The HYCOM (HYbrid Coordinate Ocean Model) data assimilative system

Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong Internal gravity waves are propagating disturbances of the ocean's density stratification. Their physics resembles that of surface gravity waves but with buoyancy rather than gravity providing their restoring force -making them much larger (10's to 100's of meters instead of 1 to 10 meters) and slower (hours instead of seconds). Generated primarily by tidal flow past seafloor topography and winds blowing on the sea surface, and typically having multi-kilometer-scale horizontal wavelengths, their estimated 1 TW of deep-sea dissipation is understood to play a crucial role in the ocean's global redistribution of heat and momentum 12 . A major challenge is to improve understanding of internal wave generation, propagation, steepening and dissipation, so that the role of internal waves can be more accurately incorporated in climate models.The internal waves that originate from the Luzon Strait on the eastern margin of the South China Sea (SCS) are the largest documented in the global oceans ( Figure 1).As the waves propagate west from the Luzon Strait they steepen dramatically ( Figure 1a), producing distinctive solitary wave fronts evident in sun glint and synthetic aperture radar (SAR) images from satellites ( Figure 1b). When they shoal onto the continental slope to the west, the downward displacement of the ocean's layers associated with these solitary waves can exceed 250 m in 5 minutes 8 . On such a scale, these waves pose hazards for underwater navigation and offshore drilling 4 , and supply nutrients from the deep ocean that nourish coral reefs 1 and pilot whale populations that forage in their wakes 13 .Over the past decade a number of field studies have been conducted in the region; this work has been comprehensively reviewed 10,11 . All of these studies, however, focused on the propagation of the internal waves across the SCS and their interactions with the continental shelf of China. Until the present study there had been no substantial in situ data gathered at the generation site of the Luzon Strait, in large part because of the extremely challenging operating conditions. A consequence has been persistent 5 confusion regarding the nature of the generation mechanism 11 ; an underlying cause being the sensitivity of the models employed to the system parameters, such as the chosen transect for a two-dimensional model, the linear internal wave speed or the assumed location of the waves' origin within the Luzon Strait. Furthermore, the lack of in situ data from the Luzon Strait has meant an inability to test numerical predictions of energy budgets 9 and no knowledge of the impact of the Kuroshio on the emergence of internal solitary waves 11 .The goal of IWISE is to obtain the first comprehensive in situ data set from the Luzon Strait, which in combination with high-resolution three-dimensional numerical modeling supports a cradle-to-grave picture ...

show abstract

“…The near-field model data (Figure 2a), with a horizontal resolution of 250m, were generated using a 154-layer implementation of the 41 .…”

Section: Numerical Modelsmentioning

confidence: 99%

The formation and fate of internal waves in the South China Sea

Alford

Peacock

MacKinnon

et al. 2015

Nature

503

329

View full text Add to dashboard Cite

show abstract

“…The settings are described in Chassignet et al (2007). This relaxation probably removes part of the interannual variability, but is unavoidable considering the uncertainties in freshwater fluxes.…”

Section: P Sakov Et Al: Topaz4 Systemmentioning

confidence: 99%

“…Running an EnKF for a large-scale, eddyresolving ocean model is therefore often prohibitively expensive. Perhaps as a direct result of this, most large-scale, eddy-resolving ocean forecast systems use a single deterministic forecast, together with either a variant of Ensemble Optimal Interpolation (EnOI; Oke et al, 2010), where the background error covariance is approximated by a time-invariant ensemble or a seasonally varying ensemble (Brasseur et al, 2005); or a statistical DA scheme, like Optimal Interpolation (OI; Chassignet et al, 2007, see Cummings et al, 2009, for a review). Srinivasan et al (2011) compare these methods in a twin experiment and show that they yield a similar performance.…”

