Abstract
Mesoscale sea surface temperature (SST) variability triggers mesoscale air–sea interactions and is linked to ocean subsurface mesoscale dynamics. The National Oceanic and Atmospheric Administration (NOAA) daily Optimum Interpolation SST (OISST) products, based on various satellite and in situ SST data, are widely utilized in the investigation of multi-scale SST variabilities and reconstruction of subsurface and deep-ocean fields. The quality of OISST datasets is subjected to temporal inhomogeneity due to alterations in the merged data. Yet, whether this issue can significantly affect mesoscale SST variability is unknown. The analysis of this study detects an abrupt enhancement of mesoscale SST variability after 2007 in the OISST-AVHRR-only version 2 and version 2.1 datasets (hereafter OI.v2-AVHRR-only and OI.v2.1-AVHRR-only). The contrast is most stark in the subtropical western boundary current (WBC) regions, where the average mesoscale SST variance during 2007–2018 is twofold larger than that during 1993–2006. Further comparisons with other satellite SST datasets (TMI, AMSR-E, and WindSAT) suggest that the OISST-AVHRR-only datasets have severely underestimated mesoscale SST variability before 2007. An evaluation of related documents of the OISST data indicates that this bias is mainly caused by the change of satellite AVHRR instrument in 2007. There are no corresponding changes detected in the associated fields, such as the number and activity of mesoscale eddies or the background SST gradient in these regions, confirming that the underestimation of mesoscale SST variability before 2007 is an artifact. Another OISST product, OI.v2-AVHRR-AMSR, shows a similar abrupt enhancement of mesoscale SST variability in June 2002, when the AMSR-E instrument was incorporated. This issue leaves potential influences on scientific research that utilize the OISST datasets. The composite SST anomalies of mesoscale eddies based on the OI.v2-AVHRR-only data are underestimated by up to 37% before 2007 in the subtropical WBC regions. The underestimation of mesoscale variability also affects the total (full-scale) SST variability, particularly in winter. Other SST data products based on the OISST datasets were also influenced; we identify suspicious changes in J-OFURO3 and CFSR datasets; the reconstructed three-dimensional ocean products using OISST data as input may also be inevitably affected. This study reminds caution in the usage of the OISST and relevant data products in the investigation of mesoscale processes.
Highlights
These results indicate that the OI.v2-Advanced Very High-Resolution Radiometer (AVHRR)-only (OI.v2-AVHRR-AMSR) data weakly estimate the strength of the mesoscale sea surface temperature (SST) variation in most subtropical oceans, especially the western boundary current (WBC) regions before 2007 (June 2002), due to an artifact in the data
We examine whether the TM 0 variance exhibits an abrupt increase in the WBC regions in the J-OFURO3 data and CFSR data
This study investigated the interannual variability of the intensity of mesoscale SST, which is represented by the mesoscale SST variance in the global ocean, in the four subtropical WBC regions (KE, GulfStream Extension (GSE), Agulhas Return Current (ARC), and Brazil–Malvinas Confluence (BMC)) for the period of
Summary
These eddies are ubiquitous in the global ocean and active in the subtropical western boundary currents (WBCs) and their extensions [1,12,13,14,15]. In addition to being action centers for the dynamic ocean circulation changes, the WBCs and their extensions are hotspots for thermodynamical interaction between SST anomalies (SSTAs) and the overlying atmosphere [13,19,20,21,22]. Such interaction is scale dependent [23]. SSTAs of mesoscale eddies cause surface turbulent heat flux anomalies and affect the stability of the atmospheric boundary layer [30,35,36,37], exerting imprints on cloud formation, cloud liquid water, and precipitation rate [37,38]
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