The 2nd NOAA AVHRR GAC SST Reanalysis (1981-2022)

Short abstract

The 2^nd SST reanalysis (RAN2) was created from 4km GAC data of the AVHRR instruments, flown onboard ten NOAA satellites from September 1981 – present, with the NOAA Advanced Clear-Sky Processor for Oceans (ACSPO) enterprise system. A number of features of the RAN2 SST make it different from existing AVHRR GAC reanalyzes. The data set includes “Subskin” SST, highly sensitive to true skin SST, and “Depth” SST, agreeing much closer with in situ SST. Both SSTs are retrieved in a full ~3,000 km AVHRR swath. The long-term AVHRR calibration trends are compensated for by daily recalculation of the regression coefficients using matchups with in situ SSTs collected within moving time windows; shorter-term biases are minimized on a monthly basis by correction of the regression offsets from 31-day windows. Calibration coefficients from L1B data, corrupted by Sun impingements on the sensor, are corrected by interpolation between the unaffected parts of the orbit. Stray light in the Earth view pixels is detected by the nighttime signal in the AVHRR band 2 and screened out. Regional cold SST biases, caused by volcanic aerosol after major eruptions, are mitigated by more conservative cloud screening, only applied in the affected latitudinal bands. The RAN2 SST is available at NOAA CoastWatch, https://coastwatch.noaa.gov/cw/satellite-data-products/sea-surface-temperature/acspo-avhrr-gac.html in swath L2P (144 10-min granules per 24hr interval), and two 0.02° gridded formats: uncollated (L3U; also 144 granules/24hr) and collated (L3C; two global maps per 24hr, for day and night). The presentation describes the major features of the RAN2 SST and evaluates its performance.