SST and SIC used in CORe: 

1) from 1950-1985: daily Hadley OIv2 data 
2) from 1986-present: daily OSTIA data
     step1: convert ostia from netcdf to grib format using the reference guide 
       https://www.cpc.ncep.noaa.gov/products/wesley/wgrib2/netcdf_2_grib_ostia.html
     step2: convert to CORe grid

For historical analysis from 1950-2023 on Gaea, CFS bufr files were used. 
For real-time update in later 2024, CDAS bufr files are used, as they contains slightly more 
observations due to a longer window.