Kushal Kumar Mahajan earned his BSc degree (1957) from the University of Jammu and Kashmir and MSc (1959) from Banaras Hindu University, after which he joined the National Physical Laboratory (NPL), New Delhi in the Radio Science Division and worked under the supervision of AP Mitra to obtain his PhD degree from Banaras Hindu University (BHU), Varanasi. He worked as a post-doctoral Research Associate (1965-67) at Cornell University's incoherent scatter Radar Facility (installed at Arecibo, Puerto Rico) on ionospheric temperatures and densities, and also at the Goddard Space Flight Centre, Greenbelt (1967-69) as an NRC-NASA resident Research Associate, again on ionospheric temperatures and densities measured by the Langmuir probe on rockets and satellites. He returned to NPL (1969) where he worked for the next 30 years in the area of upper atmosphere/ionosphere of the earth and other planets. He headed the Radio and Atmospheric Sciences Division, NPL, for several years before he retired in 1999.
Academic and Research Achievements: Mahajan worked on the dynamics of the ionospheric F-region and determined the vertical drift velocities from ionosonde measurements. These velocities were found to be consistent with those obtained later with the highly sophisticated incoherent scatter radar technique. Mahajan was the first to discover the role of plasma densities in controlling the temperature of electrons in the ionosphere and this work proved very useful in the improvement of International Reference Ionosphere model. He used the Pioneer-Venus direct ionospheric measurements at the planet Venus and identified the crucial role played by the neutral atmosphere during highly disturbed space weather conditions. At NPL, Mahajan, along with his students, used the newly built MST radar facility at Tirupati, obtained new results on K-H instability at stratospheric altitudes and detected quasi-periodic echoes from ionospheric irregularities, for the first time, at a tropical station, Tirupati. He has published 135 research papers in refereed journals and mentored several PhD students as well as post-doctoral Research Associates.
Other Contributions: Mahajan started a new group on "Ionospheres of Inner and Outer Planets" at NPL which did pioneering work on the ionospheres of magnetic planets Jupiter and Saturn (equatorial anomalies) and on the non-magnetic planets Venus and Mars (solar wind interaction). As Head, Radio and Atmospheric Sciences Division, Mahajan, in association with Dr AP Mitra, turned the Division into a major centre for global change research. A Regional Research Centre for South Asia on IGBP at NPL and a Free Air Carbon Dioxide Enrichment (FACE) facility at the IARI, New Delhi were set up during his tenure as Head of the Division which are doing excellent work on global change. He has guest edited special issues of Indian Journal of Radio & Space Physics, Advances in Space Research and Mapan. He was on the Editorial Board of Indian Journal of Physics and Indian Journal of Radio & Space Physics and has been member of several scientific committees connected with solar terrestrial physics.
Awards and Honours: Mahajan is a recipient of Om Prakash Bhasin Award (1994). He was elected as a Fellow of Indian Geophysical Union (1987) and Indian Academy of Sciences, Bangalore (1991).