W. Suparta and  M. A. Mohd. Ali and  M. S. Jit Singh and  B. Yatim and  T. Motoba and  N. Sato and  A. Kadokura and  G. Bjornsson,  GPS TEC Variation Affected by the Interhemispheric Conjugate Auroral Activity on 21 September 2009.   journal   = {International Journal of Geological and Environmental Engineering}, [online]. World Academy of Science, Engineering and Technology.
    December 2011, vol. 60(12). 821 - 824
    [viewed 06 July 2020]. Available from: https://publications.waset.org/pdf/8568.