Winter/Spring 2004

Happy New Year!

Thursday, January 1, 2004

A View From "The Other Side"

Todd Mudge
Principal Oceanographer

SonTek/YSI Inc.
San Diego, CA

4:30 p.m., Thursday, January 8, 2004




Department of Oceanography
Dalhousie University

4:30 p.m., Thursday, January 15, 2004


Differential mixing of heat and salt

Barry Ruddick and Ann Gargett

Department of Oceanography
Dalhousie University

Old Dominion University

4:30 p.m., Thursday, January 22, 2004


Physical Limnology of Okanagan Lake

Ryan Mulligan

Department of Oceanography
Dalhousie University

4:30 p.m., Thursday, January 29, 2004


"Deep jets in the equatorial Atlantic Ocean

Carsten Eden

Institut fur Meereskunde Kiel

4:30 p.m., Thursday, February 5, 2004

Abstract: Using general circulation models of the tropical Atlantic (part of the FLAME hierarchy of models) with very high vertical resolution, we are able to simulate Atlantic equatorial deep jets, with spatial and temporal structures similar to observational estimates. The vertical wave length of the stacked jets are adequately resolved, such we are able to exclude possible numerical artifacts, apparently present in model version with lower vertical resolution.

Inertial instability of the deep zonal currents set by their (inertially unstable) vertical and meridional shears near the equator is proposed as one of the possible generation mechanism for the deep jets. In the model simulation, we find the necessary condition for this instability to occur (Ertel potential vorticity times the Coriolis parameter less than zero), surprisingly often fulfilled in the deep equatorial Atlantic, such that it appears possible that the jets might be be generated by this mechanism.

No seminar this week

February 12, 2004

Blizzard Day - No seminar this week

February 19, 2004

3D coupled physical-biological modelling the North Atlantic

Svetlana Loza, A. Vezina, D. Wright, K. Thompson, Y. Lu, and M. Dowd

Department of Oceanography
Dalhousie University

4:30 p.m., Thursday, February 26, 2004


Bay of Fundy Tides - Past Present Future

David Greenberg

Bedford Institute of Oceanography

4:30 p.m., Thursday, March 4, 2004

Abstract: The claimed "highest tides in the world" dominate the ocean characteristics of the Bay of Fundy. An examination is made of the factors giving rise to these tides and some of the fun oceanography associated with them.

Mechanical energy input and dissipation to the wind-driven circulation

David Straub

McGill University

4:30 p.m., Thursday, March 11, 2004

Abstract: Traditional models of wind-driven circulation have that energy input by the winds is ultimately dissipated in association lateral or bottom friction term. At high Reynolds number (i.e., in an eddy-resolving regime), the lack of a forward energy cascade in geostrophic turbulence suggests that lateral dissipation of energy should be negligible, leaving the overall balance as one between wind power input and dissipation by bottom friction. This traditional view is challenged on two fronts. First, it is argued that a weak dependence of wind stress on the surface ocean velocity field can lead to a relatively large reduction in the wind input. Basic scaling arguments and results from model simulations are presented to support this claim. A second point is that a significant sink could result from energy transfers out of the "balanced" modes of flow and into forward-cascading unbalanced modes (such as the gravity wave field). These transfers can occun either over rough topography or in regions where local measures of the Rossby number are O(1). We concentrate on the latter, and argue that such transfers are both generic and well-described by hydrostatic dynamics.

No seminar this week

Thursday, March 18, 2004

No seminar this week

Thursday, March 25, 2004

THE MOLECULAR POOL TABLE: a new paradigm for computational fluid dynamics?

Lorenzo S. F. de la Fuente

Department of Oceanography
Dalhousie University

4:30 p.m., Thursday, April 1, 2004

Abstract: The lattice Boltzmann (LB) method is a powerful new technique for simulating fluid flows based on discrete lattice models. It is briefly introduced, and described relative to traditional finite-difference (FD) methods. Afterwards its performance in three reference flow regimes is demonstrated. Practical modelling considerations for atmospheric applications are discussed, including FD/LB implementation differences and computational costs. Oceanic LB applications are examined, and a list of relevant papers concludes the talk.

