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- Author or Editor: John W. Wright x
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Abstract
When the wind blows across the water, a highly sheared current develops which extends a few millimeters into the water and amounts, at the surface, to 3–4% of the wind speed. Banner and Phillips (1974) have pointed out that the wind drift, as this thin surface current layer is called, may he sufficiently augmented by interaction with the orbital velocity field of the wave that the maximum particle speed may exceed the phase speed and the wave breaks. If a longer gravity wave is also present, the wind drift may be further augmented and the short gravity wave may break prematurely. We have examined both the basic breaking condition and the diminution (straining) of the short gravity waves by longer waves experimentally in wave tanks. We find that actual wave breaking occurs at substantially higher winds than predicted and that the diminution is substantially less at the higher winds. The observed wind speed dependence of this diminution appears to be contrary to prediction and points to direct coupling between wind and short gravity waves as an important factor in the response of these waves to straining.
Abstract
When the wind blows across the water, a highly sheared current develops which extends a few millimeters into the water and amounts, at the surface, to 3–4% of the wind speed. Banner and Phillips (1974) have pointed out that the wind drift, as this thin surface current layer is called, may he sufficiently augmented by interaction with the orbital velocity field of the wave that the maximum particle speed may exceed the phase speed and the wave breaks. If a longer gravity wave is also present, the wind drift may be further augmented and the short gravity wave may break prematurely. We have examined both the basic breaking condition and the diminution (straining) of the short gravity waves by longer waves experimentally in wave tanks. We find that actual wave breaking occurs at substantially higher winds than predicted and that the diminution is substantially less at the higher winds. The observed wind speed dependence of this diminution appears to be contrary to prediction and points to direct coupling between wind and short gravity waves as an important factor in the response of these waves to straining.
Abstract
The response of the Gulf of Maine region to steady, spatially uniform wind stress is examined using a linearized numerical model, with the influence of the strong tidal currents in the region included in the bottom stress formulation. The sensitivity of the model results to various idealizations is investigated including the assumption of linearity, the bottom steam formulation, cross-shelf structure in the (large-scale) alongshelf wind stress and the cross-shelf boundary conditions. The model solutions for the Gulf are found to be sensitive to the “backward” boundary condition on the Scotian Shelf, but not to the “forward” boundary condition in the Middle Atlantic Bight. For alongshelf stress, the former is estimated using Csanady's “arrested topographic wave” model and observed coastal sea level gains at Halifax.
The model has a spinup time of about one day, comparable to previous estimates for the region. The alongshelf component of wind stress is generally much more effective than the cross-shelf component in driving currents and sea level changes in the model. The predicted large-scale circulation features and coastal sea level changes compare favorably with those observed, and there is reasonable agreement between predicted and observed currents off southwestern Nova Scotia for alongshelf stress. The dynamics of the model response are discussed in terms of the arrested topographic wave model and Ekman dynamics and using the momentum balances at some current meter observation sites.
Abstract
The response of the Gulf of Maine region to steady, spatially uniform wind stress is examined using a linearized numerical model, with the influence of the strong tidal currents in the region included in the bottom stress formulation. The sensitivity of the model results to various idealizations is investigated including the assumption of linearity, the bottom steam formulation, cross-shelf structure in the (large-scale) alongshelf wind stress and the cross-shelf boundary conditions. The model solutions for the Gulf are found to be sensitive to the “backward” boundary condition on the Scotian Shelf, but not to the “forward” boundary condition in the Middle Atlantic Bight. For alongshelf stress, the former is estimated using Csanady's “arrested topographic wave” model and observed coastal sea level gains at Halifax.
The model has a spinup time of about one day, comparable to previous estimates for the region. The alongshelf component of wind stress is generally much more effective than the cross-shelf component in driving currents and sea level changes in the model. The predicted large-scale circulation features and coastal sea level changes compare favorably with those observed, and there is reasonable agreement between predicted and observed currents off southwestern Nova Scotia for alongshelf stress. The dynamics of the model response are discussed in terms of the arrested topographic wave model and Ekman dynamics and using the momentum balances at some current meter observation sites.
Abstract
Three interrelated climate phenomena are at the center of the Climate Variability and Predictability (CLIVAR) Atlantic research: tropical Atlantic variability (TAV), the North Atlantic Oscillation (NAO), and the Atlantic meridional overturning circulation (MOC). These phenomena produce a myriad of impacts on society and the environment on seasonal, interannual, and longer time scales through variability manifest as coherent fluctuations in ocean and land temperature, rainfall, and extreme events. Improved understanding of this variability is essential for assessing the likely range of future climate fluctuations and the extent to which they may be predictable, as well as understanding the potential impact of human-induced climate change. CLIVAR is addressing these issues through prioritized and integrated plans for short-term and sustained observations, basin-scale reanalysis, and modeling and theoretical investigations of the coupled Atlantic climate system and its links to remote regions. In this paper, a brief review of the state of understanding of Atlantic climate variability and achievements to date is provided. Considerable discussion is given to future challenges related to building and sustaining observing systems, developing synthesis strategies to support understanding and attribution of observed change, understanding sources of predictability, and developing prediction systems in order to meet the scientific objectives of the CLIVAR Atlantic program.
Abstract
Three interrelated climate phenomena are at the center of the Climate Variability and Predictability (CLIVAR) Atlantic research: tropical Atlantic variability (TAV), the North Atlantic Oscillation (NAO), and the Atlantic meridional overturning circulation (MOC). These phenomena produce a myriad of impacts on society and the environment on seasonal, interannual, and longer time scales through variability manifest as coherent fluctuations in ocean and land temperature, rainfall, and extreme events. Improved understanding of this variability is essential for assessing the likely range of future climate fluctuations and the extent to which they may be predictable, as well as understanding the potential impact of human-induced climate change. CLIVAR is addressing these issues through prioritized and integrated plans for short-term and sustained observations, basin-scale reanalysis, and modeling and theoretical investigations of the coupled Atlantic climate system and its links to remote regions. In this paper, a brief review of the state of understanding of Atlantic climate variability and achievements to date is provided. Considerable discussion is given to future challenges related to building and sustaining observing systems, developing synthesis strategies to support understanding and attribution of observed change, understanding sources of predictability, and developing prediction systems in order to meet the scientific objectives of the CLIVAR Atlantic program.
