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Equatorial electrojet as a diagnostic tool of geomagnetic field models

Abstract

The equatorial electrojet (EEJ) is a unique feature of the Earth’s external current systems because it must flow along the dip equator. This provides us with a tool to determine the nature of the variations imposed by competing main field models on the equatorial region. First we show that for certain regions a comparison between scalar geomagnetic measurements that use different models to remove the main field may not be reasonable. Next we found the intrinsic error in the determination of the possible location of the dip equator was ±9.8 km (0.088°) at 108 km altitude for the models shown here. Using scalar measurements from over 14,000 CHAMP satellite passes, the latitude of the maximum of the EEJ field at the satellite altitude was determined by subtracting four different models of the main field. We find that the location can be statistically determined to within ±0.5° of the dip equator (calculated at 108 km altitude) irrespective of longitude, time of the measurement, degree of magnetic activity, and subtracted model. However, variations of the latitude of the maximum EEJ field with longitude are sometimes caused by the actual model and are not always a physical phenomenon. By choosing one model, and assuming it is the best representation of the main field, we have also shown that the accuracy of determination of the position of the EEJ signal is reduced in the morning and evening hours and that a morning and evening shift in the location of the EEJ found using ground measurements is also seen here. There exists a clear annual variation in the position of the EEJ regardless of longitude: it is south of the dip equator in December which is in agreement with the findings of all previous studies.

References

  • Butcher, E. C. and D. M. Schlapp, The annual variation of the night-time values of the geomagnetic field, Geophys. J. Int., 111, 151–158, 1992.

    Article  Google Scholar 

  • Chambodut, A., J. Schwarte, G. B. Langlais, H. Lühr, and M. Mandea, The selection of data in field modeling, Oist-4 Proceedings: 4th Ørsted International Science Team Conference, Copenhagen, September 23-27, 2002, edited by P. Stauning, H. Lühr, P. Ultre-Geurard, J. LaBrecque, M. Purucker, F. Primdahl, J. Joergenson, F. Christiansen, P. Hoeg, and K. Lauritsen, Narayana Press. pp. 31–34, 2003.

  • Chapman, S. and J. Bartels, Geomagnetism Vols. I and II, Oxford University Press, 1940.

    Google Scholar 

  • Deka, R. C, L. A. D’Cruz, V. J. Jacob, A. Iype, and P. Elango, Location of the dip equator over Peninsular India, J. Ind. Geophys. Union., 9(1), 41–46, 2005.

    Google Scholar 

  • Fambitakoye, O. and P. N. Mayaud, Equatorial Electrojet and Regular Daily Variation SR—I. A Determination of the Equatorial Electrojet Parameters, J. Atmos. Terr. Phys., 38, 1–17, 1976/1.

    Article  Google Scholar 

  • Fambitakoye, O. and P. N. Mayaud, Equatorial Electrojet and Regular Daily Variation SR—II. The Centre of the Equatorial Electrojet, J. Atmos. Terr. Phys., 38, 19–26, 1976/2.

    Article  Google Scholar 

  • Fambitakoye, O. and P. N. Mayaud, Equatorial Electrojet and Regular Daily Variation SR—IV Special Features in Particular Days, J. Atmos. Terr. Phys., 38, 123–134, 1976/3.

    Article  Google Scholar 

  • Fambitakoye, O., P. N. Mayaud, and A. D. Richmond, Equatorial Electrojet and Regular Daily Variation SR-III. Comparison of Observations with a Physical Model, J. Atmos. Terr. Phys., 38(2) 113–121, 1976.

    Article  Google Scholar 

  • Forbes, J. M., The equatorial electrojet, Rev. Geophys. Space Phys., 19, 469–504, 1981.

    Article  Google Scholar 

  • Holme, R., N. Olsen, M. Rother, and H. Lühr, C02—A CHAMP Magnetic Field Model, in First CHAMP Mission Results for Gravity, Magnetic and Atmospheric Studies, edited by C. Reigber, H. Lühr, and P. Schwintzer, Springer, Berlin; Praxis Publishing. pp. 220(6), 2003.

    Chapter  Google Scholar 

  • Jadhav, G., M. Rajaram, and R. Rajaram, Main Field Control of the Equatorial Electrojet: a Preliminary Study from the Oersted Data, J. Geodynamics, 33, 157–171, 2002.

    Article  Google Scholar 

  • Langel, R. A. and R. H. Estes, A geomagnetic field spectrum, Geophys. Res. Lett., 9, 250–253, 1982.

    Article  Google Scholar 

  • Lowes, F. J. and J. E. Martin, Optimum use of satellite intensity and vector data in modelling the main geomagnetic field, PEPI, 48, 3–4(10): 183–192, 1987.

    Google Scholar 

  • Lühr H., S. Maus, and M. Rother, Noon-time equatorial electrojet: Its spatial features as determined by the CHAMP satellite, J. Geophys. Res., 109, A01306, 2004, doi:10.1029/2002JA009656.

  • Malin, S. R. and A. M. Isikara, Annual variation of the geomagnetic field, Geophys. J. R. Astr. Soc, 47, 445–457, 1976.

    Article  Google Scholar 

  • Martinec, Z. and H. McCreadie, Magnetic induction modelling based on satellite magnetic vector data, Geophys. J. Int., 157, 1045–1060, 2004 doi: 10.1111/j.1365-246X.2004.02252.x.

    Article  Google Scholar 

  • Maus, S., M. Rother, R. Holme, H. Lühr, N. Olsen, and V. Haak, First scalar magnetic anomaly map from CHAMP satellite data indicates weak lithospheric field, Geophys. Res. Lett., 29, 2002, doi:10.1029/2001GL013685.

  • McCreadie H., Annual and Semi-annual harmonics of the midnight geomagnetic field, Ph.D thesis, Bochardt library, LaTrobe University, Bundoora Australia, 1998.

    Google Scholar 

  • McCreadie H., Classes of the equatorial electrojet, Earth Observation with CHAMP Results from Three Years in Orbit, Springer Geosciences Series, edited by C. Reigbar, H. Lühr, P. Schwintzer, and J Wicket, pp. 401–406, 2004.

  • Olsen, N., A model of the geomagnetic field and its secular variation for Epoch 2002 estimated from Ørsted data, Geophys. J. Int., 149, 453–461, 2002.

    Google Scholar 

  • Onwumechili, C. A., The Equatorial Electrojet, OPA Amsterdam, 1997.

    Google Scholar 

  • Stening, R. J., What drives the equatorial electrojet?, J. Atmos. Terr. Phys., 57(10), 1117–1128, 1995.

    Article  Google Scholar 

  • Stening, R. J. and D. E. Winch, Night-time geomagnetic variations at low latitudes, Planet. Space Sci., 35, 1523–1539, 1987.

    Article  Google Scholar 

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Correspondence to Heather McCreadie.

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McCreadie, H., Iyemori, T. Equatorial electrojet as a diagnostic tool of geomagnetic field models. Earth Planet Sp 58, 885–893 (2006). https://doi.org/10.1186/BF03351993

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