| Author(s) and Co-Author(s) with Affiliation: Megha Anand(Manipal Centre for Natural Sciences, MAHE, Manipal - 576104, India), Atul Bhat(Manipal Centre for Natural Sciences, MAHE, Manipal - 576104, India), Durgesh Tripathi(Inter-University Centre for Astronomy and Astrophysics, Pune - 411007, India), Sreejith Padinhatteeri(Manipal Centre for Natural Sciences, MAHE, Manipal - 576104, India), A. N. Ramprakash(Inter-University Centre for Astronomy and Astrophysics, Pune - 411007, India), V. N. Nived(Inter-University Centre for Astronomy and Astrophysics, Pune - 411007, India), Janmejoy Sarkar(Max Planck Institute for Solar System Research, Gottingen, Germany -), Soumya Roy(Physical Research Laboratory, Ahmedabad - 380009, India), Rahul Gopalakrishnan(Inter-University Centre for Astronomy and Astrophysics, Pune - 411007, India), Rushikesh Deogaonkar(Inter-University Centre for Astronomy and Astrophysics, Pune - 411007, India), K. Sankarasubramanian(U R Rao Satellite Centre, Bengaluru - 560017, India) |
| Abstract: Solar UV variability governs key photochemical and radiative processes in Earth’s middle and upper atmosphere. The Mg II core-to-wing ratio (also known as "Mg II index") is a standard proxy for this variability, but existing records are Sun-as-a-star and lack spatial attribution. We report the first disk-resolved Mg II index, derived from Aditya-L1/SUIT full-disk imaging in four narrow bands around the Mg II lines (NB02, NB03, NB04, NB05). We construct pixel-level index maps from weighted wing and core signals, generate daily regional indices for plage, sunspots, and quiet Sun, and quantify their contributions to the disk average. The disk-integrated SUIT index co-varies with a standard composite, providing continuity with legacy proxies while, for the first time, attributing changes to specific magnetic features. We also quantify the NB03–NB04 spectral-response overlap using GOME and IRIS reference spectra convolved with SUIT responses; the inferred contribution is small (also feature-dependent) and does not alter the main findings. Taken together, this spatially explicit proxy enables new tests of irradiance reconstructions, connects feature evolution to global UV variability on rotational and longer timescales, and offers improved inputs for middle-atmosphere and space-weather applications. By establishing a stable, disk-resolved Mg II index proxy with routine synoptic coverage, SUIT provides new constraints that connect magnetic-feature morphology to UV irradiance variability, complementing existing proxy and semi-empirical models. |
