Fall 2005

No seminar this week

Thursday, September 1, 2005

Why is the ocean so skinny?

Dr. Trevor McDougall

CSIRO Division of Oceanography
Hobart, Tasmania, Australia

4:30 p.m., Thursday, September 8, 2005
Note location: KTS Lecture Hall, 2nd floor
New Academic Bldg, King's College

The hydrography of the global ocean is observed to occupy very little volume (and so appears skinny) in salinity-temperature-pressure space; why might this be so?

NOTE: Dr. McDougall is this year's Huntsman Award Recipient for Physical/Chemical Oceanography. He will be receiving the award at BIO on Tuesday Sept 6, and giving a public lecture on his research at BIO on Wednesday Sept 7.

No POMSS This Week

Thursday, September 15, 2005

A Labrador Sea modeling studied by a coupled sea ice-ocean circulation model

Hideaki Kitauchi
Frontier Research Center for Global Change, JAMSTEC
and
Hiroyasu Hasumi
Center for Climate System Research, U of Tokyo

4:30 p.m., Thursday, September 22, 2005

Abstract: Intermediate water formation in the Labrador Sea (Labrador Sea Water, LSW) has a direct connection to the global thermohaline circulation, which influences the long-term global climate. The LSW is formed by means of deep convection, in which eddies are considered to play an important role. We are interested in understanding the roles of eddies on the LSW formation and estimating the formation rate and eddy buoyancy flux by the use of an eddy-resolving coupled sea ice-ocean circulation model.

To this end we compute a basic flow field which is qualitatively consistent with the observed field. The horizontal circulation in the Labrador Sea is simulated well, while the vertical convection needs further improvement. It turns out that the simulated salinity is higher than the observed distribution. This may be caused by the less low salinity flux along the East Greenland Coast, suggesting that the freshwater flux from the Arctic by the East Greenland Current may play an important role for stabilization of stratification in the eastern part of the Labrador Sea by the eddy buoyancy flux.

In the seminar we will present our current status of a Labrador Sea modeling and discuss possible causes of the simulated higher salinity distribution in the Labrador Sea.

No seminar this week

Thursday, September 29, 2005

Heat and Salt budgets under the Peru-Chile Stratus: The role of the mesoscale

Keir Colbo

Woods Hole Oceanographic Institution

4:30 p.m., Thursday, October 6, 2005

Abstract: The persistent stratus clouds found west of Chile and Peru are important for the coupling of the ocean and atmosphere in the eastern Pacific and thus in the climate of the region. The relatively cool sea surface temperatures found west of Peru and northern Chile are believed to play a role in maintaining the stratus clouds over the region. In October 2000 a buoy was deployed at 20S, 85W, a site near the center of the stratus region, in order to examine the variability of the upper ocean and atmospheric boundary layer. The extent to which local forcing explains the temporal evolution of upper ocean structure and heat content was examined. The sources of heating (primarily surface fluxes with weaker contributions from Ekman convergence and transport) are found to be balanced by cooling from the gyre-scale circulation, an eddy flux divergence and vertical diffusion. The deduced eddy flux divergence term is bounded away from zero and represents an order one source of cooling (and freshening). We postulate that the eddy flux divergence represents the effect of the cold coherent eddies formed in the coastal current, which propagate westward and slowly decay. Direct advection of coastal upwelled water by Ekman transport is negligible. Thus the upwelled water does influence the offshore structure, but through the fluctuating mesoscale flow not the mean transport.

