Diurnal Variation of VLF Radio Wave Signal Strength at 19.8 and 24 kHz Received at Khatav India (16o46ʹN, 75o53ʹE)

Abstract

The period from August 2009 to July 2010 was considered as a solar minimum period. In this period, solar activity like solar X-ray flares, solar wind, coronal mass ejections were at minimum level. In this research, it is focused on detailed study of diurnal behavior of VLF field strength of the waves transmitted by VLF station NWC Australia (19.8 kHz) and VLF station NAA, America (24 kHz). This research was carried out by using VLF Field strength Monitoring System located   at Khatav India (16^o46ʹN, 75^o53ʹE) during the period August 2009 to July 2010. This study explores how the ionosphere and VLF radio waves react to the solar radiation. In case of NWC (19.8 kHz), the signal strength recording shows diurnal variation which depends on illumination of the propagation path by the sunlight. This also shows that the signal strength varies according to the solar zenith angle during daytime. In case of VLF signal transmitted by NAA at 24 kHz, the number of sunrises and sunsets are observed in VLF signal strength due to the variations of illumination of the D-region during daytime.  In both the cases, the signal strength is more stable during daytime and fluctuating during nighttime due to the presence and absence of D-region   during daytime and nighttime respectively.

Keywords: VLF field strength, diurnal variation, ionosphere, solar zenith angle