonic (ECH) waves can also scatter electrons. However, direct correlation between ECH and PsA has not been reported yet. In this study, using a coordinated Exploration of energization and Radiation in Geospace (Arase) satellite and ground-based imager observation, we report that not only LBC but also ECH have correlation with PsA. We estimated the precipitating electron energy by assuming that the time lag when the cross-correlation coefficient became the highest was travel time of electrons from the modulation region. We found that the estimated energies show reasonable values as the cyclotron resonance energy of each wave.

DOI： 10.1029/2018GL080145

Rapid Loss of Relativistic Electrons by EMIC Waves in the Outer Radiation Belt Observed by Arase, Van Allen Probes, and the PWING Ground Stations Open Access

Kurita S, Miyoshi Y, Shiokawa K, Higashio N, Mitani T, Takashima T, Matsuoka A, Shinohara I, Kletzing C. A, Blake J. B, Claudepierre S. G, Connors M, Oyama S, Nagatsuma T, Sakaguchi K, Baishev D, Otsuka Y

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 23 ) page： 12720 - 12729 2018.12

Large-Scale Ducting of Pc1 Pulsations Observed by Swarm Satellites and Multiple Ground Networks Reviewed Open Access

Hyangpyo Kim, Junga Hwang, Jaeheung Park, Yukinaga Miyashita, Kazuo Shiokawa, Ian R. Mann, Tero Raita, Jaejin Lee

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 23 ) page： 12703 - 12712 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Low Earth orbit satellites frequently encounter Pc1 pulsations, but most have been observed with limited latitudinal extent or short lifetime. In this study we analyze two large-scale Pc1 pulsations (both latitudinally wide and long-lasting) generated by ionospheric ducting effect using Swarm and ground magnetometers on 25 June and 3 September 2015. Swarm observed the 25 June pulsations on both dayside and nightside during the storm time substorm (a strong geomagnetic storm on 23 June with D-st = - 204 nT). We found the Pc1 pulsations were pervasive in both magnetic local time sectors of dayside and nightside for at least 2 hr. Another large Pc1 pulsation on 3 September was observed during a nonstorm substorm period. We conclude that (1) ionospheric ducting can transmit Pc1 waves to a wide range of L shells, (2) geomagnetic storm is not a prerequisite for such large-scale ducting, and (3) wave intensity can abruptly decrease across sharp gradients in the ionospheric plasma density.

DOI： 10.1029/2018GL080693

Energetic electron precipitation associated with pulsating aurora observed by VLF radio propagation during recovery phase of substorm on 27 March 2017 Reviewed Open Access

Tsuchiya,F, A. Hirai, T. Obara, H. Misawa, S. Kurita, Y. Miyoshi, K. Shiokawa, M. Connors, M. Ozaki, Y. Kasahara, A. Kumamoto, Y. Kasaba, A. Matsuoka, M. Shoji, I. Shinohara

Geophysical Research Letters Vol. 45 ( 23 ) page： 12651 - 12660 2018.12

The ARASE (ERG) magnetic field investigation Reviewed Open Access

Matsuoka A, Teramoto M, Nomura R, Nosé M, Fujimoto A, Tanaka Y, Shinohara M, Nagatsuma T, Shiokawa K, Obana Y, Miyoshi Y, Mita M, Takashima T, Shinohara I

Earth, Planets and Space Vol. 70 ( 1 ) 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER HEIDELBERG

© 2018, The Author(s). The fluxgate magnetometer for the Arase (ERG) spacecraft mission was built to investigate particle acceleration processes in the inner magnetosphere. Precise measurements of the field intensity and direction are essential in studying the motion of particles, the properties of waves interacting with the particles, and magnetic field variations induced by electric currents. By observing temporal field variations, we will more deeply understand magnetohydrodynamic and electromagnetic ion-cyclotron waves in the ultra-low-frequency range, which can cause production and loss of relativistic electrons and ring-current particles. The hardware and software designs of the Magnetic Field Experiment (MGF) were optimized to meet the requirements for studying these phenomena. The MGF makes measurements at a sampling rate of 256 vectors/s, and the data are averaged onboard to fit the telemetry budget. The magnetometer switches the dynamic range between ± 8000 and ± 60,000 nT, depending on the local magnetic field intensity. The experiment is calibrated by preflight tests and through analysis of in-orbit data. MGF data are edited into files with a common data file form

DOI： 10.1186/s40623-018-0800-1

Comparison of gravity wave propagation directions observed by mesospheric airglow imaging at three different latitudes using the M-transform Reviewed Open Access

Septi Perwitasari, Takuji Nakamura, Masaru Kogure, Yoshihiro Tomikawa, Mitsumu K. Ejiri, Kazuo Shiokawa

