The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform
Peter N Blossey - One of the best experts on this subject based on the ideXlab platform.
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the dissipation of Trapped lee Waves part ii the relative importance of the boundary layer and the stratosphere
Journal of the Atmospheric Sciences, 2016Co-Authors: Matthew O G Hills, Dale R. Durran, Peter N BlosseyAbstract:AbstractDecaying Trapped Waves exert a drag on the large-scale flow. The two most studied mechanisms for such decay are boundary layer dissipation and leakage into the stratosphere. If the Waves dissipate in the boundary layer, they exert a drag near the surface, whereas, if they leak into the stratosphere, the drag is exerted at the level where the Waves dissipate aloft. Although each of these decay mechanisms has been studied in isolation, their relative importance has not been previously assessed.Here, numerical simulations are conducted showing that the relative strength of these two mechanisms depends on the details of the environment supporting the Waves. During actual Trapped-Wave events, the environment often includes elevated inversions and strong winds aloft. Such conditions tend to favor leakage into the stratosphere, although boundary layer dissipation becomes nonnegligible in cases with shorter resonant Wavelengths and higher tropopause heights. In contrast, idealized two-layer profiles with ...
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the dissipation of Trapped lee Waves part i leakage of inviscid Waves into the stratosphere
Journal of the Atmospheric Sciences, 2015Co-Authors: Dale R. Durran, Matthew O G Hills, Peter N BlosseyAbstract:AbstractLeaky Trapped mountain lee Waves are investigated by examining the structure of individual linear modes in multilayer atmospheres. When the static stability and cross-mountain wind speed are constant in the topmost unbounded layer, modes that decay exponentially downstream also grow exponentially with height. This growth with height occurs because packets containing relatively large-amplitude Waves follow ray paths through the stratosphere, placing them above packets entering the stratosphere farther downstream that contain relatively low-amplitude Waves. Nevertheless, if the Trapped Wave train is generated by a compact source, all Waves disappear above some line parallel to the group velocity that passes just above the source region.The rate of downstream decay due to leakage into the stratosphere is strongly dependent on the atmospheric structure. Downstream dissipation is often significant under realistic atmospheric conditions, which typically include elevated inversions and strong upper-tropo...
Barbara M. Hickey - One of the best experts on this subject based on the ideXlab platform.
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coastal Trapped Waves alongshore pressure gradients and the california undercurrent
Journal of Physical Oceanography, 2014Co-Authors: Thomas P Connolly, Barbara M. Hickey, Igor Shulman, Richard E ThomsonAbstract:AbstractThe California Undercurrent (CUC), a poleward-flowing feature over the continental slope, is a key transport pathway along the west coast of North America and an important component of regional upwelling dynamics. This study examines the poleward undercurrent and alongshore pressure gradients in the northern California Current System (CCS), where local wind stress forcing is relatively weak. The dynamics of the undercurrent are compared in the primitive equation Navy Coastal Ocean Model and a linear coastal Trapped Wave model. Both models are validated using hydrographic data and current-meter observations in the core of the undercurrent in the northern CCS. In the linear model, variability in the predominantly equatorward wind stress along the U.S. West Coast produces episodic reversals to poleward flow over the northern CCS slope during summer. However, reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south ...
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circulation over the santa monica san pedro basin and shelf
Progress in Oceanography, 1992Co-Authors: Barbara M. HickeyAbstract:Abstract The spatial and temporal structure of the circulation in Santa Monica-San Pedro basin and over the adjacent mainland shelf has been described in a series of experiments that included moored arrays of currents meters, hydrographic surveys, satellite-derived sea surface temperature maps and Lagrangian drifter deployments. This basin, located in the Southern California Bight adjacent to the coast, is roughly 100km long, 40km wide and 900m deep. From the sea surface to a depth of about 250m, the basin is open to the San Diego Trough to the southeast, the Santa Barbara Channel to the northwest, and the Santa Cruz basin to the west. The resulting data set is the first spatially comprehensive data set over the continental slope of the US west coast, the first comprehensive data set in a coastal region of such complicated topography, and the first that includes detailed measurements over a semi-enclosed shelf, namely, Santa Monica bay. The most significant contributions of the research based on this data set are: (1) demonstration of the alteration of a low mode coastal-Trapped Wave by a sharp bend in topography; (2) demonstration that fluctuating currents on a semi-enclosed shelf can be driven by the flow along its open boundary; (3) demonstration that topographic Waves exist in the completely enclosed portion of coastal basins. In addition, the research allowed an order of magnitude improvements in regional knowledge of both the seasonal and subtidal scale fluctuations within the Southern California Bight. For example, on seasonal scales, the winter surfacing of the California undercurrent (the dominant feature of the seasonal mean flow field) as well as the continuity of the undercurrent in a spatially limited region were addressed. The existence of an equatorward undercurrent at mid water column depths (300–500m) over the continental slope during the late summer to fall season was also documented. On subtidal scales, the data demonstrated that the velocity field is far from “quiescent” over the basin, even below the depth of the deepest basin sill. Spatially-organized subtidal fluctuations occur at all depths and the time scale of the dominant fluctuations (∼ 20–30d) is a factor of two or more longer than that typical of most coastal shelves. The fluctuations have a subsarface maximum during most of the year and the maximum is best developed in late summer and over the mainland slope of the basin. Propagation characteristics south of the basin and within the basin along its coastal perimeter are consistent with those of first mode freely propagating coastal-Trapped Waves at these long periods. The long period Waves enter the basin from southeast and then appear to pivot conterclockwise around the basin, so that at least some porion of the Waves exits the basin over its western sill. The phase speed of the Waves is reduced by an order of magnitude over all but the coastal slope of the basin. Below sill-depth velocity and temperature fluctuations appear to be the signature of freely propagating basin-scale topographic Waves driven by the long period upper water column fluctuations. The Waves travel counterclockwise around the lower basin at speeds about 25cm s −1 . Current fluctuations over the adjacent inner Santa Monica shelf have significant variance at shorter periods as well as at the longer periods observed over the basin and its slopes. These fluctuations are driven predominantly by boundary forcing over the outer shelf and only secondary by local wind stress. Wind data suggests that although local upwelling within the Bight is extremely limited from late spring through fall, strong upwelling events occur routinely in winter early spring. During the summer to fall months effects of upwelling may be experienced within the Bight, but these effects are primarily the results of upwelling outside the Bight in combination with lateral advection. During periods of strong upwelling outside the Bigth, outflow from Santa Monica basin appears to be preferentially directed south of the Channel Islands rather than through the Santa Barbara Channel.
