Sub-Polar Gyre Index

We followed the method of Häkkinen and Rhines (2004) to calculate the Sub-Polar Gyre Index, which has been defined as the first Principal Component (PC1) of an Empirical Orthogonal Function Analysis (EOFA) of the sea level anomaly field in the North Atlantic.
Please note that new versions of the Sub-Polar Gyre Index will be added. Please include the resource version number in citation, and use the most recent version.