National Oceanic and Atmospheric Administration
https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml

National Oceanic and Atmospheric Administration
https://www.psl.noaa.gov/data/gridded/data.ncep.reanalysis.html

National Oceanic and Atmospheric Administration
https://www.psl.noaa.gov/data/gridded/data.noaa.ersst.v5.html