We use a spatially explicit biogeochemical end-to-end ecosystem model, Atlantis, to simulate impacts from the Deepwater Horizon oil spill and subsequent recovery of fish guilds. Dose-response ...relationships with expected oil concentrations were utilized to estimate the impact on fish growth and mortality rates. We also examine the effects of fisheries closures and impacts on recruitment. We validate predictions of the model by comparing population trends and age structure before and after the oil spill with fisheries independent data. The model suggests that recruitment effects and fishery closures had little influence on biomass dynamics. However, at the assumed level of oil concentrations and toxicity, impacts on fish mortality and growth rates were large and commensurate with observations. Sensitivity analysis suggests the biomass of large reef fish decreased by 25% to 50% in areas most affected by the spill, and biomass of large demersal fish decreased even more, by 40% to 70%. Impacts on reef and demersal forage caused starvation mortality in predators and increased reliance on pelagic forage. Impacts on the food web translated effects of the spill far away from the oiled area. Effects on age structure suggest possible delayed impacts on fishery yields. Recovery of high-turnover populations generally is predicted to occur within 10 years, but some slower-growing populations may take 30+ years to fully recover.
Continued advances in computational resources are providing the opportunity to operate more sophisticated numerical models. Additionally, there is an increasing demand for multidisciplinary studies ...that include interactions between different physical processes. Therefore there is a strong desire to develop coupled modeling systems that utilize existing models and allow efficient data exchange and model control. The basic system would entail model “1” running on “M” processors and model “2” running on “N” processors, with efficient exchange of model fields at predetermined synchronization intervals. Here we demonstrate two coupled systems: the coupling of the ocean circulation model Regional Ocean Modeling System (ROMS) to the surface wave model Simulating WAves Nearshore (SWAN), and the coupling of ROMS to the atmospheric model Coupled Ocean Atmosphere Prediction System (COAMPS). Both coupled systems use the Model Coupling Toolkit (MCT) as a mechanism for operation control and inter-model distributed memory transfer of model variables. In this paper we describe requirements and other options for model coupling, explain the MCT library, ROMS, SWAN and COAMPS models, methods for grid decomposition and sparse matrix interpolation, and provide an example from each coupled system. Methods presented in this paper are clearly applicable for coupling of other types of models.
Abstract
Air–sea coupling during coastal upwelling was examined through idealized three-dimensional numerical simulations with a coupled atmosphere–ocean mesoscale model. Geometry, topography, and ...initial and boundary conditions were chosen to be representative of summertime coastal conditions off the Oregon coast. Over the 72-h simulations, sea surface temperatures were reduced several degrees near the coast by a wind-driven upwelling of cold water that developed within 10–20 km off the coast. In this region, the interaction of the atmospheric boundary layer with the cold upwelled water resulted in the formation of an internal boundary layer below 100-m altitude in the inversion-capped boundary layer and a reduction of the wind stress in the coupled model to half the offshore value. Surface heat fluxes were also modified by the coupling. The simulated modification of the atmospheric boundary layer by ocean upwelling was consistent with recent moored and aircraft observations of the lower atmosphere off the Oregon coast during the upwelling season. For these 72-h simulations, comparisons of coupled and uncoupled model results showed that the coupling caused measurable differences in the upwelling circulation within 20 km off the coast. The coastal Ekman transport divergence was distributed over a wider offshore extent and a thinner ocean surface boundary layer, with consistently smaller offshore and depth-integrated alongshore transport formed in the upwelling region, in the coupled case relative to the uncoupled case. The results indicate that accurate models of coastal upwelling processes can require representations of ocean–atmosphere interactions on short temporal and horizontal scales.
Abstract
A substantial role for atmospheric noise in simulations of decadal internal variability of SST is demonstrated by a comparison of a multicentury climate model control and a corresponding ...interactive ensemble (IE) simulation. The IE is designed to reduce atmospheric noise in the heat flux, wind stress, and freshwater flux at the air–sea interface. This comparison suggests that nearly all SST variability on decadal time scales is forced by internal atmospheric variability. The results are examined to determine the relative roles of atmospheric surface heat flux noise and ocean dynamics in the decadal volume-averaged heat budget of the upper ocean. The regional heat budgets in two regions, the South Pacific and the midlatitude North Atlantic, show the net atmospheric surface heat flux to be approximately in equilibrium with the ocean dynamics forcing. The IE and control results are used in the equilibrium heat budget approximation to infer the atmospheric heat flux response to SST, as well as the time series of the control atmospheric noise surface heat flux and ocean dynamics forcings for several regions. The South Pacific region SST is found to be primarily forced by the atmospheric noise surface heat flux and the North Atlantic region SST is forced by the ocean dynamics. Similar strengths for the atmospheric heat flux noise and ocean dynamics forcing, with an interdecadal atmospheric heat flux noise time scale and a centennial ocean dynamics time scale, are found for an Atlantic multidecadal variability region SST.
