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Regional Arctic Reanalysis (RARE)


Although it only covers 5% of the World Ocean the Arctic Ocean/sea ice system plays key roles in controlling the humidity and temperature of the north polar atmosphere and thus influences the position, strength, and variability of the polar winds. These winds, in turn, supply the torque that drives ocean currents and the movement of sea ice. Wind-driven upwelling and wintertime cooling produces the deepwater that carries the imprint of the Arctic throughout the rest of the global ocean.

The Arctic Ocean/sea ice system is also a region of rapid anthropogenic change. While the ultimate cause is the increasing concentration of atmospheric gasses such as carbon dioxide (raising global net surface heating by ~1Wm-2) the rapidity of change in the Arctic is due to amplification by climate feedbacks. This change is most evident in the 40% reduction in the areal extent of summer sea ice cover since 1980. The NSF-supported development of eddy-resolving reanalyses beginning with the Regional Arctic Ocean/sea ice Reanalysis (RARE) is itself a step towards the broader goal of improving documentation and dynamical understanding of the global ocean/sea ice system and its roles in climate interactions/feedbacks.

Version 1 (RARE1) uses GFDL MOM5/SIS1 numerics with GEBCO 2014 bottom topography and ERA5 surface forcings on an eddy permitting quasi-isotropic horizontal grid (The southern boundary at 44.7°N has 8.2 km cells, while Fram Strait at 80°N is spanned by 1.7km cells). Continental discharge is constructed from historical gauge data. The main subsurface observation set is the World Ocean Database (WOD) of historical hydrographic profiles with updates through 2021 while surface data includes in-situ and satellite SST observations. For the cap poleward of 60°N WOD contains 477,000 casts that extend to at least 100m depth during 1980-2020. The gridded PIOMAS version 2.1 sea ice thickness estimates of Lindsay and Zhang are used to constrain sea ice. Data assimilation resembles that used in the global Simple Ocean Data Assimilation version 3 (SODA3). Ocean/sea ice output files are available at both 5dy and monthly resolution (regridded onto a regular grid). Development of RARE2 (RARE - the next generation) has begun.

The rare1.15.2 data sets are accessible here.

Reference: Carton, J. A., & Chepurin, G. A. (2022). RARE: the Regional Arctic Reanalysis, Journal of Climate (published online ahead of print 2022). Retrieved Feb 25, 2023, from https://journals.ametsoc.org/view/journals/clim/aop/JCLI-D-22-0340.1/JCLI-D-22-0340.1.xml

Credit: James Carton 2/23/2023