A pseudoproxy assessment of data assimilation for reconstructing the atmosphere-ocean dynamics of hydroclimate extremes

Climate of the Past | Steiger & Smerdon [2017]

Abstract

Because of the relatively brief observational record, the climate dynamics that drive multi-year to centennial hydroclimate variability are not adequately characterized and understood. Data assimilation(DA)-based paleoclimate reconstructions optimally fuse paleoclimate proxies with the dynamical constraints of climate models, thus providing a coherent dynamical picture of the past. Therefore DA is an important new tool for elucidating the mechanisms of hydroclimate variability over the last several millennia. But DA has so far remained an untested tool for global hydroclimate reconstructions. Here we explore whether or not DA can be used to skillfully reconstruct global hydroclimate variability along with the driving climate dynamics. Through a set of realistic pseudoproxy experiments we find that an established DA reconstruction approach can indeed be used to reconstruct hydroclimate at both annual and seasonal time scales. We find that temperature and hydroclimate variables are best reconstructed near the proxy sites; in particular for tree rings, we find that hydroclimate reconstructions depend critically on moisture-sensitive trees, while temperature reconstructions depend critically on temperature-sensitive trees. Real-world DA-based reconstructions will therefore likely require a spatial mixture of temperature and moisture sensitive trees to reconstruct both temperature and hydroclimate variables. Additionally, we illustrate how DA can be used to elucidate the dynamical mechanisms of drought with two examples: we examine the tropical drivers of multi-year droughts in the North American Southwest and in equatorial East Africa. This work thus provides a foundation for future DA-based hydroclimate reconstructions using real proxy networks, while also highlighting the utility of this important tool for hydroclimate research.

Full text can be found here.

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