An Evaluation of the Performance of the Twentieth Century Reanalysis Version 3

The performance of a new historical reanalysis, the NOAA-CIRES-DOE Twentieth Century Reanalysis version 3 (20CRv3), is evaluated via comparisons with other reanalyses and independent observations. This dataset provides global, 3-hourly estimates of the atmosphere from 1806 to 2015 by assimilating only surface pressure observations and prescribing sea surface temperature, sea ice concentration, and radiative forcings. Comparisons with independent observations, other reanalyses, and satellite products suggest that 20CRv3 can reliably produce atmospheric estimates on scales ranging from weather events to long-term climatic trends. Not only does 20CRv3 recreate a best estimate of the weather, including extreme events, it also provides an estimate of its confidence through the use of an ensemble. Surface pressure statistics suggest that these confidence estimates are reliable. Comparisons with independent upper-air observations in the Northern Hemisphere demonstrate that 20CRv3 has skill throughout the twentieth century. Upper-air fields from 20CRv3 in the late twentieth century and early twenty-first century correlate well with full-input reanalyses, and the correlation is predicted by the confidence fields from 20CRv3. The skill of analyzed 500-hPa geopotential heights from 20CRv3 for 1979-2015 is comparable to that of modern operational 3-4-day forecasts. Finally, 20CRv3 performs well on climate time scales. Long time series and multidecadal averages of mass, circulation, and precipitation fields agree well with modern reanalyses and station- and satellite-based products. 20CRv3 is also able to capture trends in tropospheric-layer temperatures that correlate well with independent products in the twentieth century, placing recent trends in a longer historical context.

Automated summary

The NOAA-CIRES-DOE Twentieth Century Reanalysis version 3 (20CRv3) provides reliable global atmospheric estimates from 1806 to 2015 by assimilating surface pressure observations and prescribing sea surface temperature, sea ice concentration, and radiative forcings. The dataset exhibits good skill in producing weather estimates and confidence through ensemble methods, performing well on various scales from weather events to long-term climate trends. Comparisons with independent observations and upper-air fields demonstrate the ability of 20CRv3 to capture trends in atmospheric variables and exhibit skill comparable to modern operational forecasts.