On the nudging terms at open boundaries in regional ocean models

Chen, Xinping; Liu, Chuanyu; O’Driscoll, Kieran; Mayer, Bernhard; Su, Jian; Pohlmann, Thomas

doi:10.1016/j.ocemod.2013.02.006

Cited by 17 publications

(16 citation statements)

References 36 publications

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“…A detailed description of HAMSOM is provided by Pohlmann (1991Pohlmann ( , 1996Pohlmann ( , 2006. HAMSOM applications can be found, e.g., in Backhaus and Hainbucher (1987), Chen et al (2013), Pohlmann (1996), and Mathis and Pohlmann (2014). The 3D fields of temperature (T), salinity (S), advective flow and vertical turbulent mixing coefficients calculated by HAMSOM are used as forcing for ECOHAM.…”

Section: The Hamsom-ecoham Modelmentioning

confidence: 99%

“…Both, HAMSOM and ECOHAM, are applied to the same model domain and grid, comprising the entire North Sea, large parts of the northwest European continental shelf and parts of the adjacent Northeast Atlantic Ocean (see HAMSOM uses monthly, climatological distributions of T and S based on the World Ocean Atlas 2001 (Conkright et al, 2002) for initialization and open boundaries. The open boundary treatment for advective flow as well as T and S is described in Chen et al (2013). The meteorological forcing is derived from NCEP/NCAR reanalysis data (Kalnay et al, 1996;Kistler et al, 2001) and provides 6-hourly information on air temperature, cloud coverage, relative humidity and wind velocity components.…”

Section: Model Setupmentioning

confidence: 99%

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A Novel Modeling Approach to Quantify the Influence of Nitrogen Inputs on the Oxygen Dynamics of the North Sea

et al. 2017

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Oxygen (O 2 ) deficiency, i.e., dissolved O 2 concentrations below 6 mg O 2 L −1 , is a common feature in the southern North Sea. Its evolution is governed mainly by the presence of seasonal stratification and production of organic matter, which is subsequently degraded under O 2 consumption. The latter is strongly influenced by riverine nutrient loads, i.e., nitrogen (N) and phosphorus (P). As riverine P loads have been reduced significantly over the past decades, this study aims for the quantification of the influence of riverine and non-riverine N inputs on the O 2 dynamics in the southern North Sea. For this purpose, we present an approach to expand a nutrient-tagging technique for physical-biogeochemical models -often referred to as 'trans-boundary nutrient transports' (TBNT) -by introducing a direct link to the O 2 dynamics. We apply the expanded TBNT to the physical-biogeochemical model system HAMSOM-ECOHAM and focus our analysis on N-related O 2 consumption in the southern North Sea during 2000-2014. The analysis reveals that near-bottom O 2 consumption in the southern North Sea is strongly influenced by the N supply from the North Atlantic across the northern shelf edge. However, riverine N sources -especially the Dutch, German and British rivers -as well as the atmosphere also play an important role. In the region with lowest simulated O 2 concentrations (around 56 • N, 6.5 • E), riverine N on average contributes 39% to overall near-bottom O 2 consumption during seasonal stratification. Here, the German and the large Dutch rivers constitute the highest riverine contributions (11% and 10%, respectively). At a site in the Oyster Grounds (around 54.5 • N, 4 • E), the average riverine contribution adds up to 41%, even exceeding that of the North Atlantic. Here, highest riverine contributions can be attributed to the Dutch and British rivers adding up to almost 28% on average. The atmospheric contribution results in 13%. Our results emphasize the importance of anthropogenic N inputs and seasonal stratification for the O 2 conditions in the southern North Sea. They further suggest that reductions in the riverine and atmospheric N inputs may have a relevant positive effect on the O 2 levels in this region.

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Section: The Hamsom-ecoham Modelmentioning

confidence: 99%

Section: Model Setupmentioning

confidence: 99%

A Novel Modeling Approach to Quantify the Influence of Nitrogen Inputs on the Oxygen Dynamics of the North Sea

et al. 2017

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“…For tracers (T and S) radiation and radiative-nudging OBCs were used in the case of inflow and outflow, respectively. A detailed description of the OBCs is provided by Chen et al (2013). The HAMSOM simulation was carried out with a 10 min time step.…”

