Mandal, Sudip Max Planck Institute for Solar System Research, Max Planck Society;
Jha, B. K., Mandal, S., & Banerjee, D. (2019). Study of Sunspot Penumbra to Umbra Area Ratio Using Kodaikanal White-light Digitised Data. Solar Physics, 294(6): 72. doi:10.1007/s11207-019-1462-2.