Comparison between variations in solar UV radiation and sunspot parameters with Mg II daily index as a proxy

Abstract

Solar UV radiation influence the Earth’s climate and upper atmosphere. The UV emission from the Sun modulates with the sunspot cycle with an 11-year periodicity. The variations in UV, EUV, and X-rays emission are significant during the solar cycle evolution compared to the visible part of the spectrum. The h & k lines of the Mg II spectra emitted from the chromosphere represent the solar UV variability. The sunspot’s magnetic fields and dynamics are responsible for the UV and EUV emissions from the solar chromosphere and corona. This paper compares the Mg II core-to-wing ratio of the h & k lines observed at 278 nm wavelength (obtained from Solar Backscattered Ultraviolet Spectrograph (SBUV) instrument onboard the NOAA satellite) with the sunspot area parameter obtained from Royal Greenwich Observatory. When the sunspot group area is small, there is a linear relationship between the sunspot group area and the Mg II index. But a non-linear relationship between the two is observed for the large sunspot group area. There is no phase delay between the appearance of sunspot groups on the solar photosphere and the emission from the Mg II doublet. Apart from 11-year periodicity, we observed common 4.7, 3.2, and 2.2-year periodicity in both the data sets, suggesting the Mg II index is related to the sunspot parameters.