1,721,161 research outputs found
Notes on a 1-D model of continental shelf resonances
Full text linkThis paper reviews earlier work and provides new results from a one-dimensional model of the scattering of a tidal wave by a continental shelf. When the continental shelf is many wavelengths wide, a large fraction of the incident tidal energy can propagate from the deep ocean onto the shelf. In contrast when there is a nearby coastline most of the energy is reflected unless the shelf approximately 1/4, 3/4, 5/4 etc wavelengths wide and has a suitable amount of frictional damping. The properties of the reflection coefficient are investigated. It is shown that it can be treated as a function of complex angular velocity, strong absorption of tidal energy being associated with nearby poles in the complex angular velocity plane. Physically the poles correspond to decaying shelf modes, their real component depending primarily on the geometry of the region and their imaginary components to their rate of decay. The latter depends on both the bottom friction, acting on the shelf, and on the radiation of energy back into the deep ocean. It is also shown that the reflected wave can be zero when the two are equal and that this can occur for physically realistic values for the depths, shelf width and bottom friction coefficient. Shelf resonances thus provide a classic example of impedance matching. The amplitude and phase of the reflected wave are also investigated and it is found that when plotted in a suitable manner as a function of real angular velocity they produce a characteristic loop as each resonance is passed. Such loops can be be useful for identifying nearby resonances in model studies and in data from the real ocean
On the impact of a radiational open boundary condition on continental shelf resonances
Full text linkStudies carried out with a one-dimensional model of a continental shelf and deep ocean have shown that the use of a radiational boundary condition doubles the decay rate of the shelf resonances. This note reports on a study using a model of the English Channel and Irish Sea which shows that, in this more realistic model, a radiational boundary condition based on Flather (1976) has a much smaller effect
On the adjoint of Laplace’s tidal equations
Full text linkThe concept of the adjoint is regularly used in studies of both the resonances of physical systems and their response to external forcing. This report reviews the underlying theory involved in the adjoints of both differential equations and matrices and shows how the theory may be used to derive a physically meaningful adjoint to Laplace’s Tidal Equations.
Numerical models of the tides usually use a finite difference form of the tidal equations. The report investigates the adjoint properties of the finite difference equations. It shows that the are not necessarily symmetrical, i.e. the finite difference form of the adjoint tidal equations may not be the same as the adjoint of the normal finite difference equations. It also shows that, with a suitable choice of the way the boundary conditions and Coriolis terms are represented, the finite difference forms can be made symmetric
A comparison of sea surface temperatures in the Equatorial Pacific Nino regions with results from two early runs of the NEMO 1/12° Ocean Model
Full text linkSea surface temperature observations from the Nino regions of the Tropical Pacific are compared with results from two 1/12° runs of the NEMO global ocean model. The results show good agreement between the model and observations.There was some concern that the model surface temperatures were being strongly coupled to the actual temperatures via the surface boundary conditions. The near surface structure of the ocean was investigated, as were the individual surface flux terms, but no evidence of strong coupling was found. In fact during the strongest warming periods the surface boundary conditions cooled the ocean more than normal
RRS Charles Darwin Cruise 34A, 15 August - 30 September 1988. Near surface physical oceanography and meteorology of the western equatorial Pacific
Full text linkOn the shelf resonances of the Gulf of Carpentaria and the Arafura Sea
Full text linkA numerical model is used to investigate the resonances of the Gulf of Carpentaria and the Arafura Sea, and the additional insights that come from extending the analysis into the complex angular velocity plane. When the model is forced at the shelf edge with physically realistic real values of the angular velocity, the response functions at points within the region show maxima and other behaviour which imply that resonances are involved but provide little additional information. The study is then extended to complex angular velocities, and the results then show a clear pattern of gravity wave and Rossby wave like resonances. The properties of the resonances are investigated and used to reinterpret the response at real values of angular velocity. It is found that in some regions the response is dominated by modes trapped between the shelf edge and the coast or between opposing coastlines. In other regions the resonances show cooperative behaviour, possibly indicating the importance of other physical processes
On the shelf resonances of the English Channel and Irish Sea
Full text linkThe resonances of the English Channel and Irish Sea are investigated using the methods of Webb (2012a) together with an Arakawa C-grid model of the region under study. In the semi-diurnal tidal band, the high tides of the Bristol Channel and Gulf of St. Malo are shown to be due to two shelf resonances which strongly couple the two regions. In the diurnal band, the response is complicated by the presence of continental shelf waves
- …