No seminar this week

Thursday, October 13, 2005

Interpreting Eddy Fluxes

Richard Greatbatch

Department of Oceanography
Dalhousie University

4:30 p.m., Thursday, October 20, 2005

Abstract:

New Standard for 21st Century Sea Level Prediction in the Upper Bay of Fundy

Charles Hannah

Bedford Institute of Oceanography

4:30 p.m., Thursday, October 27, 2005

Abstract:

The circulation of the Southern Ocean - processes, dynamics and models

Dirk Olbers

Alfred-Wegener-Institut
Bremerhaven, Germany

4:30 p.m., Monday, October 31, 2005
NOTE: Special day

Abstract:

Title

Speaker

Institute

4:30 p.m., Thursday, November 3, 2005

Abstract:

Nonlinear Generation and Loss of Infragravity Wave Energy

Stephen M. Henderson, R.T. Guza, Steve Elgar, T.H.C. Herbers, A.J. Bowen

Scripps Institution of Oceanography

4:30 p.m., Thursday, November 10, 2005

Abstract: Nonlinear energy transfers with sea and swell (frequencies 0.05-0.25 Hz) were responsible for most of the generation and loss of infragravity wave energy (frequencies 0.005-0.05 Hz) observed on a natural beach. Cases with energetic shear waves were excluded and mean currents, a likely shear wave energy source, were neglected. Near the crest of a sandbar, about 70-130 m from the shore, nonlinear interactions usually transfered sea and swell energy to infragravity waves. Within about 40 m of the shore the direction of energy transfer often reversed, so infragravity energy was transferred to sea and swell waves. This nonlinear energy transfer to higher frequencies remains unexplained, although it resembles the breaking-induced energy cascade observed among higher frequency waves by previous researchers. Estimated nonlinear energy transfers roughly balanced gradients in the infragravity energy flux, consistent with a conservative energy equation. Addition of significant dissipation (requiring a bottom drag coefficient exceeding about 0.01) degraded the energy balance.

Funded by the U.S. Office of Naval Research, the National Science Foundation, the Izaak Walton Killam Foundation, the Andrew Mellon Foundation, and NSERC.

CFC simulation in the North Atlantic

Jun Zhao

Department of Oceanography
Dalhousie University

4:30 p.m., Thursday, November 17, 2005

Abstract:

Broadband Acoustic Scattering from Double-Diffusive Microstructure

Tetjana Ross

Department of Oceanography
Dalhousie University

4:30 p.m., Thursday, November 24, 2005

Abstract:

Once again: Once again ADV use in the water column; sound scattering from phytoplankton?

David Ciochetto

Department of Oceanography
Dalhousie University

4:30 p.m., Thursday, December 1, 2005

Abstract: Data were taken with an acoustic Doppler velocimeter (ADV) in the water column in summer 2002 in the Bedford Basin, October 2002 on the Scotian Shelf 30 km from shore, sporadically through 2003 in both locations and in a diatom bloom in a mode water eddy SW of Bermuda in September 2005. In general the data quality were good in Bedford Basin, marginal on the Scotian Shelf and poor in the mode water eddy. This indicated that the shelf is an acoustically hostile environment to the acoustical parameters of the ADV. Two hypotheses for the low quality data have emerged in trying to understand the performance of the ADV in acoustically unfriendly environments. The ADV uses particles to scatter sound from so the basic hypothesis is that there is simply not enough acoustically favorable scattering material present. A competing hypothesis was discovered that in low particle environments, the ADV exhibits a sensitivity to orientation of the transmit axis with respect to the mean flow velocity which may cause poor quality data. The data from Bermuda illustrated that with large (50 um equivalent spherical diameter) diatoms (10% silica shell by volume) failed to scatter sufficient sound to return ample signal strength with any setting or orientation of the ADV.

This talk will focus on a model to help future users of the ADV in suspect acoustically unfriendly environments determine a priori if the instrument is worth using. The model in development is a forward model where the scattering from the particles is assumed to be of the nature of a fluid sphere. This combined with the particle size spectra and assumed biological and background composition of the particles for low particle environments yields a prediction for the volume scattering strength of the targets. Corrections for absorption over the short path of the high frequency acoustic pulse and characteristics of the ADV electronics are applied to predict the amplitude that is expected in the data. Finally the model will be applied to data and particle size spectra measured in Bedford Basin and on the Scotian Shelf.

Title

Speaker

Institute

4:30 p.m., Thursday, December 8, 2005

Title

Speaker

Institute

4:30 p.m., Thursday, December 15, 2005

Check out POMSS after Christmas