An assessment of ten ocean reanalyses in the polar regions

Petteri Uotila,Jiping Xie,François Massonnet,Clément Bricaud,K Andrew Peterson,Antoine Barthélemy,J Carton ,Hugues Goosse,Takahiro Toyoda,Li Shi,Gilles Garric,Steffen Tietsche,Doroteaciro Iovino,Neven S Fučkar ,Marika Marnela,Davi Mignac,Remon Sadikni,Matthieu Chevallier,Vidar S Lien,Frank Kauker,Meri Korhonen,Keith Haines,Zhaoru Zhang

doi:10.1007/s00382-018-4242-z

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.

Highlights

Atmospheric reanalysis products, which consist of multidecadal meteorological model simulations with assimilated observations, have become an invaluable resource for researchers representing a wide range of disciplines
Ten ocean reanalyses (ORAs) show an overall agreement in the location of the sea-ice edge in the Arctic Ocean and along its margins (Figs. 2, S1 and S2), which can be attributed to sea-ice data assimilation and the constraint by the atmospheric forcing
A number of ORAs underestimate the presence of sea ice east of Greenland, and some underestimate sea-ice melt near the shelves, in the Kara Sea and in Baffin Bay

Summary

Introduction

Atmospheric reanalysis products, which consist of multidecadal meteorological model simulations with assimilated observations, have become an invaluable resource for researchers representing a wide range of disciplines. It is likely that these products will become as valuable as their atmospheric counterparts. An ocean analysis describes an ocean state valid for a particular time by a set of gridded oceanographic variables. An ocean analysis is generated by an analysis system consisting of a hydrodynamical or statistical model and an observation assimilation framework, for the purpose of initialising a forecast. During the analysis generation process, the forecast model background state is adjusted toward new observations. The amount of adjustment is denoted as the analysis increment, which quantify the impact of data assimilation in the analysis system (Cullather and Bosilovich 2012)

Methods

Results

Discussion

Conclusion