Winter/Spring 2003
Transport of suspended sediment on a natural beach
Stephen Henderson
College of Oceanic and Atmospheric Sciences
Oregon State University
4:45 p.m., Thursday, January 9, 2003
Note Special Time
Abstract:
Transport of suspended sediment under waves is predicted by coupling an
eddy-diffusive numerical model for sediment suspension with a
one-dimensional numerical wave boundary layer model. Predictions of beach
erosion and accretion, calculated from the divergence (or convergence) of
the simulated depth-integrated suspended sediment flux, are compared with
the observed erosion and accretion of a natural beach. The effects of
gravity and bedload transport on beach change are not simulated. A single
free parameter, which determines the rate of sediment pick-up from the
seabed, is adjusted to calibrate the model. The calibrated model predicts
much of the observed beach profile change, including both the seaward
sandbar migration which occurred during a storm, and the shoreward sandbar
migration which occurred between two storms. A simplified, analytic model
for transport of suspended sediment under waves is derived. Predictions
of transport obtained using this simplified model are compared with
numerical predictions, and with the observed beach change.
No seminar this week
Thursday, January 16, 2003
Measurement of fluvial bedload transport using an acoustic Doppler current
profiler
Colin Rennie
Department of Oceanography
Dalhousie University
4:30 p.m., Thursday, January 23, 2003
Abstract:
Observations from a moored profiled ADV on the Scotian Shelf
David Ciochetto
Department of Oceanography
Dalhousie University
4:30 p.m., Thursday, January 30, 2003
Abstract: A Nortek Vector ADV was incorporated with a SeaHorse Moored
Profiler and the Epsmapper turbulence probe. The instrument package
was tested in the Bedford Basin during the summer of 2002 and deployed
on the shelf during October 2002. Problems with the data and
instrument performance were hinted at in the data. A presentation of
the work on this data will be presented and discussed. This is still a
work in progress so comments and discussion are greatly appreciated.
Naval applications of the acoustical ocean
Dan Hutt
Ocean Sensing and Modelling Group
Defence R&D Canada - Atlantic
4:30 p.m., Thursday, February 6, 2003
Abstract:
Modern navies rely on underwater acoustics for communication,
reconnaissance and detection but these capabilities are limited by
the ocean environment. One of the main constraints is imposed by the
thermal structure of the ocean which controls acoustical propagation.
Also, there are fundamental trade-offs between range, spatial
resolution and temporal resolution. Finally, the state of the ocean
surface affects underwater acoustics through the contribution of
ambient noise and the effect of interface scattering. The issues
affecting naval applications of underwater acoustics will be reviewed
and relevant research at DRDC Atlantic will be presented.
No seminar this week
Thursday, February 13, 2003
No seminar this week
Thursday, February 20, 2003
No seminar this week
Thursday, February 27, 2003
Wave-Current Bedforms on Sable Island Bank
Carolyn Smyth
Bedford Institute of Oceanography
4:30 p.m., Thursday, March 6, 2003
Abstract:
Southern Ocean Iron Fertilization Experiment (SOFeX)
Ken Johnson
Monterey Bay Aquarium Research Institute (MBARI)
4:00 p.m., Thursday, March 13, 2003
Location: LSC4263 (Psychology Wing)
NOTE SPECIAL TIME AND LOCATION!
Abstract:
A method for adiabatically adjusting ocean models
Richard Greatbatch
Dalhousie University
4:30 p.m., Thursday, March 20, 2003
Abstract:
A new and exciting technique, known as the semi-prognostic
method, is described. The method can be used to correct models for
systematic error, e,g, poor Gulf Stream separation and poor representation
of the Northwest Corner, and uses hydrographic data as input. The method
is adiabatic, meaning that it does not rely on introducing diabatic sources
and sinks. Rather, the idea is to use hydrographic data to introduce
forcing terms into the model momentum equations. The method is easy to
implement, computationally very cheap, and has application beyond
that to be described here. In particular, it can be used a method for
transferring information between the different subcomponents of a nested
modelling system. The method is illustrated using a regional model of the
Northwest Atlantic as well as an eddy-permitting model of the entire
North Atlantic. Some comparisons are shown with a 1/12 deg eddy-resolving
model of the North Atlantic.
Tracing Arctic Ocean Near-Surface Waters
Peter Jones
Bedford Institute of Oceanography
4:30 p.m., Thursday, March 27, 2003
Abstract:
A Numerical Study of Tidal circulation in Lunenburg Bay
Jinyu Sheng and Liang Wang
Dalhousie University
4:30 p.m., Thursday, April 3, 2003
Abstract:
On the role of air-sea fluxes in extra-tropical hurricanes
Will Perrie
Bedford Institute of Oceanography
4:30 p.m., Thursday, April 10, 2003
Abstract:
Calculating the Flow Around Ships
David Hally
DRDC Atlantic
4:30 p.m., Thursday, April 17, 2003
Abstract: The first attempts to calculate the flow of the water around a ship
were undertaken well over 100 years ago. However, it is only in the
last decade that accurate flow predictions have been possible. This
seminar will describe the features typical of ship flows, why DRDC
Atlantic is interested in calculating them, the methods we use to
calculate them, and topics that we are still researching.
Interannual variability of meridional transports
in the Atlantic: a model intercomparison
Jens-Olaf Beismann, C.W. Boening, D. Stammer (and the FLAME group)
Institut fuer Meereskunde an ber Universitaet Kiel
Germany
4:30 p.m., Thursday, April 24, 2003
Abstract:
Three different medium-resolution ocean models
(based on MOM, OPA, and the MIT codes)
are used to study the response of the meridional
overturning circulation to interannual
to decadal atmospheric variability associated with
the NAO. The emphasis is on the identification of
robust elements in the simulations as well as on the
differences caused by different numerical
representations of physical processes. The simulations
are analyzed with respect to spatial patterns and
time scales of oceanic transport fluctuations. Using
sensitivity experiments with a higher resolution (1/3
degree) version of one of the models we investigate
the relation between low-frequency variations of
meridional transports in the North Atlantic and
transport indices derived from hydrographic time
series. Furthermore, we study the pathways and
mechanisms by which dynamical and passive tracer
anomalies originating from fluctuations in deep water
formation propagate southward.
