50 MHz Backscatter Observations in the Polar Cap Ionospheric E Region

  • C. Haldoupis
  • M. J. McKibben
  • J. A. Koehler
  • G. J. Sofko
Part of the NATO ASI Series book series (ASIC, volume 278)


Results of VHF Doppler measurements made at an invariant geomagnetic latitude near 77° are presented. The experiment was set up so that high resolution spectral measurements could be made from a common E region volume along two bistatic CW radio links at magnetic aspect angles of 9.5° and 13.5° from perpendicularity to the earth’s magnetic field. For the events considered in this study the evidence, based on K p index and meridional magnetograms, shows the backscatter region to be located mostly poleward of the auroral electrojet boundary inside the polar cap. The most striking feature of the data is the temporal morphology of the polar cap echo occurrence which differs from that in the auroral zone. In particular there is a complete absence of echoes at midnight and early morning hours, unlike the auroral zone where strong westward electrojet echoes are often present. The strongest and most frequently occurring echoes were observed for a few hours prior to midnight and were always associated with southward Hall drift motions. Comparison with ionosonde data shows a close connection between echo occurrence and the presence of a strong sporadic E s layer. Magnetometer and riometer data suggest that, at times, other factors, than electrojet currents and absorption, control the echo occurrence at these high latitudes. On the other hand, the Doppler spectral signatures of the echoes suggest the same instability mechanisms to be responsible for the generation of short scale irregularities in the polar cap as in the auroral zone. Finally, the results show the magnetic aspect control is not strong at 50 MHz. thus VHF coherent radars can be useful diagnostic tools in probing the lower ionosphere at polar cap regions.


Interplanetary Magnetic Field Doppler Spectrum Auroral Zone Auroral Oval Aspect Angle 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Acasofu, S.-I. and Chapman, S. (1972) Solar-Terrestrial Physics, University Press, Oxford.Google Scholar
  2. Bahnsen, A., Ungstrup, C., Falthammar, C.-G., Fahleson, U., Olesen, J. K., Primdahl, F., Spasnglev, F. and Pedersen, A. (1978) ‘Electrostatic waves observed in an unstable polar cap ionosphere’, J. Geophys. Res., 83, 5191–5197.ADSCrossRefGoogle Scholar
  3. Chubb, T. A. and Hicks, G. T. (1970) ‘Observations of the aurora in the far ultraviolet, from OGO 4’, J. Geophys. Res., 75,1290–1311.ADSCrossRefGoogle Scholar
  4. Fejer, B. G. and Kelley, M. C. (1980) ‘Ionospheric irregularities’, Rev. Geophys., 18, 401–454.ADSCrossRefGoogle Scholar
  5. Fejer, B. G. and Providakes, J. F. (1987) ‘High latitude E region irregularities: new results’, Phys. Scripta, Vol T 18, 167–178.CrossRefGoogle Scholar
  6. Fraser-Smith, A. C. (1982) ‘ULF/lower-ELF electromagnetic field measurements in the polar caps’, Rev. Geophys. Space Phys., 20, 497–512.ADSCrossRefGoogle Scholar
  7. Greenwald, R. A., Ecklund, W. L. and Balsley, B. B. (1975) ‘Radar observations of auroral electro jet currents’, 80, 3635–3641.Google Scholar
  8. Iialdoupis, C. (1989) ‘A review on radio studies of auroral E region ionospheric irregularities’, Ann. Geophysicae, 7.3.Google Scholar
  9. Haldoupis, C., Nielsen, E. and Goertz, C. K. (1982) ‘Experimental evidence on the dependence of 140 MHz auroral backscatter characteristics on ionospheric conductivity’, J. Geophys. Res., 87, 7666–7670.ADSCrossRefGoogle Scholar
  10. Haldoupis, C. and Sofko, G. J. (1976) ‘Doppler spectrum of 42 MHz CW auroral backscatter’, Can. J. Phys., 54, 1571–1584.ADSCrossRefGoogle Scholar
  11. Hultqvist, B. (1966) ‘Ionospheric Absorption of cosmic radio noise’, Space Sci. Rev.,5. 771–817.ADSGoogle Scholar
  12. Koehler, J. A., Sofko, G. J., Mehta, V., McNamara, A. G. and McDiarmid, D. R. (1985) ‘Observations of magnetic aspect effects in auroral radar backscatter’, Can. J. Phys., 63, 402–408.ADSCrossRefGoogle Scholar
  13. McNamara, A. G. (1972) ‘The occurence of radio aurora at high latitudes: The IGY period, 1957–1959’, Geophys. Publ., 29,135–149.Google Scholar
  14. Moorcroft, D. R. (1985) ‘An examination of radio auroral aspect sensitivity’, Can. J. Phys., 63, 1005–1012.ADSCrossRefGoogle Scholar
  15. Piggot, W. R. and Rawer, K. (1975) URSI handbook of ionogram interpretation and reduction, Elsvier Publ., Amsterdam.Google Scholar
  16. Primdahl, F., Olesen, J. K. and Spangslev, F. (1974) ‘Backscatter from a postulated plasma instability in the polar cap ionosphere and the direct measurement of a horizontal E region current’, J. Geophys. Res., 79, 4262–4268.ADSCrossRefGoogle Scholar
  17. Sandholt, P. E., Egeland, A., Holtet, J. A., Lybekk, B., Svenes, K. and Asheim, S. (1985) ‘Large- and small- scale dynamics in the polar cusp’, 90, 4407–4414.Google Scholar
  18. Sofko, G. J., Koehler, J. A., Haldoupis, C., McKibben, M. J. and McNamara, A. G. (1987) ‘Doppler radio observations of 3-meter irregularities in the polar cap E region’, J. Geophys. Res., 92, 1271–1276.ADSCrossRefGoogle Scholar
  19. Sofko, G. J., Koehler, J. A., Prikryl, P. and McDiarmid, D. R. (1985) ‘50-MHz auroral Doppler spectra dynamics during the Harang discontinuity’, Radio Sci., 20, 696–708.ADSCrossRefGoogle Scholar
  20. Tsunoda, R. T., Perreault, R. D. and Hodges, J. C. (1976) ‘Azimuthal distribution of HF slant E region echoes and its relationship to the polar cap electric field’, J. Geophys. Res., 81, 3834–3844.ADSCrossRefGoogle Scholar
  21. Unwin, R. S. (1972) ‘The radio aurora’, Ann. Geophys., 28(1), 111–127.Google Scholar

Copyright information

© Kluwer Academic Publishers 1989

Authors and Affiliations

  • C. Haldoupis
    • 1
  • M. J. McKibben
    • 2
  • J. A. Koehler
    • 2
  • G. J. Sofko
    • 2
  1. 1.Institute of Space and Atmospheric StudiesPhysics Department,University of CreteIraklion, CreteGreece
  2. 2.Physics DepartmentUniversity of SaskatchewanSaskatoonCanada

Personalised recommendations