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Abstract

Halos are brief diffuse glows that often precede sprites caused by intense positive lightning discharges [1]. Halos are rarely observed with low-light video cameras from the ground as a result of their short lifetimes ~1-2 ms and their faint luminosities which can be observed from space [2,3]. Here we report numerous optical observations of halos with a low-light video camera at the Square Kilometre Array (SKA) operations centre near Carnarvon in South Africa. It is found that the halos can be classified in four categories, i.e., (1) pure halos without sprites, (2) halos with a few column sprites of varying lengths, (3) halos with fully developed sprites and (4) halos with sprite groups. These optical observations are paralleled by waveform recordings of electric field strengths transmitted by the halo producing lightning discharges which are recorded with a wideband digital low frequency (~4 Hz – 400 kHz) radio receiver. One halo was recorded in all six electromagnetic field components, E_z, E_x, E_y, B_z, B_x, and B_y. The waveform exhibits many arrivals of consecutive sky waves and a detailed analysis shows that the halo is paralleled by two consecutive radio pulses that are attributed to cloud-to-ground and intracloud lightning. These findings offer new insights into the characteristics of halos and their relationship with lightning discharges. References[1] Barrington-Leigh et al., Journal of Geophysical Research, 2001, doi:10.1029/ 2000JA000073.[2] Lu et al., Geophysical Research Letters, 2018, doi: 10.1029/2018GL079594. [3] Perez-Invernon et al., Journal of Geophysical Research, 2018, doi:10.1029/2018JD029053.