Influence of solar terminator passages on Schumann resonance parameters

The Terminator Effect (TE) on extremely low frequency (ELF) electromagnetic waves or Schumann Resonances (SR) was investigated on the basis of observations during a number of years at different mid-latitude stations [Hollister (36.8degrees N, 121.5degrees W, SAO, USA), Mitzpe Ramon (30.5degrees N, 34.4degrees E, MR, Israel) and Nagycenk (47.6 N, 16.7 E, NC, Hungary)]. Definite shifts are observed in the SR magnetic and electric field characteristics during local sunrise and sunset. The terminator passage influences all magnetic field components at SAO, with more significant effects in the east-west component. At MR and NC stations notable effects were observed only in the vertical electric field. The TE is more pronounced in higher SR modes (14, 20 Hz) compared with the 8 Hz mode. Furthermore, the TE is more pronounced in the morning than evening, and more pronounced in winter than in summer. All these observations indicate that, in addition to diurnal-seasonal thunderstorm source motions, lateral ionospheric gradients across the terminator region have significant influences on ELF wave propagation. (C) 2004 Published by Elsevier Ltd.