Evaluation of Reanalysis Products in the Arctic

Seasonal Anomaly Maps — each product compred to the ensemble median

Seasonal Trend Maps — seasonal trends of each variable

This work has been published in the Journal of Climate (Lindsay, R., M. Wensnahan, A. Schweiger, and J. Zhang, 2014: Evaluation of seven different atmospheric reanalysis products in the Arctic. J. Climate, DOI: 10.1175/JCLI-D-13-00014.1. )

Abstract

Atmospheric reanalyses depend on a mix of observations and model forecasts. In data-sparse regions such as the Arctic, the reanalysis solution is more dependent on the model structure, assumptions, and data assimilation methods than in data-rich regions. Applications such as the forcing of ice-ocean models are sensitive to the errors in reanalyses. Seven reanalysis datasets for the Arctic region are compared over the 30-year period 1981–2010: NCEP-R1, NCEP-R2, CFSR, 20CR, MERRA, ERA-Interim, and JRA-25. Emphasis is placed on variables not observed directly including surface fluxes and precipitation and their trends. The monthly averaged surface temperatures, radiative fluxes, precipitation, and wind speed are compared to observed values to assess how well the reanalysis data solutions capture the seasonal cycles. Three models stand out as being more consistent with independent observations: CFSR, MERRA, and ERA-Interim. A coupled ice–ocean model is forced with four of the datasets to determine how estimates of the ice thickness compare to observed values for each forcing and how the total ice volume differs among the simulations. Significant differences in the correlation of the simulated ice thickness with submarine measurements were found, with the MERRA products giving the best correlation (R=0.82). The trend in the total ice volume in September is greatest with MERRA (–4.1 103 km3 decade-1) and least with CFSR (–2,7 103 km3 decade-1).

Many additional seasonal intercomparison maps (many more than could be included in the publication) showing the median from the seven reanalyses and the deviations of each from the median are found at here . Both seasonal means and seasonal trends for the period 1981-2010 are shown. 34 different variables are included: surface fluxes, temperature, humidity, wind, precipitation, and pressure; layer heights and temperatures; and TOA radiative fluxes.