摘要:

AbstractA composite time series of the merged satellite altimeters sea surface height anomaly (SSHA) data and satellite‐observed sea surface temperature (SST) data were used to identify eddies in the Western North Pacific Ocean (WNPO), where there were numbers of intense typhoons. This study systematically investigated 15 super typhoons during the period of 2000‐2008 in the WNPO to study their impacts on the pre‐typhoon ocean features, e.g., the cyclonic ocean eddy (COE) feature (closed contours of SSHA<−6 cm) and neutral condition (SSHA between −6 and 6 cm). Two new COEs are generated by two super typhoons, and 18 pre‐existing COEs are intensified by 13 super typhoons. 5 of the 13 super typhoons each influenced two pre‐exisiting COEs. Although the typhoon‐induced maximum cooling centers had a right bias along the tracks due to wind conditions, pre‐existing COEs also play a significant role in determining the strength and location of large SST cooling. Three possible factors (maximum wind speed, typhoon translation speed and the typhoon forcing time,Tf) are employed to explain the interactions. Above all, the changes of the COE geometric and physical parameters (e.g., effective radius, area, SST, SSHA, and eddy kinetic energy) were mostly related to the typhoon forcing time,Tf. This is becauseTfis a parameter that is a combination of the typhoon's translation speed, intensity and size. Although the typhoons may significantly impact COEs, such samples were not commonly observed. Thus, the impact of typhoon on the strength of COEs is gene

ISSN:0148-0227    

DOI:10.1002/2013JC009575

年代:2014

数据来源: WILEY

摘要:

AbstractWe incorporate a physically derived parameterization of gravity drainage, in terms of a convective upwelling velocity, into a one‐dimensional, thermodynamic sea‐ice model of the kind currently used in coupled climate models. Our parameterization uses a local Rayleigh number to represent the important feedback between ice salinity, porosity, permeability, and desalination rate. It allows us to determine salt fluxes from sea ice and the corresponding evolution of the bulk salinity of the ice, in contrast to older, established models that prescribe the ice salinity. This improves the predictive power of climate models in terms of buoyancy fluxes to the polar oceans, and also the thermal properties of sea ice, which depend on its salinity. We analyze the behavior of existing fixed‐salinity models, elucidate the physics by which changing salinity affects ice growth and compare against our dynamic‐salinity model, both in terms of laboratory experiments and also deep‐ocean calculations. These comparisons explain why the direct effect of ice salinity on growth is relatively small (though not always negligible, and sometimes different from previous studies), and also highlight substantial differences in the qualitative pattern and quantitative magnitude of salt fluxes into the polar oceans. Our study is particularly relevant to growing first‐year ice, when gravity drainage is the dominant mechanism by which ice desalinates. We expect that our dynamic model, which respects the underlying physics of brine drainage, should be more robust to changes in polar climate and more responsive to rapid changes in oceanic and atmosphe

ISSN:0148-0227    

DOI:10.1002/2013JC009296

年代:2014

数据来源: WILEY

摘要:

AbstractWe examine the oceanic impact of large tropical volcanic eruptions as they appear in ensembles of historical simulations from eight Coupled Model Intercomparison Project Phase 5 models. These models show a response that includes lowering of global average sea surface temperature by 0.1–0.3 K, comparable to the observations. They show enhancement of Arctic ice cover in the years following major volcanic eruptions, with long‐lived temperature anomalies extending to the middepth and deep ocean on decadal to centennial timescales. Regional ocean responses vary, although there is some consistent hemispheric asymmetry associated with the hemisphere in which the eruption occurs. Temperature decreases and salinity increases contribute to an increase in the density of surface water and an enhancement in the overturning circulation of the North Atlantic Ocean following these eruptions. The strength of this overturning increase varies considerably from model to model and is correlated with the background variability of overturning in each model. Any cause/effect relationship between eruptions and the phase of El Niño is

ISSN:0148-0227    

DOI:10.1002/2013JC009780

年代:2014

数据来源: WILEY

摘要:

