A Mechanistic Analysis of Tropical Pacific Dynamic Sea Level in
GFDL-OM4 under OMIP-I and OMIP-II Forcings

Hsu, Chia‐Wei; Yin, Jingxue; Griffies, Stephen M.; Dussin, Raphaël

doi:10.5194/gmd-2020-374

Cited by 3 publications

(3 citation statements)

References 32 publications

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“…However, we find minor biases in both reference configurations that are most likely due to the forcing. Hsu et al (2021) report a wind stress curl bias in JRA55-do in the Pacific between 4 and 9 • N that acts to diminish the meridional SSH gradient and flatten the SSH trough at this latitude. This is consistent with the warm bias we found at this latitudinal band.…”

Section: Discussionmentioning

confidence: 95%

Decadal sea-level variability in the Australasian Mediterranean Sea

Wagner

Böning

2021

Ocean Sci.

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Abstract. Strong regional sea-level trends, mainly related to basin-wide wind stress anomalies, have been observed in the western tropical Pacific over the last 3 decades. Analyses of regional sea level in the densely populated regions of the neighbouring Australasian Mediterranean Sea (AMS; also called tropical Asian seas) are hindered by its complex topography and respective studies are sparse. We used a series of global eddy-permitting ocean models, including a high-resolution configuration that resolves the AMS with 120∘ horizontal resolution, forced by a comprehensive atmospheric forcing product over 1958–2016 to characterize the patterns and magnitude of decadal sea-level variability in the AMS. The nature of this variability is elucidated further by sensitivity experiments with interannual variability restricted to either the momentum or buoyancy fluxes, building on an experiment employing a repeated-year forcing without interannual variability in all forcing components. Our results suggest that decadal fluctuations of the El Niño–Southern Oscillation (ENSO) account for over 80 % of the variability in all deep basins of the region, except for the central South China Sea (SCS). Changes related to the Pacific Decadal Oscillation (PDO) are most pronounced in the shallow Arafura and Timor seas and in the central SCS. On average, buoyancy fluxes account for less than 10 % of decadal SSH variability, but this ratio is highly variable over time and can reach values of up to 50 %. In particular, our results suggest that buoyancy flux forcing amplifies the dominant wind-stress-driven anomalies related to ENSO cycles. Intrinsic variability is mostly negligible except in the SCS, where it accounts for 25 % of the total decadal SSH variability.

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Section: Discussionmentioning

confidence: 95%

Decadal sea-level variability in the Australasian Mediterranean Sea

Wagner

Böning

2021

Ocean Sci.

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“…However, we find minor biases in both reference configurations that are most likely due to the forcing. Hsu et al (2021) reported a wind stress curl bias in JRA55-do in the Pacific between 4-9 • N that acts to diminish the meridional SSH gradient and flatten the SSH trough at this latitude. This is consistent with the warm bias we found at this latitudinal band.…”

Section: Discussionmentioning

confidence: 99%

Decadal sea level variability in the Australasian Mediterranean Sea

Wagner

Böning

2021

Preprint

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Abstract. Strong, regional sea level trends, mainly related to basin–wide wind stress anomalies, have been observed in the western tropical Pacific over the last three decades. Analyses of regional sea level in the densely populated regions of the neighbouring Australasian Mediterranean Sea (AMS) are hindered by its complex topography and respective studies are sparse. We used a series of global, eddy permitting ocean models, including a high–resolution configuration that resolves the AMS with horizontal resolution, forced by a comprehensive atmospheric forcing product over 1958–2016, to characterize the patterns and magnitude of decadal sea level variability in the AMS. The nature of this variability is elucidated further by sensitivity experiments with interannual variability restricted to either the momentum or buoyancy fluxes, building on an experiment employing a repeated-year forcing without interannual variability in all forcing components. Our results suggest that decadal fluctuations of ENSO account for over 80 % of the variability in all deep basins of the region, except for the central South China Sea (SCS). PDO–related changes are most pronounced in the shallow Arafura and Timor seas and in the central SCS. On average, buoyancy fluxes account for less than 10 % of decadal SSH variability, although this ratio is highly variable over time and can reach values of up to 50 %. In particular, our results suggest that buoyancy flux forcing amplifies the dominant wind stress driven anomalies related to ENSO cycles. Intrinsic variability is mostly negligible except in the SCS, where it accounts for 25 % of the total decadal SSH variability.

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“…There is a related problem with coupled oceanatmosphere models which fail to generate realistic El Niños (Guilyardi et al, 2009;Ham and Kug, 2012;Flato et al, 2013;Hsu et al, 2021). This again may be due to the resolution of the atmospheric component being insufficient to accurately represent features such as the ITCZ.…”

Section: El Niño Models and Theoriesmentioning

confidence: 99%

On the low western Pacific sea levels observed prior to strong East Pacific El Niños

Webb

2021

Ocean Sci.

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Abstract. Research, based on both observations and ocean models, has indicated that strong East Pacific El Niños are preceded by the development of unusually low sea levels at the western end of the North Equatorial Trough early in the year. This results in an increase in the strength of the North Equatorial Counter Current which, aided by low sea levels due to the annual Rossby wave, then transports West Pacific Warm Pool water to the central and eastern Pacific. Here, an ocean model is used to investigate the factors affecting sea level prior to the 1982–1983 East Pacific El Niño. The results indicate that during this period the reduction in sea level was caused by Ekman pumping, due to the local winds, acting over a period of many months. The north–south distances involved mean that such upwelling can be connected to the westerly wind phase of Madden–Julian Oscillations. Since the 1980s, the quality and quantity of global wind measurement has steadily improved. So, if the Ekman pumping hypothesis is correct, the better-quality wind data available prior to the 1997–1998 and 2015–2016 East Pacific El Niños should also show unusually large Ekman pumping in the same region, over a similar long period. This is tested and found to be correct. However, a study of the integrated Ekman pumping for the period 1976 to 2015 indicates that in some years similar events did not develop despite a comparable amount of pumping during the first part of the year. The results imply that significant Ekman pumping early in the year is a necessary but not sufficient requirement for the development of a strong East Pacific El Niño.

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A Mechanistic Analysis of Tropical Pacific Dynamic Sea Level in GFDL-OM4 under OMIP-I and OMIP-II Forcings

Cited by 3 publications

References 32 publications

Decadal sea-level variability in the Australasian Mediterranean Sea

Decadal sea-level variability in the Australasian Mediterranean Sea

Decadal sea level variability in the Australasian Mediterranean Sea

On the low western Pacific sea levels observed prior to strong East Pacific El Niños

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