DR. PRADEEP KAYSHAP

Mg II core-to-wing ratio is a useful index of UV variability, which has been measured since 1978 using data from various satellites. However, it has been done only for Sun-as-a-Star observations. For the first time, this index is measured for spatially resolved Sun using the observations recorded by the IRIS. The aim of this work is to understand the behavior of Mg II index in various solar features such as active region, umbra, penumbra, faculae, plage as well as quiet-Sun (QS), which will provide a better understanding of the solar UV variation and help model the Sun- climate relations. Using IRIS high resolution observations of Mg II lines, we have found that Mg II index of faculae is almost double in comparison to that of the QS index. Moreover, the Mg II index in umbra is slightly lower in comparison to that of QS index. Index of faculae is decreased by an amount of 21% within the time period of 9 days, which suggest that emission from the faculae is decreasing with time, due to temporal evolution. However, emission from QS regions is almost constant over time. Center-to- limb effect is present in Mg II index for each solar feature. Using these spatially dependent index values, we have calculated the on-average Mg II index from whole solar disk that is compared with previously reported index values. These results will be used for dealing and understanding the observations taken from the Solar Ultraviolet Imaging Telescope (SUIT) on board Aditya-L1.