AbstractWe investigated sea surface total alkalinity (TAlk), dissolved inorganic carbon (DIC), dissolved oxygen (DO), and satellite‐derived chlorophyll‐a in the connection between the Yellow Sea and the East China Sea (ECS) during April to early May 2007. In spring, Changjiang dilution water (CDW), ECS offshore water, and together with Yellow Sea water (YSW) occupied the northern ECS. Using 16 day composite satellite‐derived chlorophyll‐a images, several algal blooms were identified in the CDW and ECS offshore water. Correspondingly, biological DIC drawdown of 73 ± 20 μmol kg−1, oversaturated DO of 10–110 μmol O2kg−1, and low fugacity of CO2of 181–304 μatm were revealed in these two waters. YSW also showed CO2uptake in spring, due to the very low temperature. However, its intrusion virtually counteracted CO2uptake in the northern ECS. In the CDW and the ECS offshore water, Revelle factor was 9.3–11.7 and 8.9–10.6, respectively, while relatively high Revelle factor values of 11.4–13.0 were revealed in YSW. In the ECS offshore water, the observed relationship between DIC drawdown and oversaturated DO departed from the Redfield ratio, indicating an effect of chemical buffering capacity on the carbonate system during air‐sea reequilibration. Given the fact that the chemical buffering capacity slows down the air‐sea reequilibration of CO2, the early spring DIC drawdown may have durative effects on the sea surface carbonate system until early summer. Although our study is subject to limited temporal and spatial coverage of sampling, these insights are fundamental to understanding sea surface carbonate chemistry dynami

ISSN:0148-0227    

DOI:10.1002/2014JC009856

年代:2014

数据来源: WILEY

摘要:

AbstractIn this study, we investigate the subsurface salinity changes on decadal timescales across the subtropical South Atlantic Ocean using two ocean reanalysis products, the latest version of the Simple Ocean Data Assimilation and the Estimating the Circulation and Climate of the Ocean, Phase II, as well as using additional climate model experiments. Results show that there is a recent significant salinity increase at the core of the salinity minimum at intermediate levels. The main underlying mechanism for this subsurface salinity increase is the lateral advective (gyre) changes due to the Southern Annular Mode variability, which conditions an increased contribution from the Indian Ocean high salinity waters into the Atlantic. The global warming signal has a secondary but complementary contribution. Latitudinal differences at intermediate depth in response to large‐scale forcing are in part caused by local variation of westward propagation features, and by compensating contributions of salinity and temperature to density change

ISSN:0148-0227    

DOI:10.1002/2014JC009812

年代:2014

数据来源: WILEY

摘要:

AbstractInterannual to decadal sea level variability on the North Atlantic western boundary is surprisingly coherent over substantial distances stretching from the Caribbean to Nova Scotia. The physical mechanisms responsible for this basin‐scale, low‐frequency coherence are explored in a diagnosis of simulated ocean fields from GECCO, which reproduces the observations to good approximation. Coastal sea level variability on the western boundary is known to be influenced by meridional divergence in the boundary current resulting in a geostrophic tilting of the sea surface. This mechanism is found to be of leading order along some stretches of the boundary, but it does not account for the coherence spanning the western North Atlantic. Instead, the coherence along the entire boundary is accounted for by vertical divergence resulting in the uniform rise and fall of the sea surface west of the 295°E meridian. The vertical divergence is found to be due to net vertically integrated zonal transport across this meridian resulting from meridional variation in the Sverdrup transport over the basin inte

ISSN:0148-0227    

DOI:10.1002/2014JC009999

年代:2014

数据来源: WILEY

摘要:

AbstractWe investigate spreading pathways of basal meltwater released from all Antarctic ice shelves using a circumpolar coupled ice shelf‐sea ice‐ocean model that reproduces major features of the Southern Ocean circulation, including the Antarctic Circumpolar Current (ACC). Several independent virtual tracers are used to identify detailed pathways of basal meltwaters. The spreading pathways of the meltwater tracers depend on formation sites, because the meltwaters are transported by local ambient ocean circulation. Meltwaters from ice shelves in the Weddell and Amundsen‐Bellingshausen Seas in surface/subsurface layers are effectively advected to lower latitudes with the ACC. Although a large portion of the basal meltwaters is present in surface and subsurface layers, a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the Antarctic coastal margins. The signals at the seafloor extend along the topography, showing a horizontal distribution similar to the observed spreading of Antarctic Bottom Water. Meltwaters originating from ice shelves in the Weddell and Ross Seas and in the Indian sector significantly contribute to the bottom signals. A series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and/or ocean thermohaline circulation in the Southern

