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