Evaluation of the initial NOAA AVHRR GAC SST reanalysis version 2 (RAN2 B01)

Under the NOAA AVHRR GAC Reanalysis project (RAN), a global dataset of consistent sea surface temperature (SST) retrievals from 1981-on will be created from multiple NOAA AVHRRs using the ACSPO system. Following release of RAN1 dataset in 2016, the initial RAN2 Beta 01 (“RAN2 B01”) dataset was produced from NOAA-07, 09, 11, 12, 14, 15 and 16 from 1981-2003. This paper evaluates the initial RAN2 B01 dataset and compares it with two other SST datasets, the NOAA-NASA Pathfinder v5.3 (“PF”) and ESA CCI v2.1 (“CCI”). The time series of monthly global biases and standard deviations with respect to uniformly quality controlled in situ SSTs, and clearsky fractions (percent of SST pixels to the total ice-free ocean) are compared. ‘Skin’ and ‘depth’ SSTs, only available in RAN and CCI data sets, and sensitivity of ’skin’ SST to true SST, are also compared. The RAN B01 outperforms PF. Compared to CCI, it generally delivers more clear-sky observations, often with a better accuracy and precision for both ‘skin’ and ‘depth’ SSTs. The sensitivity to true SST is lower and more variable in RAN2 B01, than in CCI. The RAN2 B01 performance following large volcanic eruptions needs improvements.