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タイトル: Magnetic ripples observed by Swarm satellites and their enhancement during typhoon activity
著者: Aoyama, Tadashi
Iyemori, Toshihiko
Nakanishi, Kunihito
著者名の別形: 青山, 忠司
家森, 俊彦
中西, 邦仁
キーワード: Magnetic ripple
Magnetic fluctuation
Field-aligned current
Ionospheric dynamo
Acoustic wave
Gravity wave
Typhoon
Tropical cyclone
Swarm satellites
Cumulus convection
発行日: 3-Jul-2017
出版者: Springer Nature
誌名: Earth, Planets and Space
巻: 69
論文番号: 89
抄録: The Swarm satellites observed small-amplitude (0.1–5 nT) magnetic fluctuations perpendicular to the geomagnetic field. These so-called magnetic ripples (MRs) have a period of around a few tens of seconds along the satellite orbit in the topside ionosphere at middle and low latitudes. They are spatial structures from small-scale field-aligned currents. We investigated the following three characteristics of the MRs. First, we used Swarm observations to confirm their basic characteristics obtained from the Challenging Minisatellite Payload satellite. That is, the global distribution of the average MR amplitudes has clear geographic, seasonal, and local time dependence that is highly correlated with ionospheric conductivities. Second, we found that the average amplitudes of the MRs derived from the Swarm-B satellite, which flies at a ~50 km higher altitude, are slightly smaller than those of the Swarm-A and Swarm-C. This difference suggests that the location of the origin of MRs is below ~460 km altitude, i.e., not in the magnetosphere. Last, to provide evidence of correlation between the MRs and meteorological phenomena, we performed statistical and event analyses with typhoon track data, which are a source of acoustic and gravity waves. The data from 54 typhoons during the period from November 26, 2013, to July 31, 2016, were used for statistical analysis. The results show that the average amplitudes of the MRs during typhoon activity on the dawn, dusk, and night sides are larger than those during non-typhoon conditions. Event analyses indicate amplitude enhancements of the MRs around typhoons, and the latitude of the enhancement migrated with the typhoon. These analyses indicate that typhoon activity is correlated with MR activity and that cumulus convection activity other than typhoons may also affect MR amplitudes.
著作権等: © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
URI: http://hdl.handle.net/2433/227885
DOI(出版社版): 10.1186/s40623-017-0679-2
出現コレクション:学術雑誌掲載論文等

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