An Nguyen

An Nguyen
University of Texas at Austin | UT · Institute for Computational Engineering and Sciences

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44
Publications
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Introduction
Skills and Expertise

Publications

Publications (44)
Article
Full-text available
The upper ocean salinity in the eastern subpolar North Atlantic undergoes decadal fluctuations. A large fresh anomaly event occurred during 2012–2016. Using the ECCOv4r4 state estimate, we diagnose and compare mechanisms of this low salinity event with those of the 1990s fresh anomaly event. To avoid issues related to the choice of reference salini...
Preprint
The eastern subpolar North Atlantic upper ocean salinity undergoes decadal fluctuations. A large fresh anomaly event occurred during 2012–2016. Using the ECCO state estimate, we diagnose and compare mechanisms of this low salinity event with that of the 1990s fresh anomaly event. To avoid erroneous interpretations of physical mechanisms due to refe...
Article
Full-text available
Use of an ocean parameter and state estimation framework – such as the Estimating the Circulation and Climate of the Ocean (ECCO) framework – could provide an opportunity to learn about the spatial distribution of the diapycnal diffusivity parameter (κρ) that observations alone cannot due to gaps in coverage. However, we show that the inclusion of...
Preprint
Full-text available
Use of an ocean parameter and state estimation framework–such as the Estimating the Circulation & Climate of the Ocean (ECCO) framework–could provide an opportunity to learn about the spatial distribution of the diapycnal diffusivity parameter (κρ) that observations alone cannot due to gaps in coverage. However, we show that the assimilation of exi...
Article
Full-text available
The Antarctic coastal ocean impacts sea level rise, deep-ocean circulation, marine ecosystems, and the global carbon cycle. To better describe and understand these processes and their variability, it is necessary to combine the sparse available observations with the best-possible numerical descriptions of ocean circulation. In particular, high ice...
Article
Full-text available
A description and assessment of the first release of the Arctic Subpolar gyre sTate Estimate (ASTE_R1), a data‐constrained ocean‐sea ice model‐data synthesis, is presented. ASTE_R1 has a nominal resolution of 1/3° and spans the period 2002–2017. The fit of the model to an extensive (O(10⁹)) set of satellite and in situ observations was achieved thr...
Preprint
Full-text available
The Antarctic coastal ocean is impacting sea level rise, deep-ocean circulation, marine ecosystems, and global carbon cycle. To better describe and understand these processes and their variability, it is necessary to combine the sparse available observations with best-possible numerical descriptions of ocean circulation. In particular, high ice-she...
Article
Full-text available
A regional data‐constrained coupled ocean‐sea ice general circulation model and its adjoint are used to investigate mechanisms controlling the volume transport variability through Bering Strait during 2002 to 2013. Comprehensive time‐resolved sensitivity maps of Bering Strait transport to atmospheric forcing can be accurately computed with the adjo...
Article
The lack of continuous spatial and temporal sampling of hydrographic measurements in large parts of the Arctic Ocean remains a major obstacle for quantifying mean state and variability of the Arctic Ocean circulation. This shortcoming motivates an assessment of the utility of Argo-type floats, the challenges of deploying such floats due to the pres...
Article
Full-text available
In 1999, the consortium on Estimating the Circulation and Climate of the Ocean (ECCO) set out to synthesize the hydrographic data collected by the World Ocean Circulation Experiment (WOCE) and the satellite sea surface height measurements into a complete and coherent description of the ocean, afforded by an ocean general circulation model. Twenty y...
Article
Full-text available
A realistic representation of sea-ice deformation in models is important for accurate simulation of the sea-ice mass balance. Simulated sea-ice deformation from numerical simulations with 4.5, 9, and 18 km horizontal grid spacing and a viscous–plastic (VP) sea-ice rheology are compared with synthetic aperture radar (SAR) satellite observations (RGP...
Article
Full-text available
In ice-covered regions it is challenging to determine constituent budgets – for heat and momentum, but also for biologically and climatically active gases like carbon dioxide and methane. The harsh environment and relative data scarcity make it difficult to characterize even the physical properties of the ocean surface. Here, we sought to evaluate...
Poster
Full-text available
The Arctic Observing Open Science Meeting (AOOSM) held in Seattle, Washington during 17-19 November 2015 provided an opportunity for the Arctic science community to present and discuss findings and advances in Arctic observing. A diverse agenda of plenary presentations, parallel sessions with extended discussion, and a poster session provided a for...
Article
Full-text available
A realistic representation of sea ice deformation in models is important for accurate simulation of the sea ice mass balance. In this study, model ice strength sensitivity experiments show an increase in Arctic Basin sea ice volume of 7 % and 35 % for a decrease in ice strength of, respectively, 30 % and 70 %, after 8 years of model integration. Th...
Article
Full-text available
