Editing IPCC:AR6/WGI/Chapter-Atlas (section)

==== Atlas.1.4.2 Reanalysis ====

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There are currently many atmospheric reanalysis datasets with different spatial resolution and assimilation algorithms (see [[IPCC:Wg1:Chapter:Annex-i|Annex I]] and [[IPCC:Wg1:Chapter:Chapter-1#1.5.2|Section 1.5.2]] ). There are also substantial differences among these datasets due to the types of observations assimilated into the reanalyses, the assimilation techniques that are used, and the resolution of the outputs, amongst other reasons. For example, 20CR ( [[#Slivinski--2019|Slivinski et al., 2019]] ) only assimilates surface pressure and sea surface temperature (SST) to achieve the longest record but at relatively low resolution, while ERA-20C ( [[#Poli--2016|Poli et al., 2016]] ) only assimilates surface pressure and surface marine winds. At the other extreme, very sophisticated assimilation systems using multiple surface, upper air and Earth observation data sources are employed, for example ERA5 ( [[#Hersbach--2020|Hersbach et al., 2020]] ) and JRA-55 ( [[#Harada--2016|Harada et al., 2016]] ), which also have much higher resolutions. Most reanalysis datasets cover the entire globe, but there are also high-resolution regional reanalysis datasets which provide further regional detail ( [[#Kaiser-Weiss--2019|Kaiser-Weiss et al., 2019]] ).

The Atlas and Interactive Atlas use information from ERA5 and from the bias-adjusted version WFDE5 ( [[#Cucchi--2020|Cucchi et al., 2020]] ) which is combined with ERA5 information over the ocean and used as the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) observational reference dataset W5E5 ( [[#Lange--2019b|Lange, 2019b]] ). This reference is also used in the Atlas for model evaluation ( [[#Atlas.1.4.4|Atlas.1.4.4]] ) and for bias-adjusting model outputs ( [[#Atlas.1.4.5|Atlas.1.4.5]] ).

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