SC-triggered plasma waves observed by the Akebono satellite in the polar regions and the plasmasphere

Plasma wave phenomena associated with sudden commencements (SCs) were analyzed based on observations conducted with the Akebono satellite, which has been collecting data for more than 13 years (since March 1989). Simultaneous plasma wave observation data for 257 SCs reveal that enhanced plasma waves are observed with an exact one-to-one correspondence with the SCs throughout the entire observation region, including the polar and plasmasphere regions. Electromagnetic whistler mode and ion cyclotron waves are enhanced in the low latitude plasmasphere, while electrostatic whistler mode and electromagnetic ion cyclotron waves are generated in the polar region. The onset times of the SC-triggered plasma waves exhibit a delay or lead time characteristic, compared with the onset times of SCs identified by the Kakioka Magnetic Observatory, with a time resolution of 1 s. By comparing the difference in SCs and enhanced electron plasma waves onset times, the propagation route of the SC disturbances can be identified in the plasmasphere

Inner belt and slot region electron lifetimes and energization rates based on AKEBONO statistics of whistler waves

International audienceGlobal statistics of the amplitude distributions of hiss, lightning-generated, and other whistlermode waves fromterrestrial VLF transmitters have been obtained from the EXOS-D (Akebono) satellite in theEarth’s plasmasphere and fitted as functions of L and latitude for two geomagnetic activity ranges (Kp 3). In particular, the present study focuses on the inner zone L ∈ [1.4, 2] where reliable in situmeasurements were lacking. Such statistics are critically needed for an accurate assessment of the role andrelative dominance of each type of wave in the dynamics of the inner radiation belt. While VLF waves seemto propagate mainly in a ducted mode at L ∼ 1.5–3 for Kp 3). Hiss waves are generally the most intense in the inner belt, andlightning-generated and hiss wave intensities increase with geomagnetic activity. Lightning-generatedwave amplitudes generally peak within 10◦ of the equator in the region L < 2 where magnetosonic waveamplitudes are weak for Kp < 3. Based on this statistics, simplified models of each wave type are presented.Quasi-linear pitch angle and energy diffusion rates of electrons by the full wave model are then calculated.Corresponding electron lifetimes compare well with decay rates of trapped energetic electrons obtainedfrom Solar Anomalous and Magnetospheric Particle Explorer and other satellites at L ∈ [1.4, 2]

Statistical study on propagation characteristics of Omega signals (VLF) in magnetosphere detected by the Akebono satellite

This paper shows a statistical analysis of 10.2 kHz Omega broadcasts of an artificial signal broadcast from ground stations, propagated in the plasmasphere, and detected using an automatic detection method we developed. We study the propagation patterns of the Omega signals to understand the propagation characteristics that are strongly affected by plasmaspheric electron density and the ambient magnetic field. We show the unique propagation patterns of the Omega 10.2 kHz signal when it was broadcast from two high-middle-latitude stations. We use about eight years of data captured by the Poynting flux analyzer subsystem on board the Akebono satellite from October 1989 to September 1997. We demonstrate that the signals broadcast from almost the same latitude (in geomagnetic coordinates) propagated differently depending on the geographic latitude. We also study propagation characteristics as a function of local time, season, and solar activity. The Omega signal tended to propagate farther on the nightside than on the dayside and was more widely distributed during winter than during summer. When solar activity was at maximum, the Omega signal propagated at a lower intensity level. In contrast, when solar activity was at minimum, the Omega signal propagated at a higher intensity and farther from the transmitter station.Comment: 14 pages, 12 figure

Similar Data Retrieval from Enormous Datasets on ELF/VLF Wave Spectrum Observed by Akebono

金沢大学総合メディア基盤センターAs the total amount of data measured by scientific spacecraft is drastically increasing, it is necessary for researchers to develop new computation methods for efficient analysis of these enormous datasets. In the present study, we propose a new algorithm for similar data retrieval. We first discuss key descriptors that represent characteristics of the VLF/ELF waves observed by the Akebono spacecraft. Second, an algorithm for similar data retrieval is introduced. Finally, we demonstrate that the developed algorithm works well for the retrieval of the VLF spectrum with a small amount of CPU load

Simultaneous ground-based and satellite observations of natural VLF waves in Antarctica: A case study of downward ionospheric penetration of whistler-mode waves