Section: Model Setup and Forcing Datamentioning

confidence: 99%

Looking beyond stratification: a model-based analysis of the biological drivers of oxygen deficiency in the North Sea

et al. 2016

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Abstract. Low oxygen conditions, often referred to as oxygen deficiency, occur regularly in the North Sea, a temperate European shelf sea. Stratification represents a major process regulating the seasonal dynamics of bottom oxygen, yet, lowest oxygen conditions in the North Sea do not occur in the regions of strongest stratification. This suggests that stratification is an important prerequisite for oxygen deficiency, but that the complex interaction between hydrodynamics and the biological processes drives its evolution.In this study we use the ecosystem model HAMSOM-ECOHAM to provide a general characterisation of the different zones of the North Sea with respect to oxygen, and to quantify the impact of the different physical and biological factors driving the oxygen dynamics inside the entire subthermocline volume and directly above the bottom.With respect to oxygen dynamics, the North Sea can be subdivided into three different zones: (1) a highly productive, non-stratified coastal zone, (2) a productive, seasonally stratified zone with a small sub-thermocline volume, and (3) a productive, seasonally stratified zone with a large subthermocline volume. Type 2 reveals the highest susceptibility to oxygen deficiency due to sufficiently long stratification periods ( > 60 days) accompanied by high surface productivity resulting in high biological consumption, and a small subthermocline volume implying both a small initial oxygen inventory and a strong influence of the biological consumption on the oxygen concentration.Year-to-year variations in the oxygen conditions are caused by variations in primary production, while spatial differences can be attributed to differences in stratification and water depth. The large sub-thermocline volume dominates the oxygen dynamics in the northern central and northern North Sea and makes this region insusceptible to oxygen deficiency. In the southern North Sea the strong tidal mixing inhibits the development of seasonal stratification which protects this area from the evolution of low oxygen conditions. In contrast, the southern central North Sea is highly susceptible to low oxygen conditions (type 2).We furthermore show that benthic diagenetic processes represent the main oxygen consumers in the bottom layer, consistently accounting for more than 50 % of the overall consumption. Thus, primary production followed by remineralisation of organic matter under stratified conditions constitutes the main driver for the evolution of oxygen deficiency in the southern central North Sea. By providing these valuable insights, we show that ecosystem models can be a useful tool for the interpretation of observations and the estimation of the impact of anthropogenic drivers on the North Sea oxygen conditions.

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“…. In general, nudging has been used for many applications up to present including research and development of NWP Seaman, 1990, 1991;Seaman et al, 1995;Schraff, 1997;Leidner et al, 2001;Deng et al, 2004;Schroeder et al, 2006), research in the area of hybrid data assimilation methods (Lei et al, 2012a(Lei et al, , 2012b, initialisation of climate runs (Otte et al, 2012;Baehr et al, 2014) and in ocean data assimilation (Chen et al, 2013). Even though it is not mathematically optimal in a least-squares or maximumlikelihood sense, nudging has a good performance-cost ratio that argues for its usability for the purpose of ensemble reanalyses.…”

Section: Analysis Of Atmospheric Variablesmentioning

confidence: 99%

Towards a probabilistic regional reanalysis system for Europe: evaluation of precipitation from experiments

Bach¹,

Schraff²,

Keller³

et al. 2016

Tellus A: Dynamic Meteorology and Oceanography

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A B S T R A C TA new development in the field of reanalyses is the incorporation of uncertainty estimation capabilities. We have developed a probabilistic regional reanalysis system for the CORDEX-EUR11 domain that is based on the numerical weather prediction model COSMO at a 12-km grid spacing. The lateral boundary conditions of all ensemble members are provided by the global reanalysis ERA-Interim. In the basic implementation of the system, uncertainties due to observation errors are estimated. Atmospheric assimilation of conventional observations perturbed by means of random samples of observation error yields estimates of the reanalysis uncertainty conditioned to observation errors. The data assimilation employed is a new scheme based on observation nudging that we denote ensemble nudging. The lower boundary of the atmosphere is regularly updated by external snow depth, sea surface temperature and soil moisture analyses. One of the most important purposes of reanalyses is the estimation of so-called essential climate variables. For regional reanalyses, precipitation has been identified as one of the essential climate variables that are potentially better represented than in other climate data sets. For that reason, we assess the representation of precipitation in our system in a pilot study. Based on two experiments, each of which extends over one month, we conduct a preliminary comparison to the global reanalysis ERAInterim, a dynamical downscaling of the latter and the high-resolution regional reanalysis COSMO-REA6. In a next step, we assess our reanalysis system's probabilistic capabilities versus the ECMWF-EPS in terms of sixhourly precipitation sums. The added value of our probabilistic regional reanalysis system motivates the current production of a 5-year-long test reanalysis COSMO-EN-REA12 in the framework of the FP7-funded project Uncertainties in Ensembles of Regional Re-Analyses (UERRA).

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On the nudging terms at open boundaries in regional ocean models

Cited by 17 publications

References 36 publications

A Novel Modeling Approach to Quantify the Influence of Nitrogen Inputs on the Oxygen Dynamics of the North Sea

A Novel Modeling Approach to Quantify the Influence of Nitrogen Inputs on the Oxygen Dynamics of the North Sea

Looking beyond stratification: a model-based analysis of the biological drivers of oxygen deficiency in the North Sea

Towards a probabilistic regional reanalysis system for Europe: evaluation of precipitation from experiments

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