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


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.


  1. Allan, W., E. M. Poulter, and S. P. White, Hydromagnetic wave coupling in the magnetosphere—plasmapause effects on impulse-excited resonances, Planet. Space Sci., 34, 1189–1200, 1986.

  2. Carpenter, D. L., Whistler studies of the plasmapause in the magnetosphere, 1, Temporal variations in the position of the knee and some evidence on the plasma motions on near knee, J. Geophys. Res., 71, 693–709, 1966.

  3. Chen, L. and A. Hasegawa, A theory of long-period magnetic pulsations, 2. Impulse excitation of surface eigen-mode, J. Geophys. Res., 79, 1033, 1974b.

  4. Cheng, C.-C, J.-K. Chao, and K. Yumoto, Spectral power of low-latitude Pi2 pulsations at the 210° magnetic meridian stations and plasmaspheric cavity resonances, Earth Planets Space, 52, 615–627, 2000.

  5. Dento, R. E., D.H. Lee, K. Takahashi, J. Goldstein, and R. Anderson, Quantitative test of the cavity resonance explanation of plasmaspheric PI2 frequencies, J. Geophys. Res., 107(A7), 10.1029/2001JA000272, 2002.

  6. Fujita, S. and M. Itonaga, A plasmaspheric virtual resonance in a longitudinally non-uniform plasmasphere, Earth Planets Space, 55, 219–222, 2003.

  7. Fujita, S., H. Nakata, M. Itonaga, A. Yoshikawa, and T. Mizuta, A numerical simulation of the Pi2 pulsations associated with the substorm current wedge, J. Geophys. Res., 107, 10.1029/2001JA900137, 2002.

  8. Gallagher, D. L., P. D. Craven, and R. H. Comfort, Global core plasma model, J. Geophys. Res., 105, 10819–10833, 2000.

  9. Keiling, A., J. R. Wygant, C. Cattel, K.-H. Kim, C. T. Russell, D. K. Milling, M. Temerin, F. S. Mozer, and C. A. Kletzing, Pi2 pulsations observed with the Polar satellite and ground stations: Coupling of trapped and propagating fast mode waves to a midlatitude field line resonance, J. Geophys. Res, 106, 25891–25904, 2001.

  10. Kosaka, K., T. Iyemori, M. Nosé, M. Bitterly, and J. Bitterly, Local time dependence of the dominant frequency of Pi2 pulsations at mid- and low-latitudes. Earth Planets Space, 54, 771–781, 2002.

  11. Lanzerotti, L. J. and L. Medford, Local night, impulsive (Pi2 type) dydro-magnetic wave polarization at low latitudes, Planet. Space Sci., 32, 135, 1984.

  12. Lee, D.H., Dynamics of MHD wave propagation in the low-latitude magnetosphere, J. Geophys. Res., 101, 15371–15386, 1996.

  13. Lee, D.H. and R. Lysak, MHD waves in a three-dimensional dipolar magnetic field: a search for Pi2 pulsations, J. Geophys. Res., 104, 28691–28699, 1999.

  14. Lester, M. and D. Orr, Correlations between ground observations of Pi2 geomagnetic pulsations and satellite plasma density observations, Planet. Space Sci., 31, 143, 1989.

  15. Lester, M., W. J. Hughes, and H. J. Singer, Polarization patterns of Pi2 magnetic pulsations and the substorm current wedge, J. Geophys. Res., 88, 7958–7966, 1983.

  16. Lester, M., W. J. Hughes, and H. J. Singer, Longitudinal structure in Pi2 pulsation and the substorm current wedge, J. Geophys. Res., 89, 5489–5494, 1984.

  17. Nosé, M., T. Iyemori, M. Takeda, T. Kamei, D. K. Milling, D. Orr, H. J. Singer, E. W. Worthington, and N. Sumitomo, Automated detection of Pi2 pulsations using wavelet analysis: 1. Method and an application for substorm monitoring, Earth Planets Space, 50, 773–783, 1998.

  18. Nosé, M., K. Takahashi, T. Uozumi, K. Yumoto, Y. Miyoshi, A. Morioka, D. K. Milling, P. R. Sutcliffe, H. Matsumoto, T. Goka, and H. Nakata, Multipoint observations of a Pi2 pulsation on morning side: The 20 September 1995 event, J. Geophys. Res., 108(A5), 1219, doi: 10.1029/2002Ja009747, 2003.

  19. Olson, J. V., Pi2 pulsations and substorm onsets: A review, J. Geophys. Res., 104, 17499–17520, 1999.

  20. Sutcliffe, P. R., The association of harmonics in Pi2 power spectra with the plasmapause, Planet. Space Sci., 23, 1581–1587, 1975.

  21. Sutcliffe, P. R. and K. Yumoto, Dayside Pi2 pulsations at low latitudes, Geophys. Res. Lett., 16, 887–890, 1989.

  22. Sutcliffe, P. R. and K. Yumoto, On the cavity mode nature of low latitude Pi2 pulsations, J. Geophys. Res., 96, 1543–1551, 1991.

  23. Takahashi, K., S.-i. Ohtani, and B. J. Anderson, Statistical analysis of Pi 2 pulsations observed by the AMPTE CCE spacecraft in the inner magnetosphere, J. Geophys. Res., 100, 21929–21941, 1995.

  24. Takahashi, K., D.H. Lee, M. Nose, R. R. Anderson, W. J. Hughes, CRRES electric field study of the radial mode structure of Pi2 pulsations, J. Geophys. Res., 108(A5), 1210, doi:10.1029/2002JA009761, 2003.

  25. Ulrych, T. J. and T. N. Bishop, Maximum entropy spectral analysis and autoregressive decomposition, Reviews of Geophysics and Space Physics, 13, 183–200, 1975.

  26. Yeoman, T. K. and D. Orr, Phase and spectral power of mid-latitude Pi2 pulsations: Evidence for a plasmaspheric cavity resonance, Planet. Space Sci, 37, 1367–1383, 1989.

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Correspondence to Desheng Han.

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Han, D., Iyemori, T., Gao, Y. et al. Local time dependence of the frequency of Pi2 waves simultaneously observed at 5 low-latitude stations. Earth Planet Sp 55, 601–612 (2003).

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Key words

  • Pi2
  • frequency
  • LT dependence
  • low-latitude
  • simultaneous observation