AbstractTo investigate downward ionospheric-penetration characteristics of VLF (several hundred Hz to 17.8 kHz) whistler-mode waves, we conducted simultaneous observations (in 2006) of natural VLF waves using both ground stations in Antarctica and the Japanese Akebono satellite. The ground-based and satellite observations included an interesting event for which both observed similar VLF waves. In this study, we theoretically calculate down-going whistler-mode wave propagation based on ground-satellite observations using the full-wave analysis. In a case study, the observed wave-normal angles were approximately 140–160 degrees for a dayside chorus event on 15 March 2006. The theoretical calculation showed that the wave-normal angles for ionospheric penetration should be around 155.6 degrees, with its angular width of approximately 2 degrees. Moreover, the wave-energy loss due to ionospheric penetration is estimated at 20.4 dB based on our theoretical calculation, in accordance with the observed 17–19 dB

Study on Omega Signals Observed by Poynting Flux Analyzer on board the Akebono Satellite

13301甲第4546号博士（工学）金沢大学博士論文要旨Abstract 以下に掲載：International Journal of Advanced Computer Science and Applications 7(10) pp.67-74 2016. The Science and Information (SAI) Organization Limited. 共著者：I Made Agus Dwi Suarjaya, Yoshiya Kasahara, Yoshitaka Got

Relationship between low-frequency electric-field fluctuations and ion conics around the cusp/cleft region

We investigated the relationship between low-frequency (0.2-4.0 Hz) electric-field fluctuations (LEFs) and ion conics around the dayside cusp/cleft region in the altitude range from 5000 to 10000km from observations made by the Akebono satellite. Ion conics were generally associated with intense LEFs. We found a significant correlation between the power spectral density of LEFs at any frequency and the energy of simultaneously observed ion conics. Ion conics with a conic angle near 90 deg and those more aligned with magnetic field lines both had an equivalent correlation with the local intensity of the LEFs. The LEFs associated with near-perpendicular ion conics were, however, generally more intense than those associated with folded conics. The difference was clearer for low-energy conics. These results are in agreement with a scenario of height-integrated heating of ions and energization of ions by electromagnetic energy supplied by local LEFs. Ions generally stay in the energization region during their upward motion along the field line, so that more folded ion conics with weak energization reach the same energy level as near-perpendicular conics with strong energization, due to the difference in integration time. The limit on residence time in the intense heating region causes the clearer difference for low-energy conics. We set up a simple model to examine the relationship between the energization rate and the evolution of ion conics along the field lines, and obtained good agreement with the observation results

Diagnostics of Multicomponent Plasma Using EMIC Waves Observed by the Akebono Satellite

13301甲第4238号博士（工学）金沢大学博士論文本文Full 以下に掲載：1.電子情報通信学会論文誌B J95-B(11) pp.1584-1593 2012. 一般社団法人 電子情報通信学会. 共著者：松田, 昇也, 笠原, 禎也, 後藤, 由貴 2.Geophysical Research Letters 41(11) pp.3759-3765 2014. American Geophysical Union. 共著者：Shoya Matsuda, Yoshiya Kasahara, Yoshitaka Goto 3.Journal of Geopysical Research 119(6) pp.4348-4357 2014. American Geophysical Union. 共著者：Shoya Matsuda, Yoshiya Kasahara, Yoshitaka Goto 4.Journal of Geopysical Research 120(4) 2015. American Geophysical Union. 共著者：Shoya Matsuda, Yoshiya Kasahara, Yoshitaka Goto　 　

Radio emissions of auroral origin observable at ground level: outstanding problems

Auroral radio emissions are of intrinsic interest as part of the Earth’s environment but also provide remote sensing of ionospheric conditions and processes and a laboratory for emission processes applicable to a wide range of space and astrophysical plasmas. At VLF and above, four broad classes of radio emissions occur. All have been observed with ground-based and, in some cases to a lesser degree, with space-based instruments. Related to each type of radio emission, many experimental and theoretical challenges remain, for example: explanations of frequency and time structure, relations to auroral substorms or current systems, and application to remote sensing of the auroral ionosphere. In some cases, basic parameters such as source heights or generation mechanisms are uncertain. Emerging technological advances such as cubesat fleets, ultra-large capacity disk drives, and software defined radio show promise for developing better understanding of auroral radio emissions