A time series of mean global skin SST anomaly using data from ATSR-2 and AATSR

A near-continuous time series of global mean, skin SST anomaly has been calculated for 1995 to 2011, based on the first consistently processed data set for the Along Track Scanning Radiometer(s) or ATSRs. The ATSR multi-mission Version 2.0 (ESA_V2) archive is used to derive level 3 averaged skin SSTs for ATSR-2 and AATSR consistently for both sensors using a standard operational-like processor. Data are then gridded, aligned between sensors and a final anomaly time series derived relative to a climatological average calculated, for each month, from the standard ATSR data for the same period; the process strongly reduces global mean and spatially varying biases. The ATSR-2 to AATSR SST relative bias is obtained by analysing the overlap period (July 2002 to June 2003) between the two sensors. Before alignment, the average relative bias between ESA_V2 SST data sets from the two instruments is + 0.03 K for the dual-view, three channel SST, with a small but linear relation to water vapour in the differences between ATSR-2 and AATSR. Post-alignment, the residual average relative bias is + 0.007 K. The sampled area for the final time series using the ESA_V2 data extends from 60° N to 65° S; it is recommended that sampling areas be always provided for time series of data for climate. The uncertainty on the monthly mean global SST anomaly is estimated to be 0.014 K for ATSR-2 and 0.011 K for AATSR which are comparable to the uncertainties on monthly global average in situ data sets in the equivalent time period.