Different Influences of Mesoscale Oceanic Eddies on the North Pacific Subsurface Low Potential Vorticity Water Mass Between Winter and Summer.

The generation and dissipation of North Pacific subsurface low potential vorticity water mass (SLPVW) affect various ocean‐atmosphere dynamic and thermodynamic processes on a wide range of time scales. Mesoscale oceanic eddies are believed to play an important role in the variation of SLPVW. National Centers for Environmental Prediction (NCEP)/NCEP‐Climate Forecast System Reanalysis coupled data set during 1979–2010 has been analyzed to investigate the different influences of mesoscale oceanic eddies on the SLPVW between winter and summer. It is found that the correlation between the sea surface height and SLPVW volume in winter is positive on the north of 30°N but negative on the south of 30°N, which is mainly caused by the eddy vorticity strength. The negative correlation value region has more strong anticyclones than the positive correlation value region, so the mixed layer depth in the negative (positive) correlation value region tends to be deeper (shallower) caused by stronger (weaker) anticyclones, which leads to the decreasing (increasing) of the low PV water mass under mixed layer depth (namely, SLPVW). Eddies also have obvious impacts on the subduction rate. The climatological eddy subduction rate can reach to 1.88 Sv in the NCEP‐Climate Forecast System Reanalysis, which accounts for 36.4% of the total subduction rate. In summer, the correlation between the sea surface height and SLPVW volume is remarkably negative. It is found that water diverges (converges) in the composite anticyclone (cyclone), which leads to the increasing (decreasing) of PV value in the composite anticyclone (cyclone), finally accelerates (hinders) the dissipation of SLPVW. Plain Language Summary: The study researched different influences of mesoscale oceanic eddies on the North Pacific subsurface low potential vorticity water mass (SLPVW) between winter and summer. The results revealed that eddies influence the formation of low potential vorticity water by changing turbulent heat flux in winter. Moreover, it is found that the relationship between oceanic eddies and SLPVW volume is influenced by the eddy vorticity strength. The mixed layer depth in the stronger (weaker) anticyclones tends to be deeper (shallower), which leads to the increasing (decreasing) of the low PV water mass but decreasing (increasing) of the low PV water mass under mixed layer depth (namely, SLPVW). The subduction rate varies greatly from year to year, suggesting the role of the interannual variation of eddies. In summer, the rotation of the eddies leads to the convergence and divergence, thus changing the stratification of the ocean and ultimately affecting the dissipation of SLPVW. The results might give the new insight to studies the role of mesoscale eddies on SLPVW, which have important implications for North Pacific climate scientists and predictions. Key Points: The relationship between oceanic eddies and SLPVW volume in winter is influenced by the eddy vorticity strengthThe subduction rate varies greatly from year to year, suggesting the role of the interannual variation of eddiesIn summer, water converges in the composite cyclone, which is beneficial to the retention of the SLPVW [ABSTRACT FROM AUTHOR]