No seminar this week
Thursday, May 1, 2003
SPECIAL SEMINAR:
Breakup of the stratospheric polar vortices
Pingping Rong
Earth & Planetary Sci., Johns Hopkins University
4:30 p.m., Thursday, June 26, 2003
Abstract:
The temperature in the Earth's stratosphere (between 12 to 50 km)
increases with altitude due to ultraviolet heating of ozone. A strong
circumpolar flow, called the stratospheric polar vortex, forms during
polar winter when ultraviolet heating ceases in this region. These
polar vortices last until spring and then break up as ultraviolet
heating returns. The structure and evolution of the polar vortices
have significant implications on ozone depletion and on global and
regional climates.
40 years of meteorological analyses are used to
examine the evolution of, and stirring around, the Arctic vortex,
with focus on the breakup stage. Two extreme regimes of vortex
breakup are found, late and early breakups, with very different decay
characteristics. The occurrence of these different breakups is
closely related to the interannual variability of the forcing due to
the upward propagating planetary waves.
A shallow water model is used to examine the basic processes
responsible for the different observed regimes. This model includes
topographic forcing, to represent the upward propagating waves, and
relaxation to an equilibrium state, to represent radiative
processes. The roles of, and competition between, topographic wave
forcing and radiative relaxation are examined by systematically
varying the different parameters. Both steady and vacillation states
are produced, which may be related to cold and warm polar
stratospheres, respectively. Calculations with an annual cycle for
the radiative equilibrium state and different timing and seasonality
of the bottom forcing are also performed to produce the observed
breakup regimes.
A new hybrid numerical method which includes diabatic forcing and can
resolve steep gradients is also tested and used to further examine
the competition between the external forcing and radiative
relaxation. Calculations of idealized planar flows show that the
relaxation damps out the oscillations in the elongation as well as
orientation of a forced vortex, but steep vorticity gradients are
preserved for at least 10 vortex overturning periods.
SPECIAL SEMINAR:
Volcanic Eruptions and Climate: Winter Warming and Summer Cooling
Alan Robock
Department of Environmental Sciences
Rutgers University
11:00 a.m., Tuesday, July 29, 2003
Abstract:
Large volcanic eruptions inject sulfur gases into the
stratosphere, which convert to sulfate aerosols with an e-folding
residence time of about one year. Large ash particles fall out much
quicker. The radiative and chemical effects of this aerosol cloud
produce responses in the climate system. Using examples from major
eruptions of the past and results from experiments with numerical models
of the climate system, this talk illustrates the major impacts. One of
the most interesting is the "winter warming" of Northern Hemisphere
continents following major tropical eruptions. During the winter in the
Northern Hemisphere following every large tropical eruption of the past
century, surface air temperatures over North America, Europe, and East
Asia were warmer than normal, while they were colder over Greenland and
the Middle East. This pattern and the coincident atmospheric
circulation correspond to the positive phase of the Arctic Oscillation.
Using the Max Planck Institute ECHAM4 and the Geophysical Fluid Dynamics
Laboratory SKYHI GCMs, we have successfully simulated this response
following the 1991 Mount Pinatubo eruption. In spite of the decrease in
surface solar heating, surface air temperature increases in high and
midlatitudes of the Northern Hemisphere in the winter because of changes
in tropospheric circulation caused by stratosphere-troposphere dynamical
coupling and volcanically-induced ozone depletion. The phase of the
Quasi-Biennial Oscillation also affects the dynamical response.
The June 15, 1991 Mount Pinatubo eruption was a large but
relatively short-lived shock to the climate system. It thus provided an
excellent opportunity to study its workings, to test climate models, and
to examine the impacts of climate change on life. When forced with
observed aerosols, the Geophysical Fluid Dynamics Laboratory (GFDL) R30
climate model reproduces the observed cooling and drying of the
atmosphere for several years after the Pinatubo eruption. By comparing
model simulations with and without water vapor feedback, we demonstrate
the importance of the atmospheric drying in amplifying the temperature
change, and show that without the strong positive feedback from water
vapor the model is unable to reproduce the observed cooling. These
results provide quantitative evidence of the reliability of water vapor
feedback in current climate models. This confirmation of climate model
physics and sensitivity, combined with our other work on climate system
dynamics and connections between stratospheric and tropospheric
circulation, give strong validation to the models used for attribution
and projection of anthropogenic effects on climate.
SPECIAL SEMINAR:
Recent developments in shallow sea/shelf edge modelling
Alan Davies
Proudman Oceanographic Laboratory, UK
11:00 a.m., Tuesday, August 19, 2003
Abstract:
A brief overview of the development of a three dimensional baroclinic
shelf edge model will be presented with its subsequent application
to the study of internal tides. The nature of wind forced flow in
the region and the importance of the resonant non-linear coupling
between near inertial internal waves and the internal tide producing
energy at the M2 frequency will be examined. The importance of
internal wave-wave interaction upon mixing at the shelf edge and its
implications for ocean circulation models will be briefly discussed.
Trappping of wind induced near-inertial internal waves by along
shelf flows and frontal jets, and the implications for enhanced local
turbulent mixing will be illustrated.
The role of internal tides, stratification and wind waves in
determining sediment resuspension at the shelf edge will be
presented.