Cold wintertime air masses over Europe: where do they come from and how do they form?
Data sets
ERA5 hourly data on single levels from 1940 to present https://doi.org/10.24381/cds.adbb2d47
NAO index https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml
AO index https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii
GBI index https://psl.noaa.gov/gcos_wgsp/Timeseries/Data/gbi.day.data