Pacific decadal oscillation (PDO) 1935–2013.

The PDO is the leading principal component of the North Pacific monthly sea surface temperature. The annual measurements (black dotted line) are smoothed with a 13-year centered moving average filter (black solid line). The sinusoid (red dashed line) is a least squares fit to the moving average. The data are from the University of Washington's PDO website, http://jisao.washington.edu/pdo/.