Artifacts in century-length atmospheric and coupled reanalyses over Antarctica due to historical data availability

Enabled by advances in data assimilation and the digitization of historical observations, atmospheric reanalysis products that span the entire twentieth century provide valuable gridded data over the sparsely observed high-latitude Southern Hemisphere. Here austral summer and winter surface pressure trends in three reanalyses are compared to trends in a statistically based pressure reconstruction, trends in atmospheric models without data assimilation, and estimates of uncertainty from the reanalyses. In austral summer during the early twentieth century, the reanalyses underestimate the depth of the circumpolar trough, leading to erroneously high pressure values over the region. Around 1950, a rapid increase in the number of assimilated pressure observations leads to a dramatic reduction in the reanalyses standard error and a spurious drop in the surface pressure. A more likely history of the surface pressure over this region is provided by the reconstruction, which is consistent with the model simulations without data assimilation.