Section: Introductionmentioning

confidence: 99%

TOPAZ4: an ocean-sea ice data assimilation system for the North Atlantic and Arctic

et al. 2012

View full text Add to dashboard Cite

Abstract. We present a detailed description of TOPAZ4, the latest version of TOPAZ -a coupled ocean-sea ice data assimilation system for the North Atlantic Ocean and Arctic. It is the only operational, large-scale ocean data assimilation system that uses the ensemble Kalman filter. This means that TOPAZ features a time-evolving, state-dependent estimate of the state error covariance. Based on results from the pilot MyOcean reanalysis for 2003-2008, we demonstrate that TOPAZ4 produces a realistic estimate of the ocean circulation in the North Atlantic and the sea-ice variability in the Arctic. We find that the ensemble spread for temperature and sea-level remains fairly constant throughout the reanalysis demonstrating that the data assimilation system is robust to ensemble collapse. Moreover, the ensemble spread for ice concentration is well correlated with the actual errors. This indicates that the ensemble statistics provide reliable state-dependent error estimates -a feature that is unique to ensemble-based data assimilation systems. We demonstrate that the quality of the reanalysis changes when different sea surface temperature products are assimilated, or when in-situ profiles below the ice in the Arctic Ocean are assimilated. We find that data assimilation improves the match to independent observations compared to a free model. Improvements are particularly noticeable for ice thickness, salinity in the Arctic, and temperature in the Fram Strait, but not for transport estimates or underwater temperature. At the same time, the pilot reanalysis has revealed several flaws in the system that have degraded its performance. Finally, we show that a simple bias estimation scheme can effectively detect the seasonal or constant bias in temperature and sea-level.

show abstract

“…Vertically, there are 36 terrain-following layers weighted to better resolve surface and bottom boundary layers. For open boundary conditions, the ocean model is one-way nested inside the 1/12°data assimilative North Atlantic Hybrid Coordinate Ocean Model [HYCOM/ NCODA (Chassignet et al 2007)]. At the model's open boundaries, free surface and depth-averaged velocity were specified using the external subtidal information defined by HYCOM/NCODA superimposed by eight tidal constituents (Q 1 , O 1 , P 1 , K 1 , N 2 , M 2 , S 2 , and K 2 ) derived from the OTIS regional tidal solution (Flather, 1976;Egbert & Erofeeva 2002).…”

Section: Model Setup Ocean Model (Roms)mentioning

confidence: 99%

“…Wavewatch III, 2.5°resolution (Tolman 2002)], and ocean (e.g. HYCOM, 1/12°equatorial resolution Chassignet et al 2007) forecast systems have been operating over the past 10 years. However, the horizontal resolution of some of these forecast systems (e.g.…”

Section: Introductionmentioning

confidence: 99%

An integrated ocean circulation, wave, atmosphere, and marine ecosystem prediction system for the South Atlantic Bight and Gulf of Mexico

Xue

Zambon

Yao

et al. 2015

Journal of Operational Oceanography

View full text Add to dashboard Cite

An integrated nowcast/forecast modelling system covering the South Atlantic Bight and Gulf of Mexico (SABGOM) is in operation, utilizing sophisticated model coupling and parallel computing techniques. This three-dimensional, highresolution, regional nowcast/forecast system provides a nowcast and an 84 h forecast of marine weather, ocean waves and circulation, and basic marine ecosystem conditions to the public via a Google Map interface. The SABGOM system runs automatically daily and supports a series of user-defined online applications. Extensive model validations were performed online against in situ and satellite-observed ocean conditions. The SABGOM system exhibits a reliable capability of providing valuable forecasts.

show abstract

The HYCOM (HYbrid Coordinate Ocean Model) data assimilative system

Cited by 816 publications

References 57 publications

The formation and fate of internal waves in the South China Sea

The formation and fate of internal waves in the South China Sea

TOPAZ4: an ocean-sea ice data assimilation system for the North Atlantic and Arctic

An integrated ocean circulation, wave, atmosphere, and marine ecosystem prediction system for the South Atlantic Bight and Gulf of Mexico

Contact Info

Product

Resources

About