Wind-versus eddy-forced regional sea level trends and variability in the North Pacific ocean

Bo Qiu, Shuiming Chen, Lixin Wu, Shinichiro Kida

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Abstract

Regional sea level trend and variability in the Pacific Ocean have often been considered to be induced by low-frequency surface wind changes. This study demonstrates that significant sea level trend and variability can also be generated by eddy momentum flux forcing due to time-varying instability of the background oceanic circulation. Compared to the broad gyre-scale wind-forced variability, the eddy-forced sea level changes tend to have subgyre scales and, in the North Pacific Ocean, they are largely confined to the Kuroshio Extension region (30�-40�N, 140�-175�E) and the Subtropical Countercurrent (STCC) region (18�-28�N, 130�-175�E). Using a two-layer primitive equation model driven by the ECMWF wind stress data and the eddy momentum fluxes specified by the AVISO sea surface height anomaly data, the relative importance of the wind- and eddy-forced regional sea level trends in the past two decades is quantified. It is found that the increasing (decreasing) trend south (north) of the Kuroshio Extension is due to strengthening of the regional eddy forcing over the past two decades. On the other hand, the decreasing (increasing) sea level trend south (north) of the STCC is caused by the decadal weakening of the regional eddy momentum flux forcing. These decadal eddy momentum flux changes are caused by the background Kuroshio Extension and STCC changes in connection with the Pacific decadal oscillation (PDO) wind pattern shifting from a positive to a negative phase over the past two decades.

LanguageEnglish
Pages1561-1577
Number of pages17
JournalJournal of Climate
Volume28
Issue number4
DOIs
StatePublished - Jan 1 2015

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eddy
sea level
countercurrent
momentum
oceanic circulation
Pacific Decadal Oscillation
sea surface height
gyre
trend
North Pacific Ocean
wind stress
surface wind
sea level change
anomaly
ocean

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

Wind-versus eddy-forced regional sea level trends and variability in the North Pacific ocean. / Qiu, Bo; Chen, Shuiming; Wu, Lixin; Kida, Shinichiro.

In: Journal of Climate, Vol. 28, No. 4, 01.01.2015, p. 1561-1577.

Research output: Contribution to journalArticle

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abstract = "Regional sea level trend and variability in the Pacific Ocean have often been considered to be induced by low-frequency surface wind changes. This study demonstrates that significant sea level trend and variability can also be generated by eddy momentum flux forcing due to time-varying instability of the background oceanic circulation. Compared to the broad gyre-scale wind-forced variability, the eddy-forced sea level changes tend to have subgyre scales and, in the North Pacific Ocean, they are largely confined to the Kuroshio Extension region (30\{"i}¿½-40\{"i}¿½N, 140\{"i}¿½-175\{"i}¿½E) and the Subtropical Countercurrent (STCC) region (18\{"i}¿½-28\{"i}¿½N, 130\{"i}¿½-175\{"i}¿½E). Using a two-layer primitive equation model driven by the ECMWF wind stress data and the eddy momentum fluxes specified by the AVISO sea surface height anomaly data, the relative importance of the wind- and eddy-forced regional sea level trends in the past two decades is quantified. It is found that the increasing (decreasing) trend south (north) of the Kuroshio Extension is due to strengthening of the regional eddy forcing over the past two decades. On the other hand, the decreasing (increasing) sea level trend south (north) of the STCC is caused by the decadal weakening of the regional eddy momentum flux forcing. These decadal eddy momentum flux changes are caused by the background Kuroshio Extension and STCC changes in connection with the Pacific decadal oscillation (PDO) wind pattern shifting from a positive to a negative phase over the past two decades.",
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