Richard E Thomson - One of the best experts on this subject based on the ideXlab platform.
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coastal Trapped Waves alongshore pressure gradients and the california undercurrent
Journal of Physical Oceanography, 2014Co-Authors: Thomas P Connolly, Barbara M. Hickey, Igor Shulman, Richard E ThomsonAbstract:AbstractThe California Undercurrent (CUC), a poleward-flowing feature over the continental slope, is a key transport pathway along the west coast of North America and an important component of regional upwelling dynamics. This study examines the poleward undercurrent and alongshore pressure gradients in the northern California Current System (CCS), where local wind stress forcing is relatively weak. The dynamics of the undercurrent are compared in the primitive equation Navy Coastal Ocean Model and a linear coastal Trapped Wave model. Both models are validated using hydrographic data and current-meter observations in the core of the undercurrent in the northern CCS. In the linear model, variability in the predominantly equatorward wind stress along the U.S. West Coast produces episodic reversals to poleward flow over the northern CCS slope during summer. However, reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south ...
E R Johnson - One of the best experts on this subject based on the ideXlab platform.
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meanders and eddies from topographic transformation of coastal Trapped Waves
Journal of Physical Oceanography, 2014Co-Authors: J T Rodney, E R JohnsonAbstract:AbstractThis paper describes how topographic variations can transform a small-amplitude, linear, coastal-Trapped Wave (CTW) into a nonlinear Wave or an eddy train. The dispersion relation for CTWs depends on the slope of the shelf. Provided the cross-shelf slope varies sufficiently slowly along the shelf, the local structure of the CTW adapts to the local geometry and the Wave transformation can be analyzed by the Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) method. Two regions of parameter space are straightforward: adiabatic transmission (where, at the incident Wave frequency, a long Wave exists everywhere along the shelf) and short-Wave reflection (where somewhere on the shelf no long Wave exists at the incident frequency, but the stratification is sufficiently weak that a short reflected Wave can coexist with the incident Wave). This paper gives the solutions for these two cases but concentrates on a third parameter regime, which includes all sufficiently strongly stratified flows, where neither of these...
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localisation of coastal Trapped Waves by longshore variations in bottom topography
Computer Science Symposium in Russia, 2012Co-Authors: J T Rodney, E R JohnsonAbstract:Variations in shelf geometry mean that a coastal Trapped Wave mode can propagate within some finite length of shelf but be evanescent outside this region. This paper constructs such geographically localised coastal Trapped Waves using a WKBJ approximation. Comparison with full numerical solutions of the non-linear differential eigenvalue problem demonstrates that the approximation is extremely accurate. The asymptotic and full numerical models are then used to examine the parameters and geometries that govern the existence of these modes.
Dale R. Durran - One of the best experts on this subject based on the ideXlab platform.
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the dissipation of Trapped lee Waves part ii the relative importance of the boundary layer and the stratosphere
Journal of the Atmospheric Sciences, 2016Co-Authors: Matthew O G Hills, Dale R. Durran, Peter N BlosseyAbstract:AbstractDecaying Trapped Waves exert a drag on the large-scale flow. The two most studied mechanisms for such decay are boundary layer dissipation and leakage into the stratosphere. If the Waves dissipate in the boundary layer, they exert a drag near the surface, whereas, if they leak into the stratosphere, the drag is exerted at the level where the Waves dissipate aloft. Although each of these decay mechanisms has been studied in isolation, their relative importance has not been previously assessed.Here, numerical simulations are conducted showing that the relative strength of these two mechanisms depends on the details of the environment supporting the Waves. During actual Trapped-Wave events, the environment often includes elevated inversions and strong winds aloft. Such conditions tend to favor leakage into the stratosphere, although boundary layer dissipation becomes nonnegligible in cases with shorter resonant Wavelengths and higher tropopause heights. In contrast, idealized two-layer profiles with ...
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the dissipation of Trapped lee Waves part i leakage of inviscid Waves into the stratosphere
Journal of the Atmospheric Sciences, 2015Co-Authors: Dale R. Durran, Matthew O G Hills, Peter N BlosseyAbstract:AbstractLeaky Trapped mountain lee Waves are investigated by examining the structure of individual linear modes in multilayer atmospheres. When the static stability and cross-mountain wind speed are constant in the topmost unbounded layer, modes that decay exponentially downstream also grow exponentially with height. This growth with height occurs because packets containing relatively large-amplitude Waves follow ray paths through the stratosphere, placing them above packets entering the stratosphere farther downstream that contain relatively low-amplitude Waves. Nevertheless, if the Trapped Wave train is generated by a compact source, all Waves disappear above some line parallel to the group velocity that passes just above the source region.The rate of downstream decay due to leakage into the stratosphere is strongly dependent on the atmospheric structure. Downstream dissipation is often significant under realistic atmospheric conditions, which typically include elevated inversions and strong upper-tropo...
