摘要:

The heat and mass balance of the Arctic Ocean is very sensitive to the growth and decay of sea ice and the interaction between the heat and salt fields in the oceanic boundary layer. The hydraulic roughness of sea ice controls the detailed nature of turbulent fluxes in the boundary layer and hence is an important ingredient in model parameterizations. We describe a novel mechanism for the generation of corrugations of the sea ice–ocean interface, present a mathematical analysis elucidating the mechanism, and present numerical calculations for geophysically relevant conditions. The mechanism relies on brine flows developing in the sea ice due to Bernoulli suction by flow of ocean past the interface. For oceanic shears at the ice interface of 0.2 s−1, we expect the corrugations to form with a wavelength dependent upon the permeability structure of the sea ice which is described herein. The mechanism should be particularly important during sea ice formation in wind‐maintained coastal polynyas and in leads. This paper applies our earlier analyses of the fundamental instability to field conditions and extends it to take account of the anisotropic and heterogeneous permeability of se

ISSN:0148-0227    

DOI:10.1029/2000JC000559

年代:2002

数据来源: WILEY

摘要:

The intrusion of open ocean water across the head of DeSoto Canyon offshore of Pensacola, Florida, is investigated using a version of the Bryan‐Cox model of the entire Gulf of Mexico. The Loop Current‐forced model circulation in DeSoto Canyon features an eastward, nearly along‐isobath, current with a weak cross‐isobath velocity component. In contrast, the southward wind‐driven currents over the west Florida shelf in response to northerly winds induce strong cross‐isobath flow at the head of DeSoto Canyon. The flow is diagnosed to be the bottom Ekman flow associated with the strong along‐isobath currents. In addition, transient responses of sea levels to the northerly wind bursts give rise to pressure gradient‐forced currents up the canyon during the collapse phase of the winds. A case study in November 1997 is conducted, and the above arguments are substantiated with the simulated and the ob

ISSN:0148-0227    

DOI:10.1029/2001JC000793

年代:2002

数据来源: WILEY

摘要:

To date, flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow, with vegetative drag treated as an extension of bed drag. However, recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer. This paper presents laboratory measurements, obtained from a scaled seagrass model, that demonstrate the applicability of the mixing layer analogy to aquatic systems. Specifically, all vertical profiles of mean velocity contained an inflection point, which makes the flow susceptible to Kelvin‐Helmholtz instability. This instability leads to the generation of large, coherent vortices within the mixing layer (observed in the model at frequencies between 0.01 and 0.11 Hz), which dominate the vertical transport of momentum through the layer. The downstream advection of these vortices is shown to cause the progressive, coherent waving of aquatic vegetation, known as the monami. When the monami is present, the turbulent vertical transport of momentum is enhanced, with turbulent stresses penetrating an additional 30% of the plant height into the canop

ISSN:0148-0227    

DOI:10.1029/2001JC000871

年代:2002

数据来源: WILEY

摘要:

Accurate geoids are expected to improve our knowledge of the dynamic sea surface height (SSH) as a mirror of the dynamic state of the oceans. The dedicated Gravity Field and Steady‐State Ocean Circulation Explorer (GOCE) mission will lead to a highly accurate geoid model with a resolution of degree and order 200. We examine the impact of this mission on the assessment of large‐scale oceanic mass and heat transports via its expected error characteristics. We do so applying a linear box inverse model and a nonlinear section inverse model to hydrographic data and to (synthetic) SSH data. The results are compared to those obtained when substituting the error estimates of the Gravity Recovery and Climate Experiment (GRACE) mission and the present‐day Earth Gravitational Model 1996. For the box inverse model we find an average reduction in transport uncertainties of about 9% for GRACE geoid error covariances and about 17% for GOCE over the “hydrography‐only” solution. In both GRACE and GOCE these average percentage improvements are significantly increased when model error is excluded. Summarizing our results and those of the companion parts of this study, we conclude that the GRACE mission reduces the marine geoid uncertainties such that altimetry may become useful for the study of the steady state ocean circulation. The GOCE mission will improve the accuracy of the circulation estimates significantly on the large scales and introduce higher accuracy on shorter wavelengths as well. Furthermore, it will enable us to study individual oce