ANNALES GEOPHYSICAE Vol. 36 ( 6 ) page： 1597 - 1605 2018.11

Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

We developed user-friendly software based on Matsuda et al.'s (2014) 3D-FFT method (Matsuda-transform, M-transform) for airglow imaging data analysis as a function of Interactive Data Language (IDL). Users can customize the range of wave parameters to process when executing the program. The input for this function is a 3-D array of a time series of a 2-D airglow image in geographical coordinates. We applied this new function to mesospheric airglow imaging data with slightly different observation parameters obtained for the period of April-May at three different latitudes: Syowa Station, the Antarctic (69 degrees S, 40 degrees E); Shigaraki, Japan (35 degrees N, 136 degrees E); and Tomohon, Indonesia (1 degrees N, 122 degrees E). The day-to-day variation of the phase velocity spectrum at the Syowa Station is smaller and the propagation direction is mainly westward. In Shigaraki, the day-to-day variation of the horizontal propagation direction is larger than that at the Syowa Station; the variation in Tomohon is even larger. In Tomohon, the variation of the nightly power spectrum magnitude is remarkable, which indicates the intermittency of atmospheric gravity waves (AGWs). The average nightly spectrum obtained from April-May shows that the dominant propagation is westward with a phase speed < 50 m s(-1) at the Syowa Station and east-southeastward with a phase speed of up to similar to 80 m s(-1) in Shigaraki. The day-to-day variation in Tomohon is too strong to discuss average characteristics; however, a phase speed of up to similar to 100 m s(-1) and faster is observed. The corresponding background wind profiles derived from MERRA-2 indicate that wind filtering plays a significant role in filtering out waves that propagate eastward at the Syowa Station. On the other hand, the background wind is not strong enough to filter out relatively high-speed AGWs in Shigaraki and Tomohon and the dominant propagation direction is likely related to the distribution and characteristics of the source region, at least in April and May.

DOI： 10.5194/angeo-36-1597-2018

Microscopic Observations of Pulsating Aurora Associated With Chorus Element Structures: Coordinated Arase Satellite-PWING Observations Reviewed Open Access

Ozaki M, Shiokawa K, Miyoshi Y, Hosokawa K, Oyama S, Yagitani S, Kasahara Y, Kasaba Y, Matsuda S, Kataoka R, Ebihara Y, Ogawa Y, Otsuka Y, Kurita S, Moore R. C, Tanaka Y. -M, Nose M, Nagatsuma T, Connors M, Nishitani N, Katoh Y, Hikishima M, Kumamoto A, Tsuchiya F, Kadokura A, Nishiyama T, Inoue T, Imamura K, Matsuoka A, Shinohara I

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 22 ) page： 12125 - 12134 2018.11

Language：English Publishing type：Research paper (scientific journal)

Rapid (<1 s) intensity modulation of pulsating auroras is caused by successive chorus elements as a response to wave-particle interactions in the magnetosphere. Here we found that a pulsating auroral patch responds to the time spacing for successive chorus elements and possibly to chorus subpacket structures with a time scale of tens of milliseconds. These responses were identified from coordinated Arase satellite and ground (Gakona, Alaska) observations with a high-speed auroral imager (100 Hz). The temporal variations of auroral intensity in a few-hertz frequency range exhibited a spatial concentration at the lower-latitude edge of the auroral patch. The spatial evolution of the auroral patch showed repeated expansion/contraction with tens of kilometer scales in the ionosphere, which could be spatial behaviors in the wave-particle interactions. These observations indicate that chorus elements evolve coherently within the auroral patch, which is approximately 900 km in the radial and longitudinal directions at the magnetic equator.

DOI： 10.1029/2018GL079812

Statistical Analysis of SAR Arc Detachment From the Main Oval Based on 11-Year, AII-sky Imaging Observation at Athabasca, Canada Reviewed Open Access

Yuki Takagi, Kazuo Shiokawa, Yuichi Otsuka, Martin Connors, Ian Schofield

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 21 ) page： 11539 - 11546 2018.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report the first statistical analysis of stable auroral red (SAR) arc detachments from the main auroral oval, using 630-nm all-sky cooled-Charge Coupled Device images obtained at Athabasca (magnetic latitude = 61.7 degrees N), Canada. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of ring current particle injection in the inner magnetosphere. We analyzed all-sky images obtained for 11 years from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur in the premidnight sector, indicating the ring current ion drift to the dusk sector. The SAR arc detachments also tend to occur at the beginning of the substorm recovery phase, suggesting that the SAR arcs detach from the main oval as the main auroral oval returns to higher latitudes. The equatorward velocities of detached SAR arcs are from -100 m/s (poleward) to +200 m/s (equatorward), corresponding to magnetospheric electric fields from -1 to +2 mV/m.Plain Language, Summary Stable auroral red (SAR) arcs are the optical emissions caused by low-energy electron precipitation into the ionosphere from the inner magnetosphere close to the earth. In this paper, we report the first statistical analysis of SAR arc detachments from the main auroral oval, using all-sky cooled-Charge Coupled Device images measured at a wavelength of 630.0 nm obtained at Athabasca, Canada, which is located at latitudes just lower than the auroral zone latitudes. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of high-energy particle injection in the inner magnetosphere. We analyzed 11-year all-sky images from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur premidnight, indicating the high-energy ion drift to the dusk sector. We also found that the SAR arc detachments tend to occur at the beginning of the substorm recovery phase. This likely indicates that the SAR arcs detach from the high-latitude aurora as the main aurora returns to higher latitudes at the beginning of the recovery phase. The equatorward velocities of detached SAR arcs are also estimated from the analysis.

DOI： 10.1029/2018GL079615