Jilani, Saifuddin Ahmed, Kinza Khursheed, and Kamran Mukhtar. 2021. “Comparative Study of F2–Layer Critical Frequency: Solar Cycle 22 : F2–Layer Critical Frequency ”. Proceedings of the Pakistan Academy of Sciences: A. Physical and Computational Sciences 55 (1):35-46. http://ppaspk.org/index.php/PPAS-A/article/view/199.