The Generation of Long Shelf Waves by the Wind

Gill, A. E.; Schumann, E. H.

doi:10.1175/1520-0485(1974)004<0083:tgolsw>2.0.co;2

Cited by 272 publications

(151 citation statements)

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“…The free response decreases in coherence and amplitude with distance offshore and away from its upshelf source, much like a classic CTW (Gill and Schumann, 1974). It is observed at all frequencies, but the relative contribution of non-local energy to the SSP signal is greatest at frequencies where the stress is weak.…”

Section: Discussionmentioning

confidence: 99%

Subtidal response of the Scotian shelf bottom pressure field to meteorological forcing

Schwing

1989

Atmosphere-Ocean

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Section: Discussionmentioning

confidence: 99%

Subtidal response of the Scotian shelf bottom pressure field to meteorological forcing

Schwing

1989

Atmosphere-Ocean

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“…The assume that the alongshore length scale is much greater than the offshore scale and thereby salvage the vital simplifications afforded by the boundary layer approximation. This approach has been successfully used by Gill and Schumann (1974) and Csanady (1978) and will be employed here as well.…”

Section: ---------mentioning

confidence: 99%

The dynamics and kinematics of the coastal boundary layer off Long Island

Pettigrew¹

1980

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Data from the COBOLT experiment, which investigated the first 12 km off Long Island's south shore, are analyzed and discussed. Moored current meter records indicate that the nearshore flow field is strongly polarized in the alongshore direction and its fluctuations are well correlated with local meteorological forcing. Complex empirical orthogonal function analysis suggests that subtidal velocity fluctuations are barotropic in nature and are strongly influenced by bottom friction.Wind-related inertial currents were observed within the coastal boundary layer (CBL) under favorable meteorolgical and hydrographical conditions. The magnitude of these oscillations increases with distance from shore, and they display a very clear 180 0 phase difference between surface and bottom layers. Nearshore inertial oscillations of both velocity and salinity records appear to lead those further s€award, suggesting local generation and subsequent radiation away from the coast.The response of the coastal zone to impulsive wind forcing is discussed using simple slab and two-layer models, and the behavior of the nearshore current field examined. The major features of the observed inertial motions are in good qualitative agreement with model predictions. It is found that, in a homogeneous domain, the coastal boundary condition effectively prohibits inertial currents over the entire coastal zone. In the presence of stratification the offshore extent of this prohibition is greatly reduced and significant inertial currents may OCcur within one or two internal deformation radii of the coast. The "coastal effect", in the form of surface and interfacial waves which propagate -3-away from the coast, modifies the "pure" i nerti al response as it would exist far from shore. The kinematics of this process is such that a 180· phase difference between currents in the two layers is characteristic of the entire coastal zone even before the internal wave has had time to traverse the CBL. It is also suggested that, for positions seaward of several internal deformation radii, interference between the surface and internal components of the coastal response will cause maximum inertial amplitudes to occur for t > x/c2, where c2 is the phase speed of the internal disturbance.The hydrographic structure of the CBL is observed to undergo freQuent homogenization. These events are related to both advective and mixing processes. Horizontal and vertical exchange coefficients are estimated from the data, and subsequently used in a diffusive model which accurately reproduces the observed mean density distribution in the nearshore zone.Dynamic balance calculations are performed which indicate that the subtidal cross-shore momentum balance is very nearly geostrophic. The calculations also suggest that the longshore balance may be reasonably represented by a steady, linear equation of motion which includes surface and bottom stresses.Evidence is presented which shows that variations in the longshore wind-stress component are primarily responsible for the ener...

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“…Consequently, the Ekman number used by Allen (1978, 1983) in their calculations (E~/2 = 0.06) must be multiplied by the relative depth change across the shelf to get E l / 2 . For the example parameters used.in Table 3 Periodic wind forcing along a coast is expected to radiate free waves of all modes at the forcing frequency (Gill and Schumann, 1974). The lowest modes are generally the most readily excited suggesting that the energy propagating in mode 1 should dominat~that of higher modes.…”

Section: Discussionmentioning

confidence: 99%

“…The FOWE method was first proposed by Gill and Clarke (1974) and Gill and Schumann (1974) and has since been generalized by Clarke (19na), Brink and Allen (1978), Brink (1982a) and Clarke and Van Gorder (1986). If only low frequencies (periods in the range several days to a few weeks) are considered, and it can be assumed that alongshelf variations in the currents occur over distances much greater than the shelf width, then the propagation of a set of CTWs is governed by a set of coupled first-order wave equations.…”

Section: Introductionmentioning

confidence: 99%

Scattering of coastal-trapped waves by irregularities in coastline and topography

Wilkin¹

1988

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A study is conducted of the scattering of freely-propagating subinertial frequency coastaltrapped waves (CTWS) by large variations in coastline and topography using analytical and numerical techniques. Particular attention is paid to the role of stratification because, as shown, the introduction of even modest stratification can eliminate backscattered free-waves with large wavenumbers which occur, theoretically, in a barotropic ocean.An analytical solution is presented for the scattering of barotropic waves incident upon a discontinuity in shelf width. Discussion of solutions relying on backscattered free-waves is avoided by considering only the range of parameters over which energy transmission is nearly 100%. The solution shows there is a substantial transfer of energy to modes other than that of the incident wave. The transmitted mode most readily excited is that which has the acrossshelf structure most closely coinciding with that of the incident wave. For a widening shelf, energy is therefore readily transferred to higher modes. The resultant presence of multiple modes produces a strong modulation in flow intensity and phase progression downstream of the scattering region which may affect the iaterpretation of shelf wave observations. A nondispersive shelf wave 'pulse' of limited a10ngshelf extent scatters iato a train of similarly shaped waves of all allowable modes, each propagatiag at its own free-wave speed.To overcome limitations of the analytical study a numerical model which accomodates arbitrary density stratification, bathymetry, and coastline, is employed. Numerical simulations are conducted of the scattering of CTWs by a set of topographic and coastline variations which are representative of many continental shelves. The strength of the scattering observed is found to be proportional to a topographic warp factor which estimates the severity of the topographic irregularities. The scattering is amplified by density stratification. A comparison of the effects of widening and narrowing topographies shows that the gross scattering effects of 'reciprocal' topographies are qnite similar. Within the scattering region itself, the strengths of the scattered-wave-induced currents exhibit substantial variation over short spatial scales. On both widening and narrowiag shelves, there is generally a marked intensification of the flow within the scattering region, and significant differences in the directions of the currents at points separated by a few tens of kilometers indicate the occurence of rapid variations ia phase. On narrowing shelves, the influence of the scattering can extend upstream into the region of 1 2 uniform topography even when no freely-propagating backscattered waves exist.A simulation is condncted of CTW scattering at a site on the East Coast of Australia where observations suggest the presence of scattered freely-propagating CTWs. The success of the model simulation in reproducing features of observations confirms that realistic shelf geometries can scatter significant levels of ...

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The Generation of Long Shelf Waves by the Wind

Cited by 272 publications

References 0 publications

Subtidal response of the Scotian shelf bottom pressure field to meteorological forcing

Subtidal response of the Scotian shelf bottom pressure field to meteorological forcing

The dynamics and kinematics of the coastal boundary layer off Long Island

Scattering of coastal-trapped waves by irregularities in coastline and topography

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