Wp index: A new substorm index derived from high-resolution geomagnetic field data at low latitude

Publication: Research - peer-reviewJournal article – Annual report year: 2012



  • Author: Nose, M.

    Kyoto University, Japan

  • Author: Iyemori, T.

    Kyoto University, Japan

  • Author: Wang, L.

    Geoscience Australia, Australia

  • Author: Hitchman, A.

    Geoscience Australia, Australia

  • Author: Matzka, Jürgen

    Solar System Physics, National Space Institute, Technical University of Denmark, Elektrovej, 2800, Kgs. Lyngby, Denmark

  • Author: Feller, M.

    Ludwig-Maximilians-Universität, Germany

  • Author: Egdorf, S.

    Ludwig-Maximilians-Universität, Germany

  • Author: Gilder, S.

    Ludwig-Maximilians-Universität, Germany

  • Author: Kumasaka, N.

    Japan Meteorological Agency, Japan

  • Author: Koga, K.

    Japan Aerospace Exploration Agency, Japan

  • Author: Matsumoto, H.

    Japan Aerospace Exploration Agency, Japan

  • Author: Koshiishi, H.

    Japan Aerospace Exploration Agency, Japan

  • Author: Cifuentes-Nava, G.

    Universidad Nacional Autonoma de Mexico, Mexico

  • Author: Curto, J. J.

    Universitat Ramon Llull, Spain

  • Author: Segarra, A.

    Universitat Ramon Llull, Spain

  • Author: Celik, C.

    Boğazici University, Turkey

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Geomagnetic field data with high time resolution (typically 1 s) have recently become more commonly acquired by ground stations. Such high time resolution data enable identifying Pi2 pulsations which have periods of 40-150 s and irregular (damped) waveforms. It is well-known that pulsations of this type are clearly observed at mid-and low-latitude ground stations on the nightside at substorm onset. Therefore, with 1-s data from multiple stations distributed in longitude around the Earth's circumference, substorm onset can be regularly monitored. In the present study we propose a new substorm index, the Wp index (Wave and planetary), which reflects Pi2 wave power at low-latitude, using geomagnetic field data from 11 ground stations. We compare the Wp index with the AE and ASY indices as well as the electron flux and magnetic field data at geosynchronous altitudes for 11 March 2010. We find that significant enhancements of the Wp index mostly coincide with those of the other data. Thus the Wp index can be considered a good indicator of substorm onset. The Wp index, other geomagnetic indices, and geosynchronous satellite data are plotted in a stack for quick and easy search of substorm onset. The stack plots and digital data of the Wp index are available at the Web site (http://s-cubed.info) for public use. These products would be useful to investigate and understand space weather events, because substorms cause injection of intense fluxes of energetic electrons into the inner magnetosphere and potentially have deleterious impacts on satellites by inducing surface charging. Citation: Nose, M., et al. (2012), Wp index: A new substorm index derived from high-resolution geomagnetic field data at low latitude, Space Weather, 10, S08002, doi:10.1029/2012SW000785.
Original languageEnglish
JournalSpace Weather
Pages (from-to)-
StatePublished - 2012
CitationsWeb of Science® Times Cited: 21
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