Skip to main content

Frequency dependence of equatorial electrojet effect on geomagnetic micropulsations


The micropulsation data (Pc3–Pc4 range) from off-equatorial and equatorial stations Alibag (ABG) and Tirunelvelli (TIR) in the Indian zone during 1991 are analysed for delineating the electrojet effect. The ratios of the spectral amplitudes at significant frequency bands the horizontal component of the magnetic field at TIR to that at ABG are worked out as a function of frequency. The results show that the lower frequencies undergo larger equatorial amplification. However, above a certain frequency the pulsation signal is found to attenuate rather than exhibit the general enhancement. The ratio becomes minimum around the period, 18 to 24 sec. At further higher frequencies, there is again the normal electrojet amplification. The explanation of such a behaviour of the electrojet on the pulsation amplitude is rather difficult at the present stage and to some extent becomes controversial even if it is offered.


  • Green, A. W. and E. W. Worthington, Alfven field line resonance at low latitude (L = 1.5), J. Geophys. Res., 98, 15693–15699, 1993.

    Article  Google Scholar 

  • Hattingh, S. K. F. and P. R. Sutcliffe, Pc 3 pulsation Eigenperiods determination at low latitudes, J. Geophys. Res., 92, 12433–12436, 1987.

    Article  Google Scholar 

  • Hughes, W. J. and D. J. Southwood, The screening of micropulsation signals by the atmosphere and the ionosphere, J. Geophys. Res., 81, 3234–3240, 1976.

    Article  Google Scholar 

  • Matsuoka, H., K. Takahashi, S. Kokubun, K. Yumoto, T. Yamamoto, S. I. Solovyev, and E. F. Vershinin, Phase and amplitude structure of Pc 3 magnetic pulsations as determined from multipoint observations, J. Geophys. Res., 102, 2391–2403, 1997.

    Article  Google Scholar 

  • Newton, R. S., D. J. Southwood, and W. J. Hughes, Damping of geomagnetic pulsation by the ionosphere, Planet. Space Sci., 26, 201–209, 1978.

    Article  Google Scholar 

  • Orr, D. and J. A. D. Mathew, The variation of geomagnetic micropulsation periods with latitude, Planet. Space Sci., 19, 897–905, 1971.

    Article  Google Scholar 

  • Osaki, H., K. Yumoto, K. Fukao, K. Shiokawa, F. W. Menk, B. J. Fraser, and the 210° MM Magnetic Observation Group, Characteristics of low-latitude Pi 2 pulsations along the 210° Magnetic Meridian, J. Geomag. Geoelectr., 48, 1421–1430, 1996.

    Article  Google Scholar 

  • Poulter, E. M., W. Allan, G. J. Bailey, and R. J. Moffett, On the diurnal period variation of midlatitude ULF pulsations, Planet. Space Sci., 32, 727–734, 1984.

    Article  Google Scholar 

  • Poulter, E. M., W. Allan, and G. J. Bailey, ULF pulsation eigen periods within the plasmasphere, Planet. Space Sci., 36, 185–196, 1988.

    Article  Google Scholar 

  • Saito, T., K. Yumoto, M. Seto, S. I. Akasofu, E. J. Smith, and B. T. Tsurutani, Characteristics of Pc 3’s recorded simultaneously by rulfmeters at Circem Northern Pacific station, Proc. 4th IAGA Scientific Assembly, Edinburgh, 1981.

  • Sarma, S. V. S. and T. S. Sastry, On the equatorial electrojet influence on geomagnetic pulsation amplitude, J. Atmos. Terr. Phys., 57, 749–754, 1995.

    Article  Google Scholar 

  • Sastry, T. S., Y. S. Sarma, and S. V. S. Sarma, Equatorial electrojet effect on Geomagnetic pulsations, Ind. J. Rad. Space Phys., 8, 249–253, 1979.

    Google Scholar 

  • Shinohara, M., K. Yumoto, A. Yoshikawa, O. Saka, S. I. Solovyev, E. F. Vershinin, N. B. Trivedi, J. M. Da Costa, and The 210° MM Magnetic Observation Group, Wave characteristics of day time and night time Pi 2 pulsations at the equatorial and low latitudes, Geophys. Res. Lett., 24, 2279–2282, 1997.

    Article  Google Scholar 

  • Singer, H. J., D. J. Southwood, R. J. Walker, and M. G. Kivelson, Alfven wave resonances in a realistic magnetospheric magnetic field geometry, J. Geophys. Res., 86, 4589–4596, 1981.

    Article  Google Scholar 

  • Udare, R. S., Geomagnetic pulsations (Pc3-Pc4) recording system: hardware and software, Geol. Soc. India Mem., 24, 241–251, 1992.

    Google Scholar 

  • Vellante, M., U. Villante, M. De Lauretis, and P. Cerulli-Irelli, An analysis of micropulsation events at a low latitude station during 1985, Planet. Space Sci., 37, 767–773, 1989.

    Article  Google Scholar 

  • Yumoto, K., V. A. Pilipenko, E. N. Fedorov, N. A. Kurneva, and Yu. G. Habazin, Mechanism of damping of geomagnetic pulsations at low latitude, Geomagn. Aeron., 33, 593–598, 1994 (English Translation).

    Google Scholar 

  • Yumoto, K., V. A. Pilipenko, E. Fedorov, N. Kurneva, and K. Shiokawa, The mechanism of damping of geomagnetic pulsations, J. Geomag. Geoelectr., 47, 163–176, 1995a.

    Article  Google Scholar 

  • Yumoto, K. and The 210° MM Magnetic Observation Group, Initial results from the 210° magnetic meridian project-Review, J. Geomag. Geoelectr., 47, 1197–1213, 1995b.

    Article  Google Scholar 

Download references

Author information

Authors and Affiliations


Corresponding author

Correspondence to M. Roy.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Roy, M., Rao, D.R.K. Frequency dependence of equatorial electrojet effect on geomagnetic micropulsations. Earth Planet Sp 50, 847–851 (1998).

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


  • Pulsation Signal
  • Geomagnetic Pulsation
  • Indian Zone
  • Toroidal Mode
  • Hydromagnetic Wave