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

Abstract

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.

Interannual variability of winter precipitation linked to upper ocean heat content off the east coast of Korea

“…Here, PCA was applied to validate the HYCOM products with in situ and satellite observations. The results described in the next section are consistent with previous results from the PCA of sea surface height (SSH) anomaly (Choi et al, ) and the upper OHC anomaly in the same region with a slightly different H (set to 500 m) (Yoon et al, ), to extract interannual variations of upper OHC and SSH, relevant to the EKWC meandering.…”

“…More importantly, the second‐mode Q a shows dominant interannual variability with a spatial pattern ( q 2 ) exhibiting a distinct east–west contrast (Figures (c) and (e)). Such a clear contrast in q 2 between the eastern and western parts is consistent with results obtained by analysing temperature data observed in the upper 500 m for the last 30 years (Yoon et al, ). In particular, Yoon et al .…”

“…In particular, Yoon et al . () indicate that the heaving effects due to TWC and branching EKWC primarily control the upper OHC changes at decadal and interannual timescales. The upper OHC changes are also linked to intermediate water properties (Nam et al, ), e.g.…”

“…In the eastern ES, larger volume transport of TWC in autumn derives more precipitations in the ES side of Japanese archipelago in the following winter (Hirose et al, ). However, considering the distinct east–west contrast of the upper OHC, as demonstrated in the previous section and discussed previously (Yoon et al, ; Nam et al, ), it corresponds to a weaker or no EKWC (smaller volume transport of the EKWC) and a smaller upper OHC (lower SST) in the western ES. More precipitations with northeasterly SSW correspond to a smaller upper OHC (lower SST) and a weaker EKWC along the Korean east coast (e.g.…”

Causes of Interannual Variation of Summer Mean Alongshore Current Near the East Coast of Korea Derived From 16‐Year‐Long Observational Data

“…The NKCC development has been discussed as being related to buoyancy forcing (Park & Lim, 2017), wind stress curl (Kim & Yoon, 1996;Seung, 1992), and wind stress (Na et al, 2010) in the northwestern East Sea. The relationship between the two western boundary currents (WBCs) has been reported in both numerical (Seung & Kim, 1989) and observational studies (Lee & Niiler, 2010) impacts on interannual and decadal variations in intermediate water properties and zonally contrasting upper ocean heat content were recently highlighted Yoon et al, 2016).…”