Analysis of large-scale ocean bottom pressure variability in the North Pacific

We use the leading empirical orthogonal functions (EOFs) of ocean bottom pressure (OBP) derived from an ocean model and the technique of EOF reconstruction to reduce noise in the large-scale OBP variations derived from the Gravity Recovery and Climate Experiment (GRACE). The subsequent OBP variations from the model and GRACE are then examined in the North Pacific between January 2003 and May 2007. Although annual and semiannual variations are similar, GRACE observes large interannual fluctuations poleward of 30 degrees, where OBP increases from a low of nearly 3 cm below normal in early 2003 to normal throughout 2004 and 2005, then an increase of nearly the same magnitude in 2006. These fluctuations have also been observed in OBP inferred from satellite altimetry corrected for steric variations computed from Argo float data. Since GRACE and steric-corrected altimetry are completely independent observations of OBP, we conclude that the model has errors or deficiencies in predicting the interannual OBP fluctuations in the North Pacific.