Coastal trapped waves

The intra-annual response of the Black Sea main pycnocline to the annual forcing by momentum and vorticity fluxes from the wind is manifested in the superposition of two principal modes a basin-scale standing oscillation and sub-basin hybrid Rossby-coastal trapped waves, which form quasigeostrophic cyclonic amphidromic systems. 

Coastal Trapped Waves and Continental Shelf Waves... 

When the shelf scale is comparable with the internal Rossby radius, wave motions normal to the shelf induce vertical motions due to the inclined bottom that generate internal pressure gradients. Therefore, a separation between barotropic and baroclinic modes is not possible anymore and these modes are denoted as mixed or hybrid modes that have been called coastally trapped waves. To evaluate their dispersion relations with respect to frequency and longshore wave number and their modal structure in the vertical plain normal to the coast, a two-dimensional eigenvalue problem must be solved numerically (Brink, 1991). The nodal lines of the velocity modes of these hybrid modes are inclined with respect to the sea surface in contrast to the baroclinic modes in case of a flat-bottomed ocean. 

Brink, K. H., 1991. Coastal-trapped waves and wind-driven currents overthe continental shelf Annual Review of Fluid Mechanics, 23, 389-410. 

Huthnance, J. M., 1978. On coastal trapped waves analysis and numerical calculation by inverse iteration. Journal of Physical Oceanography, 8, 74-92. 

It is illuminating to study the time evolution of a river plume as an initial value problem. It can be shown that the current pattern is governed by a geostrophically adjusted eddy confined to the buoyancy patch (near field) and a coastally trapped flow that develops in the wake of a Kelvin wave (far field). Behind the front of the first Kelvin wave mode, undercurrents are set up. Although the velocities of the flow forced by the momenrnm of the river mnoff are small enough to justify a linear treatment, there are important nonlinear effects owing to the advection of density, which limits the validity of the linear analytical models. In particular, the structure of the near field in front of the river mouth is dominated by the response to the buoyancy flux associated with the river discharge. 

Liquid water, including its soluble and insoluble constituents, is transferred from the oceans to the atmosphere when air bubbles in the water rise to the surface. These bubbles form from air trapped by breaking waves, "whitecaps." As the bubbles burst at the surface, water droplets are injected into the atmosphere. These water droplets are small enough to remain airborne for several hours. Whitecaps begin to form in winds common over the oceans, and a significant amount of seasalt made airborne in this way is transported to the continents and deposited in coastal areas. 

The arbitrary longshore shape of the wave described by G x — ci) remains unchanged while propagating along the coast and can be of a localized or a sinusoidal pattern. The Kelvin wave is trapped in a coastal wave guide along the coast and is not felt offshore of this guide with the width determined by the Rossby radius. Barotropic Kelvin waves have a wide Rossby radius of the order of = 0(100 km) and baroclinic waves a Rossby radius of the order of R = 0(5 km) in the Baltic Sea. 

Nonstructural erosion-control methods in coastal environments can be modeled after natural features such as coastal-dune environments or saltwater marshes to create buffers that absorb the enei of waves or storm suites. These approaches include limiting access for foot and vehicle traffic in areas vulnerable to erosion and revegetating wdth native plants. The plants trap wdnd-bome sediment and sand and anchor coastal soils wdth their root systems. Revegetation measures may include the use of geotextiles or mulches to protect the soil surface while the vegetation becomes established. 

The most valued part of a coastline is often the sandy beach. Sand is washed into the ocean as the result of weathering of silicon-rich quartz and feldspar rocks upstream and distributed along the shoreline by the action of ocean currents and waves. Human intervention has reduced the amount of sand available. Dams built on streams trap sand as sediment, depriving the ocean of its source of sand. Improper beach management can result in loss of beach sand. The term littoral cell applies to a region of shoreline that includes inflow of sand from a stream or from seacliff erosion, transport of sand generally parallel to the coast by ocean currents and wave action, and eventual loss of sand from the coastal region. 

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