Evaluation of Solar Indices Used in Semi-Empirical Proxy Models

Space observations of total solar and UV irradiances have been conducted for about three decades. These are important for both understanding the physical mechanisms and causal relationships in the sun and also for their terrestrial climatic impacts. However, to establish their true role in climate change, irradiance time series covering a century, or longer time scales, are needed. Accordingly, considerable efforts have been put forward to constract semi-empirical proxy models for climate studies which necessarily depend on long-term solar indices to identify solar changes. In this paper, we compare various solar indices used for irradiance reconstructions and we will devote special attention how well they match the observed irradiance data over the last three solar cycles.