Reconstructing Large-scale Variability from Palaeoclimatic Evidence by Means of Data Assimilation Through Upscaling and Nudging(DATUN)

Summary

This chapter describes a newly developed approach for extracting the climate signal from proxy records, termed DATUN (Data Assimilation Through Upscaling and Nudging).

The first half of the paper describes the development of an estimate of the strength of the Austral Summer Antarctic Oscillation using station sea level pressure records for the period 1878–1985, the first to our knowledge. To extend this record further back, a estimate using tree-ring chronologies back to 1743 has also been undertaken. Comparison of the two estimates shows moderate agreement on interannual and decadal timescales, but the comparison also points towards the inherent uncertainties of proxy-based climate reconstructions.

The background to, and theory behind, assimilation of large-scale climate patterns in general circulation models using pattern nudging are then explained. First results of nudging towards prescribed states of the Arctic Oscillation are shown.