SunRISE - Application of Spectral Synthesis to the Study of Solar Visible, UV, EUV and Infrared Variability

University Corporation For Atmospheric Res, Boulder CO

Investigators

Abstract

The investigators will work to understand the physical origins of solar radiative variability. The main effort is to utilize semi-empirical models of the solar atmosphere to represent features on the solar surface and, where discrepancies are discovered, redefine the models. The investigators will then determine the effect of the distribution of surface features on irradiance and combine the information with spectral synthesis lines and broad spectral bands so as to compute spectral and total irradiance for a particular state of the Sun. Ultimately, the investigators seek to determine the most efficient measurements to make in the future in order to take advantage of the basic redundancy in the solar spectrum. The aim of the RISE program is to improve physical understanding of present, past, and future radiative output variations in the extreme ultraviolet (EUV), ultraviolet (UV), visible and infrared. In a practical sense, spectrum synthesis gives insight into the reliability of the use of surrogates (also known as proxies) to estimate total and spectral irradiance in the absence of direct measurements of appropriate accuracy. This exploitation of the natural redundancy and coherence in the solar spectrum can lead to more efficient measurement and analysis programs. Previous work of the investigators illustrated the importance of the evolution and spatial distribution of both plage and network (i.e. magnetic flux emergence) in determining the detailed time variability of irradiance. This work also revealed the sensitivity of the continuum intensity variation to structures deeper in the photosphere. The continuing speculation of a link between solar and climate variability on timescales longer than a decade raises the important issue of changes in the color of the solar spectrum due to variability of lines and continuum. An accurate theoretical estimate of the total solar irradiance and the shape of the solar radiation spectrum are essential to climate studies.