ISSN:0148-0227    

DOI:10.1029/2000JC000647

年代:2002

数据来源: WILEY

摘要:

The surface heat budget over the Weddell Sea ice cover in 1996 was studied on the basis of data from Argos buoys equipped with meteorological sensors. In addition, a thermodynamic sea ice model, satellite‐based data on the sea ice concentration, sonar results on ice thickness distribution, and output from large‐scale meteorological models were all utilized. Applying the buoy data, the sensible heat flux over sea ice was calculated by Monin‐Obukhov theory using the gradient method, and the latent heat flux was obtained by the bulk method. A second estimate for the surface fluxes was obtained from the thermodynamic sea ice model, which was forced by the buoy observations. The results showed a reasonable agreement. The dominating component in the heat budget over ice was the net longwave radiation, which had a mean annual cooling effect of −28 W m−2. This was balanced by the net shortwave radiation (annual mean 13 W m−2), the sensible (13 W m−2) and latent (−3 W m−2) heat fluxes, and the conductive heat flux through the ice (5 W m−2). The regional surface fluxes over the fractured ice cover were estimated using the buoy data and Special Sensor Microwave Imager (SSMI)‐derived ice concentrations. In winter the regional surface sensible heat flux was sensitive to the ice concentration and thickness distribution. The estimate for the area‐averaged formation rate of new ice in leads in winter varies from 0.05 to 0.21 m per month depending on the SSMI processing algorithm applied. Countergradient fluxes occurred 8–10% of the time. The buoy observations were compared with the operational analyses of the European Centre for Medium‐Range Weather Forecasts (ECMWF) and the reanalyses of the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR). The 2 m air temperature and surface temperature were 3.5° and 4.4°C too high, respectively, in the ECMWF and 3.2° and 3.0°C too low in the NCEP/NCAR fields, but the models reproduced the synoptic‐scale temperature variations well. The errors seem to be related to the cloud cover and the surface boundary conditions. Neither of the models recognizes leads in the ice pack, and the ice and snow thicknesses are often far from reality. The distribution of the cloud cover in the both models

ISSN:0148-0227    

DOI:10.1029/2000JC000372

年代:2002

数据来源: WILEY

摘要:

Comparison of ocean buoy observations and model calculations of incoming clear‐sky surface shortwave radiation is performed in order to assess the buoys' general reliability under operating conditions. The buoy data employed for this study come from several experimental and operational deployments conducted by Woods Hole Oceanographic Institution (WHOI) and Pacific Marine Environmental Laboratory (PMEL). WHOI deployments include the Frontal Air‐Sea Interaction Experiment, Marine Light Mixed Layer Experiment, Coupled Ocean‐Atmosphere Response, Subduction Experiment, Arabian Sea Experiment, Pan‐American Climate Study, and Biowatt. PMEL deployments include the Tropical Atmosphere Ocean moored buoy array in the tropical Pacific Ocean. These moorings and their associated shortwave measurements represent the vast majority of open‐ocean in situ shortwave observations available to date. Two separate schemes were used to filter the cloudy samples from the buoy shortwave time series, one based on satellite values of cloudiness and a second scheme based on the buoy observations themselves and on a number of additional constraints. The clear‐sky model calculations of surface shortwave were computed using the single‐column radiation code from the National Center for Atmospheric Research Community Climate Model, version 3. The primary uncertainty associated with the model calculations is the specification of the aerosol amount. In general, there was a fairly high level of agreement between the buoy and modeled values of clear‐sky surface shortwave. However, there were a few buoys that exhibited significant model‐data discrepancies (e.g., model‐data biases exceeding 10%, or ∼40 W m−2). The possible reasons for these discrepancies were investigated. In some cases, unaccounted for aerosol variability in the model was found to be the most probable cause, indicating that observations were likely to be reliable. In other cases, the discrepancies appeared to result from sensor tilt associated with wind, currents, or deployment/mounting problems and/or were possibly due to aeroso

ISSN:0148-0227    

DOI:10.1029/2000JC000558

年代:2002

数据来源: WILEY