Production and analysis of a Southern Ocean state estimate

Mazloff, Matthew R.

doi:10.1575/1912/1282

Cited by 4 publications

(3 citation statements)

References 67 publications

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“…The background (initial condition) temperature and salinity uncertainties are chosen to equal the climatological variability for each level and are shown in Figure 4 [ Mazloff , 2006; Forget and Wunsch , 2007]. This approach includes spatially varying noise and the representation error estimate of Gouretski and Koltermann [2004], plus an uncertainty for climate variations.…”

Section: Observations and Associated Uncertaintiesmentioning

confidence: 99%

Upper ocean state estimation in the Southern Ocean Gas Exchange Experiment region using the four-dimensional variational technique

Dwivedi¹,

Haine

Castillo³

2011

J. Geophys. Res.

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A prototypical ocean circulation model, and associated 4‐D variational data assimilation system, is configured in support of the Southern Ocean Gas Exchange Experiment (Southern Ocean GasEx). The regional circulation model has 4 km horizontal resolution and 5 m vertical resolution in the upper ocean. In situ temperature and salinity observations and remotely sensed, gridded sea surface temperature and sea surface height observations are combined with the circulation model between 6 March and 4 April 2008. The benefits of customized data assimilation in support of a single oceanographic cruise are illustrated using Southern Ocean GasEx as a case study. The assimilated fields fit the observations within their respective uncertainties and fit 4–6 times better than the initial guess solution before assimilation. The fit of the assimilated fields is up to 100 times closer to observations than various global state estimate products using a cost function variance metric. The space‐time variability in mixed layer depth is consistent with the Southern Ocean GasEx observations and shows a deepening through March 2008. This variability is correlated with sea level height anomalies, sea surface temperature, and air temperature, during the assimilation window. The mixed layer depth estimate between 21 March and 4 April 2008 at the location of the Southern Ocean GasEx deliberate tracer release is 41–54 ± 6 m. The average zonal volume flux estimate is 16 ± 1.9 Sv (1 Sv is 106 m3 s−1) for latitudes 50.7°S–51.8°S, longitude 38.5°W. The zonal volume flux approximately halves during 6–16 March; temporal changes in volume flux are associated with geostrophic circulation but not with the Ekman circulation.

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Section: Observations and Associated Uncertaintiesmentioning

confidence: 99%

Upper ocean state estimation in the Southern Ocean Gas Exchange Experiment region using the four-dimensional variational technique

Dwivedi¹,

Haine

Castillo³

2011

J. Geophys. Res.

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“…Some of its key strengths are that SOSE has a better spatial and temporal resolution than most state estimate models and is the highest-resolution model used in this study. It is dynamically consistent and best-fit to the available 190 observations, and its biases are well-documented (Mazloff and National Center for Atmospheric Research Staff, 2021).…”

Section: Southern Ocean State Estimatementioning

confidence: 81%

Water mass transformation variability in the Weddell Sea in ocean reanalyses

et al. 2023

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Abstract. This study investigates the variability of water mass transformation (WMT) within the Weddell Gyre (WG). The WG serves as a pivotal site for the Meridional Overturning Circulation (MOC) and ocean ventilation because it is the primary origin of the largest volume of water mass in the global ocean: Antarctic Bottom Water (AABW). Recent mooring data suggest substantial seasonal and interannual variability of AABW properties exiting the WG, and studies have linked the variability to the large-scale climate forcings affecting wind stress in the WG region. However, the specific thermodynamic mechanisms that link variability in surface forcings to variability in water mass transformations and AABW export remain unclear. This study explores how current state-of-the-art data-assimilating ocean reanalyses can help fill the gaps in our understanding of the thermodynamic drivers of AABW variability in the WG via WMT volume budgets derived from Walin's classic WMT framework. The three ocean reanalyses used are the following: Estimating the Circulation and Climate of the Ocean state estimate (ECCOv4), Southern Ocean State Estimate (SOSE) and Simple Ocean Data Assimilation (SODA). From the model outputs, we diagnose a closed form of the water mass budget for AABW that explicitly accounts for transport across the WG boundary, surface forcing, interior mixing and numerical mixing. We examine the annual mean climatology of the WMT budget terms, the seasonal climatology and finally the interannual variability. Our finding suggests that the relatively coarse resolution of these models did not realistically capture AABW formation, export and variability. In ECCO and SOSE, we see strong interannual variability in AABW volume budget. In SOSE, we find an accelerating loss of AABW during 2005–2010, driven largely by interior mixing and changes in surface salt fluxes. ECCO shows a similar trend during a 4-year time period starting in late 2007 but also reveals such trends to be part of interannual variability over a much longer time period. Overall, ECCO provides the most useful time series for understanding the processes and mechanisms that drive WMT and export variability in the WG. SODA, in contrast, displays unphysically large variability in AABW volume, which we attribute to its data assimilation scheme. We also examine correlations between the WMT budgets and large-scale climate indices, including El Niño–Southern Oscillation (ENSO) and Southern Annular Mode (SAM), and find no strong relationships.

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“…All computer code, Supporting Information S1, and some of the processed model fields used in this analysis are available in an open-access repository (Narayanan, 2021). The complete model fields are available through the Southern Ocean State Estimate website (R. M. Mazloff, 2017). by the MEOP, Argo, and SOCCOM consortia.…”

Section: Appendix A: Discretization Of the Rates Of Watermass Transfo...mentioning

confidence: 99%

Zonal Distribution of Circumpolar Deep Water Transformation Rates and Its Relation to Heat Content on Antarctic Shelves

et al. 2023

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Circumpolar Deep Water (CDW) is a relatively warm layer of water (∼1-2°C) that is part of the lower branch of the global overturning circulation (Talley, 2013). CDW upwells in the subpolar gyres of the Southern Ocean and mixes with surface waters, transforming into lighter watermasses (Pellichero et al., 2018). CDW can also shoal onto the Antarctic continental shelf where it may undergo mixing with shelf watermasses, transforming into heavier and cooler Dense Shelf Water (DSW with σ θ ≥ 27.86 kg/m 3 ; Orsi et al., 1999). In some regions of Antarctica, CDW does not undergo transformation as it flows onto the continental shelf, retaining its warmer offshore properties, thereby elevating the temperatures at the base of ice shelves along the coastline Ribeiro et al., 2021).Another prominent watermass that CDW can transform into, as it encounters coastal polynyas, is a cooler version of itself, called modified-CDW (mCDW; with 28 < γ n < 28.27 kg/m 3 ; Williams et al., 2016). Along the ice shelf edge, mCDW has been found even in regions with a cold-cavity ice shelf, such as the Weddell Sea (Årthun et al., 2012), Prydz Bay (Williams et al., 2016, and the Ross Sea (Piñones et al., 2019). Though mCDW is a cooler watermass, it still remains warmer than the near-freezing waters formed on the continental shelves; hence it has the ability to elevate the melt rates of ice shelves (Adusumilli et al., 2020). Throughout the rest of this text,

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Production and analysis of a Southern Ocean state estimate

Cited by 4 publications

References 67 publications

Upper ocean state estimation in the Southern Ocean Gas Exchange Experiment region using the four-dimensional variational technique

Upper ocean state estimation in the Southern Ocean Gas Exchange Experiment region using the four-dimensional variational technique

Water mass transformation variability in the Weddell Sea in ocean reanalyses

Zonal Distribution of Circumpolar Deep Water Transformation Rates and Its Relation to Heat Content on Antarctic Shelves

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