The processes of surface warming hiatus in the East/Japan Sea

Despite ongoing increases in anthropogenic greenhouse-gas emission, an increasing rate of global surface temperature has remained steadily from 1997 to 2012, which has been referred as the ‘global warming hiatus’. While the global surface temperature tended to decrease during the hiatus period, the increasing heat contents of the ocean deep layer were observed. Therefore, this time period is defined when the thermal energy is redistributed to the ocean interior. However, the impact of this ‘global warming hiatus’ depends on regions and transferring mechanism of energy from the atmosphere to the ocean interior is unclear on a regional scale yet. In this study, we investigated how the global warming hiatus affected the marginal sea such as East/Japan Sea (EJS). More importantly, we examined the potential mechanism for warming hiatus. The EJS is the semi-enclosed marginal sea of 2500 meters depth and has characteristics having various physical phenomena. Specifically, we analyzed regional temperature trends of non-hiatus and hiatus periods to investigate physical processes that cause warming hiatus in the EJS. In order to do that, the ECMWF reanalysis data (ORAS4) was used to examine temperature changes in each depth. Furthermore, Ensemble Empirical Mode Decomposition (EEMD) method was applied to ocean temperature reanalysis data for understanding temperature changes in different time scales. Through this research, we found that in sea surface temperature variability, there is a slowdown of warming rate (-0.05℃/decade) in upper layer and increase of warming rate (0.03℃/decade) in deeper layer from 2000 to 2013. In addition, we compared the surface temperature variation with the intensity of other mesoscale phenomena such as eddy, wind stress that can cause heat transfer to deeper layer. While previous studies have reported the effects of warming hiatus on large scale, this study aims to analyze the cause of hiatus on regional scale.