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Bibliography of the Maurice Lamontagne Institute

Zhigang XU

XU, Z., 2007. The all-source green's function and its applications to tsunami problems. Sci. Tsunami Hazards, 26(1) : 59-69 .

The classical Green’s function provides the global linear response to impulse forcing at a particular source location. It is a type of one-source-all-receiver Green’s function. This paper presents a new type of Green’s function, referred to as the all-source-one-receiver, or for short the all-source Green’s function (ASGF), in which the solution at a point of interest (POI) can be written in terms of global forcing without requiring the solution at other locations. The ASGF is particularly applicable to tsunami problems. The response to forcing anywhere in the global ocean can be determined within a few seconds on an ordinary personal computer or on a web server. The ASGF also brings in two new types of tsunami charts, one for the arrival time and the second for the gain, without assuming the location of the epicenter or reversibility of the tsunami travel path. Thus it provides a useful tool for tsunami hazard preparedness and to rapidly calculate the real-time responses at selected POIs for a tsunami generated anywhere in the world’s oceans.©2007 The Tsunami Society

XU, Z., J.W. LODER, 2004. Data Assimilation and Horizontal Structure of the Barotropic Diurnal Tides on the Newfoundland and Southern Labrador Shelves. Atmos.-Ocean, 42: 43-60 .

A large set of in situ currents and elevation data, and a direct inverse data assimilation model are used in conjunction with global inverse tidal solutions to obtain high-resolution regional assimilative model solutions for the barotropic K1 and O1 tides on the southern Labrador and Newfoundland Shelves. The regional model assimilates the in situ data and a first estimate of the boundary conditions provided by the global model, so that the regional solutions draw on both regional and larger-scale observations and dynamics. The regional assimilative solutions have r.m.s. observational misfit values of the order of 2 cm for elevation and 2 cm s-1 for currents, which are reduced (compared with non-assimilative regional solutions) by 21 % and 61 % for K1 and O1 elevations respectively, and by 61 % and 54 % for K1 and O1 currents. A striking feature of the regional model solutions is a series of small-scale (radius of approximately 100 km) eddy-like features along the shelf edge. Singular value decomposition (SVD) of the assimilative elevation fields reveals the existence of topographicallytrapped waves at the shelf edge. There are amplified diurnal currents over the outer shelf and slope associated with the topographic waves, pointing to the potential for topographic amplification of other subinertial currents in the region.©2004 Canadian Meteorological and Oceanographic Society

WRIGHT, D.G., Z. XU, 2004. Double Kelvin Waves over the Newfoundland Shelf-break. Atmos.-Ocean, 42: 101-111 .

Xu and Loder (2004) present results from a data assimilative model for the diurnal tides over the Grand Banks and the southern Labrador Shelf. Their results include small-scale spatial structures that are not resolved by the data, leaving some question about their validity. The fact that these eddy-like features occur along the shelf-break, upstream of a sudden widening of the slope region, leads us to speculate that they may be double Kelvin waves generated when coastally trapped waves propagating along the shelf encounter the abrupt change in topography. Here, we examine the free wave modes that exist at the diurnal frequency to determine if the allowable modes support this conjecture. We find that the double Kelvin wave does exist at the diurnal frequency and that 85 % or more of the variability along a line through the area of interest can be accounted for by a linear combination of the first mode continental shelf wave and the double Kelvin wave. These results suggest that this conjecture is very likely the correct interpretation of the numerical model results. Previous theoretical investigations of double Kelvin waves in a homogeneous fluid are reviewed within a common framework.©2004 Canadian Meteorological and Oceanographic Society