A North Atlantic Ocean Observing System for Detecting Upper Layer Temperature Variability at Decadal Time-scales: The Past, Present, and Future

The expendable bathythermograph (XBT) is an oceanographic instrument that provides temperature profilesof the upper ocean (500m to 800m). XBT's have been used since the late 1960's in both a research and monitoring mode. In the monitoring mode,they are typically launched from the same commercial vessels that provide the atmospheric data needed to initialize 'high-seas' forecast models. Previous studies considering only sea surface temperature(SST) and sea level pressure (SLP) in the North Atlantic used a canonical correlation analysis (CCA) to characterize possible coupled modes of air-sea interaction. The CCA results included a decadal correlation between SST and SLP. The spatial characteristics of this mode included an NAO-like dipole in SLP and a Gulf Stream mode in SST (i.e., maximum amplitude of the SST mode was located over the Gulf Stream in the western subtropical Atlantic). The XBT provides data deeper into the water column (400m). CCA of the subsurface temperature data with SLP over the 30 year period of XBT data, show correlations at similar decadal time-scales and Gulf Stream-like spatial patterns. These results are compared to results from various coupled General Circulation Models to provide a dynamical framework to analyze the data. New oceanographic sampling strategies have been designed and are being implemented to continue monitoring of these signals as well as to provide the data needed to initialize climate forecast models.