BRARGAVA, BN, A YACOB, and DRK RAO. “A Filter Analysis of Magnetic Activity Index Ap for 1932-33 and 1952-53”. MAUSAM 19, no. 3 (July 1, 1968). Accessed September 19, 2024. http://103.215.208.102/index.php/MAUSAM/article/view/5677.