An assessment of ten ocean reanalyses in the polar regions

TLDR

Polar ocean and sea ice reanalysis products are widely used but their quality has not yet been systematically evaluated. The study establishes the Polar ORA Intercomparison Project to systematically evaluate polar reanalysis products. Ten polar ORAs were compared by analyzing their mean states for snow, sea ice, ocean transports, and hydrography, with many diagnostics performed for the first time. The ensemble mean of the ten ORAs shows smaller deviations from observations than individual products, suggesting offsetting biases, and is a useful tool for understanding polar marine conditions despite its limitations.

Abstract

Global and regional ocean and sea ice reanalysis products (ORAs) are increasingly used in polar research, but their quality remains to be systematically assessed. To address this, the Polar ORA Intercomparison Project (Polar ORA-IP) has been established following on from the ORA-IP project. Several aspects of ten selected ORAs in the Arctic and Antarctic were addressed by concentrating on comparing their mean states in terms of snow, sea ice, ocean transports and hydrography. Most polar diagnostics were carried out for the first time in such an extensive set of ORAs. For the multi-ORA mean state, we found that deviations from observations were typically smaller than individual ORA anomalies, often attributed to offsetting biases of individual ORAs. The ORA ensemble mean therefore appears to be a useful product and while knowing its main deficiencies and recognising its restrictions, it can be used to gain useful information on the physical state of the polar marine environment.