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  • 1. Dahlgren, Hanna
    et al.
    Sundberg, Torbjörn
    Collier, Andrew B.
    Koen, Etienne
    Meyer, Stephen
    Solar flares detected by the new narrowband VLF receiver at SANAE IV2011In: South African Journal of Science, ISSN 0038-2353, E-ISSN 1996-7489, Vol. 107, no 9-10, p. 39-46Article in journal (Refereed)
    Abstract [en]

    A narrowband receiver was installed at the SANAE IV base in Antarctica to monitor specific very low frequency (VLF) radio signals from transmitters around the world. VLF waves propagating through the Earth-Ionosphere Waveguide are excellent probes of the varying properties of the lower region of the ionosphere. This paper describes the set-up of the narrowband system and demonstrates its capabilities with data from a set of solar flares on 08 February and 12 February 2010.

  • 2.
    Koen, Etienne J.
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Collier, Andrew B.
    SANSA Space Science, Hospital Street, Hermanus 7200, South Africa; School of Chemistry, University of KwaZulu-Natal, Durban, South Africa.
    Mid-latitude ionospheric signature of a weak solar flare in winter2013In: South African Journal of Science, ISSN 0038-2353, E-ISSN 1996-7489, Vol. 109, no 1-2, p. 83-87Article in journal (Refereed)
    Abstract [en]

    Measurements of the amplitude and phase of very low frequency transmitter signals were used to evaluate the effects on the ionosphere of a moderate intensity solar flare that occurred on 13 December 2007. These measurements were compared to modelled results from the Long Wave Propagation Capability code. The ionospheric effects were found to be delayed by ∼1 min with respect to the 0.1-0.8 nm solar X-ray flux.

  • 3. Oster, J.
    et al.
    Collier, A. B.
    Hughes, A. R. W.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lichtenberger, J.
    Spatial correlation between lightning strikes and whistler observations from Tihany, Hungary2009In: South African Journal of Science, ISSN 0038-2353, E-ISSN 1996-7489, Vol. 105, no 5-6, p. 234-237Article in journal (Refereed)
    Abstract [en]

    A whistler is a very low frequency (VLF) phenomenon that acquires its characteristics from dispersive propagation in the magnetosphere. Whistlers are derived from the intense VLF radiation produced in lightning strikes, which can travel great distances within the Earth-ionosphere waveguide (EIWG) before penetrating the ionosphere, and exciting a duct. Field-aligned ducts of enhanced plasma density guide the propagation from one hemisphere to the other. The location of the duct, relative to the strike that causes the whistler, is unknown. Whistler time series from Tihany, Hungary, have been cross-correlated with lightning data obtained from the World Wide Lightning Location Network (WWLLN). The results show that whistlers observed at Tihany originate mainly from lightning strikes in an area with a radius of approximately 1 000 km surrounding the magnetic conjugate point in the Indian Ocean just east of East London, South Africa. A clear diurnal distinction was seen in that the correlation is maximised when the whistler station and the source region are in darkness. This is believed to relate to the diurnal variation of the ionosphere, which becomes more transparent to VLF waves at night.

  • 4. Sundberg, K. Å. T.
    et al.
    Hughes, A. R. W.
    Collier, A. B.
    Eriksson, P. T. I.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Magnetic field oscillations at SANAE IV related to sudden increases in solar wind dynamic pressure2005In: South African Journal of Science, ISSN 0038-2353, E-ISSN 1996-7489, Vol. 101, no 12-nov, p. 539-543Article in journal (Refereed)
    Abstract [en]

    The magnetospheric response at times when sudden increases in the solar wind dynamic pressure cause terrestrial magnetic storms has been studied with data from the pulsation magnetometer at the South African Antarctic research base, SANAE IV. For solar wind events that lead to a sudden increase in the terrestrial magnetic field at Hermanus and Kakioka, related pulsations were found in the SANAE IV data. We studied seven solar wind events of special interest between 19 February 2003 and 18 February 2004. The events can be divided into two main pulsation groups: one group had a well-defined frequency and a duration of about 15 minutes, whereas the other had a less well-defined frequency content, longer duration and exhibited large amplitude fluctuations. The analysis confirms the conclusion that the measured response time of the magnetosphere to disturbances in the solar wind is broadly consistent with the propagation speed of magneto-hydrodynamic waves driven by solar wind dynamic pressure.

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