Representation of Climate in Reanalyses - An Intercomparison for Europe and North America

Abstract:

Atmospheric reanalysis data sets are a major tool to assess climate and its variability for past decades in a broad spectrum of applications. Nowadays, global reanalysis systems are available in third and fourth generation. They benefit from continuous improvements of numerical models and data assimilation schemes thus utilizing a growing number of observing systems. In the past decade, global reanalyses have been complemented by several regional reanalyses with enhanced horizontal resolution and appropriate model physics.

Due to the considerable technical overhead associated with the comparison of reanalyses, it is difficult for users to identify an optimal data set for their needs. Therefore, this presentation provides a comprehensive intercomparison of the representation of climate in various reanalyses. Four global reanalyses and three regional reanalyses over Europe and North America are compared with in-situ observations and for multiple regions on both continents to allow for a spatial differentiation. The focus lies on the representation of near-surface temperature and precipitation expressed through various climate indices.

The comparison shows that performances of the different reanalyses vary considerably depending on the parameter(s) of interest, the region and the type of aggregation. The main findings are that regional reanalyses provide added value especially with regard to precipitation. While ECMWF's newest reanalysis ERA5 is in better agreement with observations compared to the other global reanalyses for most climate indices over Europe, it is still outperformed by its predecessor ERA-Interim over North America.