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Gao, WD, Li PL, Xie SP, Xu LX, Liu C.  2016.  Multicore structure of the North Pacific subtropical mode water from enhanced Argo observations. Geophysical Research Letters. 43:1249-1255.   10.1002/2015gl067495   AbstractWebsite

Seventeen Argo profiling floats with enhanced vertical and temporal sampling were deployed in the Kuroshio recirculation gyre in the western North Pacific in late March 2014. The Subtropical Mode Water (STMW) observed in many profiles displays a multicore structure with more than one minima in potential vorticity (PV), corroborated by vertical covariations in apparent oxygen utilization (AOU). These cores are classified into four submodes according to density and AOU. The submode waters are typically 100m thick, in which PV varies by 1x10(-10)m(-1)s(-1) and AOU by 10 mu mole/kg. The STMW multicore structure is most frequently observed in spring, gradually taken over by single-core profiles into summer. The seasonal evolution is suggestive of vertical mixing, especially in STMW of lower density.

Xu, LX, Xie SP, Liu QY.  2013.  Fast and slow responses of the North Pacific mode water and Subtropical Countercurrent to global warming. Journal of Ocean University of China. 12:216-221.   10.1007/s11802-013-2189-6   AbstractWebsite

Six coupled general circulation models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are employed for examining the full evolution of the North Pacific mode water and Subtropical Countercurrent (STCC) under global warming over 400 years following the Representative Concentration Pathways (RCP) 4.5. The mode water and STCC first show a sharp weakening trend when the radiative forcing increases, but then reverse to a slow strengthening trend of smaller magnitude after the radiative forcing is stablized. As the radiative forcing increases during the 21st century, the ocean warming is surface-intensified and decreases with depth, strengthening the upper ocean's stratification and becoming unfavorable for the mode water formation. Moving southward in the subtropical gyre, the shrinking mode water decelerates the STCC to the south. After the radiative forcing is stabilized in the 2070s, the subsequent warming is greater at the subsurface than at the sea surface, destabilizing the upper ocean and becoming favorable for the mode water formation. As a result, the mode water and STCC recover gradually after the radiative forcing is stabilized.

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.