1. CSIR-National Geophysical Research Institute, Hyderabad 500007, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India; and Imo State University Owerri, Department of Physics, Owerri 460108, Nigeria. (corresponding author)
2. CSIR-National Geophysical Research Institute, Hyderabad 500007, India and Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India.