In ice-covered regions it can be challenging to determine air-sea exchange – for heat and momentum, but also for gases like carbon dioxide and methane. The harsh environment and relative data scarcity make it difficult to characterize even the physical properties of the ocean surface. Here, we seek a mechanistic interpretation for the rate of air-s...
Article
Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings heat, fresh water and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper pathways of PW are investigated using simulations with six state-of-the art regional a...
Chapter
Bering Strait is the only ocean connection between the Pacific and the Arctic. The flow through this narrow and shallow strait links the Pacific and Arctic oceans and impacts oceanic conditions downstream in the Chukchi Sea and the Western Arctic. We present a model synthesis of exchanges through Bering Strait at monthly to decadal time scales, inc...
Article
Full-text available
1] The Arctic freshwater (FW) has been the focus of many modeling studies, due to the potential impact of Arctic FW on the deep water formation in the North Atlantic. A comparison of the hindcasts from ten ocean-sea ice models shows that the simulation of the Arctic FW budget is quite different in the investigated models. While they agree on the ge...
Article
A coupled ocean and sea ice model is used to investigate dense water (DW) formation in the Chukchi and Bering shelves and the pathways by which this water feeds the upper halocline. Two 1992-2008 data-constrained solutions at 9- and 4-km horizontal grid spacing show that 1) winter sea ice growth results in brine rejection and DW formation; 2) the D...
Article
Full-text available
Six Arctic Ocean Model Intercomparison Project model simulations are compared with estimates of sea ice thickness derived from pan-Arctic satellite freeboard measurements (2004-2008); airborne electromagnetic measurements (2001-2009); ice draft data from moored instruments in Fram Strait, the Greenland Sea, and the Beaufort Sea (1992-2008) and from...
Article
Full-text available
From a collection at 18,588 current meter locations spanning 12,825 observation years, we examine ocean circulation in terms of topostrophy. We affirm previous indications of strongly positive topostrophy toward higher latitudes, and we consider variation with depth. We explore use of the current meter data set for evaluating models skills. This is...
Article
Full-text available
We present an optimized 1992–2008 coupled ice-ocean simulation of the Arctic Ocean. A Green's function approach adjusts a set of parameters for best model-data agreement. Overall, model-data differences are reduced by 45%. The optimized simulation reproduces the negative trends in ice extent in the satellite records. Volume and thickness distributi...
Article
Sea ice movement is driven by surface wind and ocean currents. The spatial inhomogeneity of these forces causes internal sea ice stress gradients, which eventually cause ice to ridge or break up. This sea ice deformation is an important process for (1) the sea ice mass balance, (2) brine rejection into the ocean, (3) regulation of ocean-to-air heat...
Article
We examine volumetric census in temperature-salinity (TS) as a way of measuring and analyzing the fidelity of Arctic Ocean models. We separate the Arctic Ocean and adjacent seas into 8 precisely defined domains. We examine output from three models: global and regional configurations of the MITgcm/ECCO2 at the Jet Propulsion Laboratory and the NEMO/...
Article
The Arctic sea ice in many respects is an important component of the Earth's climate system, e.g., sea ice governs the ocean to atmosphere heat flux, freezing and melting influences the upper ocean salinity and density, and sea ice dynamics act as a latent energy transport. During recent years substantial changes of the Arctic sea ice cover have be...
Article
Full-text available
The halocline in the Arctic Ocean plays an important role in regulating heat exchange at the bottom of the mixed layer and it has a direct effect on the ocean sea ice energy balance and sea ice mass balance. Modeling the halocline, however, remains a challenge in current state-of-the-art coupled ocean sea ice models including those that participate...
Article
Full-text available
The Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project aims to produce a best- possible, time-evolving synthesis of most available ocean and sea-ice data at a resolution that permits ocean eddies. ECCO2 analyses are obtained via least squares fit of a global, full-depth-ocean, and sea-ice configuration of the Massachusett...
Article
Full-text available
One of the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project's objectives is to realistically estimate the Arctic Ocean circulation and sea-ice distribution during the ocean satellite era (1978-present). Towards the release of a global optimized ECCO2 solution to the scientific community, an optimized Arctic solution has...
Article
Full-text available
One of the primary objectives of the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project is to realistically estimate the Arctic ocean circulation and sea ice distribution during the ocean satellite era (1978-present). The ECCO2 solution is obtained by fitting a high-resolution (18-km horizontal grid spacing) global-ocean...
Article
Full-text available
We aim to demonstrate the feasibility and utility of global, eddying ocean and sea ice state estimation. A first synthesis for the period 1992-2002 has been obtained using a Green's functions approach. Data constraints include hydrography, altimetry, gravity, drifter, and observations of sea-ice. Although the control space is small (~80 parameters)...

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