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Reanalysis is a scientific method for developing a comprehensive record of how weather and climate are changing over time. In it, observations and a numerical model that simulates one or more aspects of the Earth system are combined objectively to generate a synthesized estimate of the state of the system. A reanalysis typically extends over several decades or longer, and covers the entire globe from the Earth’s surface to well above the stratosphere. Reanalysis products are used extensively in climate research and services, including for monitoring and comparing current climate conditions with those of the past, identifying the causes of climate variations and change, and preparing climate predictions. Information derived from reanalyses is also being used increasingly in commercial and business applications in sectors such as energy, agriculture, water resources, and insurance.


Using a collaborative Wiki framework, the goal of is to facilitate comparison between reanalysis and observational datasets. Evaluative content provided by reanalysis developers, observationalists, and users; and links to detailed data descriptions, data access methods, analysis and plotting tools, and dataset references are available. Discussions of the recovery of observations to improve reanalyses is also a focus. The wiki framework encourages scientific discussion between members of and other reanalysis users. 



20CRv2c: NOAA and CIRES just released an improved version of the 20th Century Reanalysis, "2c", spanning 1851-2011. More details here.

JRA-55: The new Japanese 55-year Reanalysis (1958 to present) is available from multiple data providers.

ERA-20C: ECMWF just released their first reanalysis of the 20th century. More details here.

Pages and Meetings

AMS Annual Meeting Jan 10-14, 2016, New Orleans, Louisiana, USA.
        28 Conference on Climate Variability and Change
        session- 20th Century Reanalysis: Methods and Applications
        session- Earth System Climate Reanalysis: Low Frequency Variability and Trends
        Meeting details.

AGU Fall Meeting 14-18 December, 2015, San Francisco, California, USA.
        Session A042: Evaluating Reanalysis: What can we learn about past weather and climate?
        Session details.

SPARC Reanalysis Intercomparison Project (S-RIP) Workshop Oct 12-14, 2015, Paris, France
  Meeting details summary. Meeting website.

Animation and discussion of  2004/2005 and 1938 California flooding related to Atmospheric Rivers

Ana4MIPS: Providing access to netCDF formatted reanalysis data of selected variables, repackaged corresponding to the CMIP5 climate model output and Obs4MIPS standards at the Earth System Grid Federation (includes CFSR, MERRA, 20CR, JRA-25, ERA-Interim).