COMPARATIVE STUDY TOWARDS MILLENNIUM REANALYSIS BY DATA ASSIMILATION USING ISOTOPE RATIOS OF PROXIES

Abstract

 Recently, data assimilation has been introduced into climate reconstruction. In this study, we conducted several experiments with different prior estimates in order to reconstruct climate change over the last millennium by data assimilation using oxygen isotope ratios of proxies. The results show global surface air temperature decline after the large-scale volcanic eruptions in the past and the global distribution of surface air temperature difference between the Medieval Warm Period (MWP) and the Little Ice Age (LIA). The temperature decrease after the volcanic eruptions was confirmed by results of other studies using data assimilation. On the other hand, the global distribution of surface air temperature difference (MWP-LIA) was different from the other studies, mainly in the tropical Pacific. In this study, proxy models corresponding to process of isotopic variation are used, while statistical proxy models are used in the other studies. As well as the climate models and proxies used for data assimilation, it is suggested that the difference of the methods is reflected in the results.