Differences of the Interdecadal Trend Shifts of Latent Heat Fluxes in Kuroshio and Gulf Stream Regions in the Warming Hiatus Background and the Possible Mechanisms

The authors researched the interdecadal trend shifts of latent heat flux (LHF) over the Kuroshio Extension (KE) and Gulf Stream (GS) regions during the warming and warming hiatus periods using the LHF data and relevant variables obtained from the Objectively Analyzed Air–Sea Fluxes Project of the Woods Hole Oceanographic Institution and the Ishii subsurface temperature and salinity data obtained from the Japan Agency for Marine–Earth Science and Technology. The small perturbation method, empirical orthogonal function analysis, and International Thermodynamic Equation of Seawater—2010 are applied in this research. Contrasting interdecadal trend shifts of LHF exist in the KE and GS regions. The interdecadal LHF trend of the KE region shifts from positive to negative around 2001, whereas that of the GS region shifts from negative to positive around 1993. The variation of the KE region primarily resulted from sea surface temperature change (ocean-induced), whereas that of the GS region resulted from wind speed (1979–1992; atmosphere-induced) and sea surface temperature (1993–2013). The interdecadal variations of ocean heat content (OHC) in the KE and GS regions are also different: The interdecadal variation of surface heat content in the KE region is consistent with the mixed layer, whereas that in the GS region is different from that in the deep layer. Meanwhile, the changes below the surface layer are more consistent. The internal heat content changes in both regions reflect the warming hiatus phenomenon. The internal heat content in the KE region influences first the lower layer and then the upper layer, whereas that in the GS region influences first the upper layer and then the lower layer. The difference between the surfaces of the KE and GS regions can be attributed to the difference between ocean and atmospheric factors. Moreover, the vertical difference of the interdecadal variation of internal heat content can be attributed to the structural difference between the two regions. All of these variations are associated with the warming hiatus and may affect the warming hiatus conversely.