The impact of the August 27, 1998, gamma-ray burst on the Schumann resonances

On 27 August 1998, at 10:22 UT, an extremely intense gamma ray Rare passed through the solar system. The gamma -ray burst lasted only 5 min and result ed in the ionization of a large portion of the Earth's night-side upper atm osphere to levels found normally only during the daytime. During this perio d we were continuously monitoring extremely low frequency (ELF) electromagn etic waves in the range 1-50 Hz, at a new monitoring site established in th e Negev Desert, Israel. We have analysed our ELF data, including the Schuma nn resonances, during this period, and no noticeable changes in the ELF sig nals are observed as a result of this event. This is very different to obse rvations in the VLF range that showed extreme changes in amplitude and phas e resulting from this gamma -ray burst. Theoretical modeling points to thre e factors that can explain the differences between the VLF and ELF signal r esponses. (i) different properties of the ELF and VLF signals within the ti me scale of the gamma -ray burst; (ii) different paths of these signals dur ing the event; and (iii) the different influences of the day/night asymmetr y on the propagation of ELF and VLF waves. (C) 2001 Elsevier Science Ltd. A ll rights reserved.