High wavenumber bed elevation fluctuations in nearshore sands: Spectra, slope distribution functions, and dissipation

Alex Hay
Department of Oceanography
Dalhousie University


Anna Crawford
Defense Research and Development Canada - Atlantic

4:30 p.m., Thursday, April 8, 2004

Abstract: Bed elevation spectra, bed slope spectra and bed slope probability distribution functions are determined from laser-video imaging measurements in the nearshore zone during a storm event, for three different bed states: vortex ripples, cross ripples and linear transition ripples. At spatial frequencies above the ripple band (i.e. above 0.3 cm-1), the bed elevation spectra exhibit k-3/2 dependence on wavenumber k below a critical wavenumber k/2π = 1 cm-1, and a slope-doubled k-3 dependence above. The bed slope spectra peak at the critical wavenumber. Based on a conservation equation for bed elevation fluctuation variance derived from rough surface growth theory, the slope spectrum is shown to be proportional to the spectrum for the dissipation of elevation fluctuation intensity, and the critical wavenumber likely to be related to the thickness of the mobile layer within which most of the dissipation must occur. The slope distributions peak at negative angles (shoreward slopes) and are skewed toward positive angles (seaward slopes), consistent with seaward bedform migration and negative wave orbital velocity skewness in the overlying fluid. The asymmetries in the slope distribution functions are reproduced in synthetic bed profiles constructed from a Fourier series expansion, provided that the high wavenumber constituents are phase-locked, indicating that the dynamics governing the fluctuations are non-linear.

No seminar this week

Thursday, April 15, 2004

Water Mass Formation South-West of Tasmania

Paul Barker

Acadia University

4:30 p.m., Thursday, April 22, 2004


Tracers for Climate Studies in the High-Latitude Seas

Kumiko Azetsu-Scott

Department of Fisheries and Oceans
Bedford Institute of Oceanography

4:30 p.m., Thursday, April 29, 2004


No seminar this week

Thursday, May 6, 2004

No seminar this week

Thursday, May 13, 2004

No seminar this week

Thursday, May 20, 2004

A Laterally-Averaged Nonhydrostatic Ocean Model

Daniel Bourgault

Dept. of Physics and Physical Oceanography
Memorial University of Newfoundland

4:30 p.m., Tuesday, May 25, 2004

Abstract: I will present a laterally-averaged model that we (Dan Kelley and I) have developed for the simulation of nonhydrostatic phenomena, such as high-frequency internal waves, in dynamically-narrow domains. Averaging laterally the equations of motions yields the computational efficiency of a 2D model, while retaining some effects associated with variable domain width, such as flow acceleration through constricting channels. I will illustrate the strengths and weaknesses of this approach with a series of test cases and will provide examples of problems that have been tackled with this tool.

No seminar

Thursday, May 27, 2004

No seminar

Thursday, June 3, 2004

A model study of bipolar oscillations of the thermohaline circulation driven by orbital forcing

Gus Fanning

St. John's, NL
Candidate for Research Associate position

11:00 a.m., June 8, 2004

Abstract: An idealised geometry coupled climate system model is utilized to investigate millenial timescale variability due to changes in solar radiative forcing on orbital timescales. Beginning from 224 kyr bp the model is integrated forward in time to the present. Modeled high latitude ice growth and decay is found to be predominantly driven by precessional changes and to a lesser extent by changes in obliquity.

In step with this variability are large changes in the thermohaline circulation and hence poleward heat transport. Results suggest that the changes in ice volume are driven not only by in-situ changes in insolation, but also by the advection of heat via the thermohaline circulation from mid-latitudes. Finally the model suggests evidance of Broecker's bipolar seesaw hypothesis in which the strength of the thermohaline circulation oscillates between hemispheres with anomalies in one being perfectly reflected within the other.

No seminar

Thursday, June 10, 2004

Karman-Benard vortex streets in two-dimensional wakes

V. Korabel

Memorial University of Newfoundland
St. John's, NL

10:30 a.m., June 15, 2004

Abstract: Two-dimensional wakes behind localized forcing in a uniform stream are investigated using direct numerical simulations and asymptotic theory. The behavior if frequency of vortex shedding in the unstable wakes is described in detail for different values of the main control parameters of the flow, namely the amplitude of the forcing area and kinematic viscosity of the fluid. Asymptotic relations are obtained for two distinct regimes of the flow. Theoretical solutions for the wake generated by the localized forcing allows us to obtain a relation which describes the boundary between the two regimes in the parameter space.

Development of a Limited Area Variational Analysis System at the Meteorological Service of Canada

Luc Fillon

Meteorological Service of Canada
Dorval, Quebec

11:00 a.m., June 16, 2004

Refractions of surface gravity waves by surf zone currents

Steve Henderson

Scripps Institution of Oceanography

4:30 p.m., July 22, 2004