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  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 35 (2010): 134-145, doi:10.1016/j.ocemod.2010.06.006.
    Description: As part of an effort to build an integrated observation and modeling system for the New York Bight, this study explores observing system design using a representer-based method. The Representer of a single observation describes the covariance between the observed quantity and ocean state at all locations at any time. It is related closely to the influence of the observation on control variable correction in a 4D Variational data assimilation system. We prove that these properties hold for the combination of representers that is associated with an arithmetic function of model variables or a group of observations. The representer-based method is used here to identify which of a set of proposed tracks for an autonomous coastal glider is better for predicting horizontal salt flux within the Hudson Shelf Valley in a 2-day forecast period. Twin experiments confirm the result. The system is also used to compare different observation strategies. We show that a glider that traverses a regular transect influences a larger area than a continuously profiling mooring, but the mooring carries stronger influence at the observation location. The representer analysis shows how the information provided by observations extends toward the dynamically upstream and how increasing the duration of the analysis window captures more dynamical connections and expands the area of influence of the observations in data assimilation. Overall, the study demonstrates that the representer methodology can quantitatively contrast different observational strategies and determine spatial patterns and temporal extent of the influence of observations, both of which are helpful for evaluating the design of observation networks.
    Description: This work was funded by National Science Foundation grant OCE-0238957.
    Keywords: Representer ; Adjoint ; Observing system design ; Adaptive sampling ; Observation influence ; New York Bight
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 2
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 4324–4339, doi:10.1002/2014JC010547.
    Description: In the coastal ocean off the Northeast U.S., the sea surface temperature (SST) in the first half of 2012 was the highest on the record for the past roughly 150 years of recorded observations. The underlying dynamical processes responsible for this extreme event are examined using a numerical model, and the relative contributions of air-sea heat flux versus lateral ocean advective heat flux are quantified. The model accurately reproduces the observed vertical structure and the spatiotemporal characteristics of the thermohaline condition of the Gulf of Maine and the Middle Atlantic Bight waters during the anomalous warming period. Analysis of the model results show that the warming event was primarily driven by the anomalous air-sea heat flux, while the smaller contribution by the ocean advection worked against this flux by acting to cool the shelf. The anomalous air-sea heat flux exhibited a shelf-wide coherence, consistent with the shelf-wide warming pattern, while the ocean advective heat flux was dominated by localized, relatively smaller-scale processes. The anomalous cooling due to advection primarily resulted from the along-shelf heat flux divergence in the Gulf of Maine, while in the Middle Atlantic Bight the advective contribution from the along-shelf and cross-shelf heat flux divergences was comparable. The modeling results confirm the conclusion of the recent analysis of in situ data by Chen et al. (2014a) that the changes in the large-scale atmospheric circulation in the winter of 2011–2012 primarily caused the extreme warm anomaly in the spring of 2012. The effect of along-shelf or cross-shelf ocean advection on the warm anomalies from either the Scotian Shelf or adjacent continental slope was secondary.
    Description: K.C. was supported by the Woods Hole Oceanographic Institution Postdoctoral Scholar program, the Coastal Ocean Institute, and the National Science Foundation (NSF) under grant OCE-1435602. G.G.G. was supported by NSF grants OCE-1435602 and OCE-1129125. Y.-O.K. was supported by the NSF grant OCE-1435602. W.G.Z. was supported by the NSF grant OCE-1129125.
    Description: 2015-12-15
    Keywords: Extreme temperature ; Heat budget ; Northeast U.S. coastal ocean ; Numerical modeling ; Air-sea interaction ; Climate change
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 35 (2010): 119-133, doi:10.1016/j.ocemod.2010.08.003.
    Description: Four-dimensional Variational data assimilation (4DVAR) in the Regional Ocean Modeling System (ROMS) is used to produce a best-estimate analysis of ocean circulation in the New York Bight during spring 2006 by assimilating observations collected by a variety of instruments during an intensive field program. An incremental approach is applied in an overlapped cycling system with 3-day data assimilation window to adjust model initial conditions. The model-observation mismatch for all observed variables is reduced substantially. Comparisons between model forecast and independent observations show improved forecast skill for about 15 days for temperature and salinity, and 2 to 3 days for velocity. Tests assimilating only certain subsets of the data indicate that assimilating satellite sea surface temperature improves the forecast of surface and subsurface temperature but worsens the salinity forecast. Assimilating in situ temperature and salinity from gliders improves the salinity forecast but has little effect on temperature. Assimilating HF-radar surface current data improves the velocity forecast by 1-2 days yet worsens the forecast of subsurface temperature. During some time periods the convergence for velocity is poor as a result of the data assimilation system being unable to reduce errors in the applied winds because surface forcing is not among the control variables. This study demonstrates the capability of 4DVAR data assimilation system to reduce model-observation mismatch and improve forecasts in the coastal ocean, and highlights the value of accurate meteorological forcing.
    Description: This work was funded by National Science Foundation grant OCE-0238957.
    Keywords: Data assimilation ; 4DVAR ; ROMS ; Ocean prediction ; New York Bight ; River plume
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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