ISSN:0148-0227    

DOI:10.1002/2014JC009915

年代:2014

数据来源: WILEY

摘要:

AbstractThis numerical investigation examines buoyancy‐driven circulation on the Texas‐Louisiana shelf modulated by seasonal winds. In wintertime, with downcoast (in the direction of Kelvin wave propagation) wind forcing, the Mississippi‐Atchafalaya River plume exhibits a bottom‐advected pattern. The plume is fairly wide and the horizontal density gradients span almost across the entire shelf inshore of 50 m. Within the plume, vertical shear of alongshore flow is in thermal wind balance with the cross‐shore density gradient, and the shear causes a slight reversal of alongshore flow near the bottom. An alongshore flow estimated by the thermal wind relation, along with an assumption of zero bottom velocity, generally well agrees with the actual flow near the surface in regions deeper than 20 m. In spring and summer, the thermal‐wind‐balance‐derived flow deviates from the actual alongshore flow, and an Ekman flow driven by strong onshore wind makes the major contribution to the deviation. Besides, the summertime upcoast wind component transforms the plume to a surface‐advected state, resulting in reduced cross‐shore density gradients and increasing the relative importance of wind‐driven, barotropic alongshore flow, which contributes to th

ISSN:0148-0227    

DOI:10.1002/2013JC009763

年代:2014

数据来源: WILEY

摘要:

AbstractPredicting tides in upstream reaches of rivers is a challenge, because tides are highly nonlinear and nonstationary, and accurate short‐time predictions of river flow are hard to obtain. In the St. Lawrence fluvial estuary, tide forecasts are produced using a one‐dimensional model (ONE‐D), forced downstream with harmonic constituents, and upstream with daily discharges using 30 day flow forecasts from Lake Ontario and the Ottawa River. Although this operational forecast system serves its purpose of predicting water levels, information about nonstationary tidal‐fluvial processes that can be gained from it is limited, particularly the temporal changes in mean water level and tidal properties (i.e., constituent amplitudes and phases), which are function of river flow and ocean tidal range. In this paper, a harmonic model adapted to nonstationary tides, NS_TIDE, was applied to the St. Lawrence fluvial estuary, where the time‐varying external forcing is directly built into the tidal basis functions. Model coefficients from 13 analysis stations were spatially interpolated to allow tide predictions at arbitrary locations as well as to provide insights into the spatiotemporal evolution of tides. Model hindcasts showed substantial improvements compared to classical harmonic analyses at upstream stations. The model was further validated by comparison with ONE‐D predictions at a total of 32 stations. The slightly lower accuracy obtained with NS_TIDE is compensated by model simplicity, efficiency, and capacity to represent stage and tidal variations in a very compact way and thus represents a new means for understanding t

ISSN:0148-0227    

DOI:10.1002/2014JC009791

年代:2014

数据来源: WILEY

摘要:

AbstractThe interannual variability of the eastward current in the western South China Sea (SCS) during the summer of 1993–2012 is examined with satellite altimeter data and Regional Ocean Modeling System (ROMS) model output. It is found that the meridional location of the eastward current displays apparent interannual variability. The core of the eastward current shifts between 10.7°N and 17.6°N with a standard deviation of 1.6°. Results from Sverdrup theory and ROMS experiments demonstrate a close dynamic linkage between the north‐south migration of the eastward current and the SCS summer monsoon anomaly on the interannual time scale. When the summer monsoon has southwesterly (northeasterly) anomaly, the eastward current moves southward (northward). With the southward (northward) shift of the eastward current, the summer cold filament in the SCS moves southward (northward) a

ISSN:0148-0227    

DOI:10.1002/2014JC010309

年代:2014

数据来源: WILEY