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Optimum Interpolation Sea Surface Temperature (OISST) v2.1

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The NOAA 1/4° daily Optimum Interpolation Sea Surface Temperature (or daily OISST) is an analysis constructed by combining observations from different platforms (satellites, ships, buoys and Argo floats) on a regular global grid. A spatially complete SST map is produced by interpolating to fill in gaps. The methodology includes bias adjustment of satellite and ship observations (referenced to buoys) to compensate for platform differences and sensor biases. This proved critical during the Mt. Pinatubo eruption in 1991, when the widespread presence of volcanic aerosols resulted in infrared satellite temperatures that were much cooler than actual ocean temperatures (Reynolds 1993). Starting from April 1, 2020, NCEI released a new version, OISST v2.1, to replace OISST v2. OISST v2 had been stopped on April 26, 2020 due to unavailable input data to it.

Currently OISST v2.1 data are available from Sept 1, 1981 onward and updated nominally daily. The new version has significant quality improvement for data starting from January 1, 2016 onward - see below for more details. For the data from September 1981 to December 2015, data for SST and SST anomaly are the same as v2 but format was updated from netCDF3 to netCDF4 with updated metadata in v2.1. 

  • Major improvements from v2 to v2.1 for January 2016 onward include: 1) In-Situ ship and buoy data changed from the NCEP Traditional Alphanumeric Codes (TAC) to the NCEI merged TAC + Binary Universal Form for the Representation (BUFR) data, with large increase of buoy data included to correct satellite SST biases; 2) Addition of Argo float observed SST data as well, for further correction of satellite SST biases; 3) Satellite input from the METOP-A and NOAA-19 to METOP-A and METOP-B, removing degraded satellite data; 4) Revised ship-buoy SST corrections for improved accuracy; and 5) Revised sea-ice-concentration to SST conversion to remove warm biases in the Arctic region (Banzon et al. 2020). 
  • OISST is an analysis constructed by combining observations from different platforms (satellites, ships, buoys and Argo floats) on a regular global grid. A spatially complete SST map is produced by interpolating to fill in gaps. The methodology includes bias adjustment of satellite and ship observations (referenced to buoys) to compensate for platform differences and sensor biases. This proved critical during the Mt. Pinatubo eruption in 1991, when the widespread presence of volcanic aerosols resulted in infrared satellite temperatures that were much cooler than actual ocean temperatures (Reynolds 1993).

Additional Data

Three other maps at the same 1/4° spatial resolution complement the daily OISST:

  • Anomalies (i.e., the daily OISST minus a 30-year climatological mean) represent departures from "normal" or average conditions. Computation of several climate indices, such as the El Niño index, utilize SST anomalies.
  • The error field provides a measure of confidence or quality, allowing users to exclude (using a threshold) or to minimize (using weights) the impact of daily OISST values with greater interpolation errors.
  • The seven-day median of daily sea ice concentrations serves as the basis for proxy SSTs in the marginal ice zone, where observations are lacking. The proxy SST allows interpolation of temperatures from the open ocean to the seasonal sea ice margin.