Hanna Na

An east-west contrast of upper ocean heat content variation south of the subpolar front in the East/Japan Sea

Long-term variability of nonseasonal ocean heat content (OHC) in the upper 500 m in the East/Japan Sea (EJS) exhibits a distinct east-west contrast during the recent 30 years. The contrasting OHC variations are revisited and investigated more in detail by analyzing two observational data sets, the gridded data from 1976 to 2007 and in situ data from 1976 to 2011 in the southwestern EJS that covers the zone of western boundary current. The OHC variability shows in-phase and predominant decadal variation in both east and west regions before 1995, but uncorrelated and predominant interannual variations after 1995. Heaving effects due to major branches of warm currents in the EJS, the East Korea Warm Current (EKWC) in the western part and other two branches in the eastern part, mainly contribute to the OHC variations. The heaving effect in the western EJS is shown to be associated with changes in winter wind-stress curl field in the northern EJS. Weakening of the subpolar gyre due to weakening of positive wind-stress curl in the Japan Basin related with wintertime Western Pacific teleconnection pattern and Siberian High appears to enhance the northward penetration of the EKWC resulting in an increase of OHC in the western EJS. The heaving effect in the eastern EJS is significantly correlated with the Siberian High, but the causative mechanism is inconclusive. This study also demonstrates the importance of using highly resolved data sets for areas affected by strong and narrow boundary currents in computing and understanding the OHC variability.

Bottom pressure variability in the Kuroshio Extension driven by the atmosphere and ocean instabilities

The relative importance of atmospheric forcing on oceanic intraseasonal (7–60 days) barotropic variability is investigated in the Kuroshio Extension region by comparing in situ measurements with two models: a wind-forced barotropic model and an ocean general circulation model. Large-scale wind stress curl forcing (an atmospheric mode) becomes successively more influential with decreasing periods (at 7–15 day band, compared to 15–30 day and 30–60 day bands). On the other hand, oceanic instabilities (an oceanic mode) become more important with increasing period (at 30–60 day band, compared to 15–30 day and 7–15 day bands). Comparison between the barotropic model and the ocean general circulation model results reveals differences on the broader gyre scale: the atmospheric mode exhibits basin-mode-like spatial patterns with faster phase propagation from east to west, whereas the oceanic mode shows eddy-like spatial patterns with slower westward propagation. The atmospheric mode, which has received less attention on the intraseasonal time scale, contributes an important fraction to the barotropic variability in the Kuroshio Extension region.

Interannual to Decadal Variability of the Upper-Ocean Heat Content in the Western North Pacific and Its Relationship to Oceanic and Atmospheric Variability

AbstractThree-dimensional oceanic thermal structures and variability in the western North Pacific (NP) are examined on the interannual to decadal time scales and their relationship to oceanic and a...