Skip to main content

Daily variations of geomagnetic HD and Z-field at equatorial latitudes


With the establishment of the new geomagnetic field observations in the Ocean Hemisphere Network Project (OHP) in Japan, minutes values of geomagnetic components, H D and Z have been recorded. The hourly mean values were used to study the variations in these three components at these new equatorial electrojet regions. The results of the analysis carried out revealed that the amplitude of d H has diurnal variation which peaks during the day at about local noon in all the three equatorial electrojet regions. This diurnal variation in H with Sq (H) enhancement in all the three regions are attributed to the enhanced dynamo action at these regions. Diurnal variation as observed in D indicates that the equatorial electrojet current system has both east-west and north-south components. The pronounced magnitude of Z variation as observed in Kiritimati is attributed mainly to sea induction. Also some abnormal features were observed on 23rd of January at Huancayo, in the components. Seasonal variations with more pronounced equinoctial maximum were observed in H than in Z. D component showed no consistent seasonal variation in all the regions. The equinoctial maximum is due to enhanced equatorial electron density at equinox. More research work, if carried out in these new regions will be useful in making more new contributions to the field of the dynamics of the equatorial electrojet region.


  • Alex, S., B. D. Kadam, and R. G. Rastogi, A new aspect of daily variations of the geomagnetic field at low latitude, J. Atmos. Terr. Phys., 54(7/8), 863–869, 1992.

    Article  Google Scholar 

  • Bartels, J. and H. F. Johnston, Geomagnetic tides in horizontal intensity at Huancayo-part1, J. Geophys. Res., 45, 264–308, 1940.

    Google Scholar 

  • Chapman, S., The solar and lunar variation of the earth’s magnetism, Phil. Trans. R. Soc. Lond., A 218, 1–118, 1919.

    Article  Google Scholar 

  • Chapman, S., The equatorial electrojet as detected from the abnormal electric current distribution above Huancayo, Peru, and elsewhere, Arch. Meteorol. Geophys. Bioclimatol. A, 4, 368–390, 1951.

    Article  Google Scholar 

  • Chapman, S. and K. O. Rajarao, The H and Z variation along and near equatorial electrojet in India, Africa and the Pacific, J. Atmos. Terr. Phys., 27, 559–581, 1965.

    Article  Google Scholar 

  • Doumouya, V., J. Vassal, Y. Cohen, O. Fambitakoye, and M. Menvielle, Equatorial electrojet at African longitudes: First results from magnetic measurements, Ann. Geophys., 16, 658–676, 1998.

    Article  Google Scholar 

  • Egedal, J., The magnetic diurnal variation of the horizontal force near the magnetic equator, Terr. Magn. Atmos. Electr, 52, 449–451, 1947.

    Article  Google Scholar 

  • Fambitakoye, O., Variabilité jour-à-jour de la variation journalière régulière du champ magnétique terrestre dans la région de l’électrojet équatorial. C. R. AcadSci. Paris, 272, 637–640, 1971.

    Google Scholar 

  • Fambitakoye, O. and P. N. Mayaud, Equatorial electrojet and regular daily variation SR-1: A determination of the equatorial electrojet parameters, J. Atmos. Terr. Phys., 38, 1–17, 1976a.

    Article  Google Scholar 

  • Fambitakoye, O. and P. N. Mayaud, Equatorial electrojet and daily variation SR-2: The centre of the equatorial electrojet, J. Atmos. Terr. Phys., 38, 19–26, 1976b.

    Article  Google Scholar 

  • Forbush, S. E. and M. Casaverde, The equatorial electrojet in Peru, Carnegie Inst. Washington Publication, 620, 135 pp., 1961.

  • Maeda, H., T. Iyemori, T. Araki, and T. Kamei, New evidence of ameridional current system in the equatorial ionosphere, Geophys. Res. Lett, 9, 337–340, 1982.

    Article  Google Scholar 

  • Okeke, F. N., C. A. Onwumechili, and B. A. Rabiu, Day-to-day variability of geomagnetic hourly amplitudes at low latitudes, Geophys. J. Int., 134, 484–500, 1998.

    Article  Google Scholar 

  • Onwumechili, C. A., Spatial and temporal distributions of ionospheric currents in subsolar elevations, J. Atmos. Terr. Phys., 59, 1891–1899, 1997.

    Article  Google Scholar 

  • Patil, A., B. R. Arora, and R. G. Rastogi, Daily variations of the geomagnetic field near the focus in Sq current system of Indian longitude, Proc. Indian Acad. Sci., 92, 239–245, 1983.

    Google Scholar 

  • Patil, A. R., D. R. K. Rao, and R. G. Rastogi, Equatorial Electrojet strengths in the Indian and American Sectors: Part 1. During low solar activity, J. Geomag. Geoelectr, 42, 801–811, 1990.

    Article  Google Scholar 

  • Rastogi, R. G., Westward equatorial electrojet during daytime hours, J. Geophys. Res., 79, 1503–1512, 1974.

    Article  Google Scholar 

  • Rastogi, R. G., Solar flare effects on zonal and meridional current at the equatorial electrojet station, Annamalainagar, J. Atmos Terr. Phys., 58(13) 1413–1420, 1996.

    Article  Google Scholar 

  • Shimizu, H. and H. Utada, Ocean Hemisphere Geomagnetic Network: its instrumental design and perspective for long-term geomagnetic observations in the pacific, Earth Planets Space, 51, 917–932, 1999.

    Article  Google Scholar 

  • Tarpley, J. D., Seasonal movement of the Sq current foci and related effects in the equatorial electrojet, J. Atmos. Terr. Phys., 35, 1063–1071, 1973.

    Article  Google Scholar 

Download references

Author information

Authors and Affiliations


Corresponding author

Correspondence to F. N. Okeke.

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Okeke, F.N., Hamano, Y. Daily variations of geomagnetic HD and Z-field at equatorial latitudes. Earth Planet Sp 52, 237–243 (2000).

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


  • Diurnal Variation
  • Daily Variation
  • Equatorial Electrojet
  • Dynamo Action
  • Equatorial Latitude