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Meehl, GA, Hu AX, Santer BD, Xie SP.  2016.  Contribution of the Interdecadal Pacific Oscillation to twentieth-century global surface temperature trends. Nature Climate Change. 6:1005-1008.   10.1038/nclimate3107   AbstractWebsite

Longer-term externally forced trends in global mean surface temperatures (GMSTs) are embedded in the background noise of internally generated multidecadal variability(1). A key mode of internal variability is the Interdecadal Pacific Oscillation (IPO), which contributed to a reduced GMST trend during the early 2000s(1-3). We use a novel, physical phenomenon-based approach to quantify the contribution from a source of internally generated multidecadal variability-the IPO-to multidecadal GMST trends. Here we show that the largest IPO contributions occurred in its positive phase during the rapidwarming periods from 1910-1941 and 1971-1995, with the IPO contributing 71% and 75%, respectively, to the difference between the median values of the externally forced trends and observed trends. The IPO transition from positive to negative in the late-1990s contributed 27% of the discrepancy between model median estimates of the forced part of the GMST trend and the observed trend from 1995 to 2013, with additional contributions that are probably due to internal variability outside of the Pacific(4) and an externally forced response from small volcanic eruptions(5). Understanding and quantifying the contribution of a specific source of internally generated variability-the IPO-to GMST trends is necessary to improve decadal climate prediction skill.

Wang, LY, Liu QY, Xu LX, Xie SP.  2013.  Response of mode water and Subtropical Countercurrent to greenhouse gas and aerosol forcing in the North Pacific. Journal of Ocean University of China. 12:222-229.   10.1007/s11802-013-2193-x   AbstractWebsite

The response of the North Pacific Subtropical Mode Water and Subtropical Countercurrent (STCC) to changes in greenhouse gas (GHG) and aerosol is investigated based on the 20th-century historical and single-forcing simulations with the Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3). The aerosol effect causes sea surface temperature (SST) to decrease in the mid-latitude North Pacific, especially in the Kuroshio Extension region, during the past five decades (1950-2005), and this cooling effect exceeds the warming effect by the GHG increase. The STCC response to the GHG and aerosol forcing are opposite. In the GHG (aerosol) forcing run, the STCC decelerates (accelerates) due to the decreased (increased) mode waters in the North Pacific, resulting from a weaker (stronger) front in the mixed layer depth and decreased (increased) subduction in the mode water formation region. The aerosol effect on the SST, mode waters and STCC more than offsets the GHG effect. The response of SST in a zonal band around 40A degrees N and the STCC to the combined forcing in the historical simulation is similar to the response to the aerosol forcing.