Abstract
We analyze the role of mesoscale heat advection in a mixed layer (ML) heat budget, using a regional high-resolution coupled model with realistic atmospheric forcing and an idealized ocean ...component. The model represents two regions in the Southern Ocean, one with strong ocean currents and the other with weak ocean currents. We conclude that heat advection by oceanic currents creates mesoscale anomalies in sea surface temperature (SST), while the atmospheric turbulent heat fluxes dampen these SST anomalies. This relationship depends on the spatial scale, the strength of the currents, and the mixed layer depth (MLD). At the oceanic mesoscale, there is a positive correlation between the advection and SST anomalies, especially when the currents are strong overall. For large-scale zonal anomalies, the ML-integrated advection determines the heating/cooling of the ML, while the SST anomalies tend to be larger in size than the advection and the spatial correlation between these two fields is weak. The effects of atmospheric forcing on the ocean are modulated by the MLD variability. The significance of Ekman advection and diabatic heating is secondary to geostrophic advection except in summer when the MLD is shallow. This study links heat advection, SST anomalies, and air–sea heat fluxes at ocean mesoscales, and emphasizes the overall dominance of intrinsic oceanic variability in mesoscale air–sea heat exchange in the Southern Ocean.
Coupling between the atmosphere and ocean is scale-dependent. For example, in the mid-latitudes and at oceanic mesoscales (spatial scales between 10 and hundreds of kilometers), the air–sea ...interactions are driven by the oceanic variability, and the atmosphere responds to the changes in the sea surface temperature anomalies (SSTA), which are created by fast oceanic advection. This study explores these interactions, using a regional high-resolution atmosphere–ocean coupled model with a realistic atmospheric component and a semi-idealized oceanic model of a zonal flow. The atmospheric component consists of two nested domains: the inner domain fully coupled with the ocean model, and the outer domain one-way coupled with the observed SST. Two 2-year simulations are discussed here: one in which the oceanic isopycnals are steep and ocean currents are strong (“Strong Currents” or SC) and another with less steep isopycnals and weaker currents (“Weak Currents” or WC). Simulated mesoscale variability occurs on a wide range of spatial scales, and we distinguish large-mesoscale (hundreds of kilometers and shorter) and small-mesoscale (tens of kilometers and shorter) anomalies. The model is most applicable to the mid-latitude Southern Ocean far from any boundaries.
Relationships between atmospheric variables and SSTA are studied using temporal correlations and coupling coefficients, and for both large-mesoscale and small-mesoscale anomalies. Significant positive correlations between large-mesoscale anomalies are found for following pairs of variables: equivalent neutral stability (ENS) 10-meter winds and SSTA, wind stress and SSTA, and wind stress divergence/curl and SSTA downwind/crosswind gradients. The temporal correlations are smaller for the small-mesoscale anomalies. The correlation coefficients are also higher for the model SC region, whereas the corresponding coupling coefficients are higher in the model WC region. Among all pairs, the coupling coefficients for the ENS winds and SSTA are the most consistent in time and various environmental conditions. Coupling coefficients for the wind stress and SSTA show a nearly linear dependence on the ENS wind speed. As a result, the reported variability in these coupling coefficients indicates a complex, nonlinear relationship between the wind and SST anomalies. Our numerical analysis indicates strong presence of the Vertical Mixing Mechanism involving the downward momentum mixing on both small- and large-mesoscales. In contrast, the active presence of the Pressure Adjustment Mechanism in the Marine Boundary Layer could not be confirmed on the spatial and time scales considered in this study.
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•A regional model combines a realistic atmosphere and an idealized ocean component.•Two Southern Ocean regions with very different densities and velocities are studied.•The relationship between the winds and SST is studied using coupling coefficients.•The coupling coefficients depend on the region and scales of the SST anomalies.•Vertical Mixing Mechanism is important at both small- and large-mesoscales.•The importance of the Pressure Adjustment Mechanism is not confirmed.
Ocean variability is a dominant source of remote rainfall predictability, but in many cases the physical mechanisms driving this predictability are not fully understood. This study examines how ocean ...mesoscales (i.e., the Gulf Stream SST front) affect decadal Southeast US (SEUS) rainfall, arguing that the local imprint of large‐scale teleconnections is sensitive to resolved mesoscale features. Based on global coupled model experiments with eddying and eddy‐parameterizing ocean, we find that a resolved Gulf Stream improves localized rainfall and remote circulation response in the SEUS. The eddying model generally improves the air‐sea interactions in the Gulf Stream and the North Atlantic Subtropical High that modulate SEUS rainfall over decadal timescales. The eddy‐parameterizing simulation fails to capture the sharp SST gradient associated with the Gulf Stream and overestimates the role of tropical Pacific SST anomalies in the SEUS rainfall.
Plain Language Summary
Current global climate models (GCMs) typically fail to fully resolve mesoscale ocean features (with length scales on the order of 10 km) such as western boundary currents, which potentially limit rainfall predictability over decadal timescales. Improvements in high‐performance climate modeling enable us to incorporate high‐resolution ocean models (0.1°) that capture these important mesoscale features with increased fidelity. Here we show that the inclusion of mesoscale ocean processes produces a more realistic Gulf Stream and improves both localized rainfall patterns and large‐scale teleconnections. The high‐resolution model shows a better representation of the air‐sea interactions between the sea surface temperature and low‐level atmosphere over the Gulf Stream, thus improving low‐frequency rainfall variations over the Southeast US. The results further imply that high‐resolution GCMs with increased ocean model resolution may be needed in future climate prediction systems.
Key Points
Decadal rainfall pattern and associated mechanism in the Southeast US are examined from an eddying global coupled model
Eddying CCSM4 improves the air‐sea interactions in the Gulf Stream and the North Atlantic Subtropical High, modulating Southeast US rainfall
Eddy‐parameterizing CCSM4 and CMIP5 models may overestimate the role of tropical sea surface temperature in decadal Southeast US rainfall
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