Initial results from AWESOME VLF receivers: set up in low latitude Indian regions under IHY2007/UNBSSI program

Abstract

This article delineates preliminary results obtained from three newly set up very low frequency (VLF) radio receiver observation stations at low latitude Indian sites Allahabad (16.49°N), Nainital (20.48°N) and Varanasi (15.41°N), during 2007. These stations were set up by collaboration between the Indian Institute of Geomagnetism, Mumbai and Stanford University, USA under the International Heliophysical Year 2007/United Nations Basic Space Science Initiative (UNBSSI) program. VLF stations are part of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in extremely low frequency (ELF) and VLF bands. The new set up of VLF receiver is a marked improvement over the traditional recording and analysis systems in India. It provides additional facilities to study the VLF phenomena at low latitudes which were not studied earlier, like direction finding of events like whistlers, emissions, etc. and D-region ionospheric perturbation caused by the geophysical phenomena such as solar flares, lightning induced electron precipitations, cosmic gamma ray flares, terrestrial gamma rays flares, geomagnetic storm effect, etc. Simultaneous observation at multiple sites will provide opportunity to study in more detail the application of ELF/VLF data as earthquake precursors. Some of the initial results obtained from the preliminary analysis are presented to show the probing potentiality of ELF/VLF waves in ionosphere/magnetosphere studies.