Local time dependence of the frequency of Pi2 waves simultaneously observed at 5 low-latitude stations

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  • Han Desheng
    Department of Geophysics, Graduate School of Science, Kyoto University
  • Iyemori Toshihiko
    Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University
  • Gao Yufen
    Institute of Geophysics, CSB
  • Sano Yasuharu
    Department of Information Management, School of Business Administration, Asahi University
  • Yang Fuxi
    Urumqi Basic Seismic Station Urumqi
  • Li Wansheng
    Yinchuan Geomagnetic Observatory
  • Nosé Masahito
    Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University

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Description

One-second resolution geomagnetic data from 5 stations located at low-latitudes (i.e., L = 1.2-1.6) were used to examine the local time dependence of the dominant frequency of Pi2 pulsations. We analyzed 183 Pi2 events simultaneously recorded at the 5 stations and discussed their possible generation mechanisms. The averaged dominant frequency of the H (horizontal) component is higher on the dawn side than that on the dusk side and shows a peak value in the post-midnight at around 03 LT, which confirms the LT dependence previously suggested from single station data (i.e., non-simultaneous observation). However, some of the events have no LT dependence. For the events which show the LT dependence at low-latitudes, we infer that the cavity resonance mode is a plausible generation mechanism, but we do not rule out the possibility of the plasmaspheric surface wave mode which has also been suggested. For the events having a common frequency between the eastern and western stations, we suggest the cavity resonance mode to be the mechanism. The averaged dominant frequency of the D component does not show any clear LT dependence, and only about 20% of Pi2s have identical frequency for both the H and D components, therefore we suggest that the H and D oscillations of Pi2s are generated from different mechanisms. We also found that the frequency of different parts of a Pi2 pulsation, i.e., the dominant frequency for leading part and trailing part of the pulsation, is different, and the frequency of the trailing part is lower than that of the leading part.

Journal

  • Earth, Planets and Space

    Earth, Planets and Space 55 (10), 601-612, 2003

    Society of Geomagnetism and Earth, Planetary and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan , The Geodetic Society of Japan , The Japanese Society for Planetary Sciences

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