internal tides seim, edwards, shay, werner some background sab – generation site? shelf...
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Internal tidesSeim, Edwards, Shay, Werner
• Some background
• SAB – generation site?
• Shelf observations
• Towards a climatology?
Munk&Wunsch,DSR, 1998
Estimate of kinetic energy dissipated from M2 tide
Egbert&Ray, GRL, 2003
Extract energy from barotropictide where flow pushes stratifiedfluid over topography
Vlasenko et al.,2005
Amplitude of response dependson:Height and width of obstacleStratification strength and depthFrequency of forcing
Critical angle - when the angle ofwave propagation matchesthe bottom slope can getenhanced responseand wave beam typestructure.
Tidal beam on the CA slope andassociated mixing
Waves can be greatly modified after generation via nonlinearities, transform intoWave packets (aka solitons or solibores)
SC
GA
NC
FL
Wilmington
Jackson-ville
Savannah
Charleston
Our study area – SAB
Big complicatio
n – Gulf Stream
Changes in stratification overslope can focus or defocus waveenergy
Other fun piece – Brian Blanton’s work – annual variation in tidal amplitude – why?
Quoddy model runs, nested in basin scale model (Alfredo/Tom/Cisco)
Mean temperature structure – shoals over the slope
Critical angle – how best assessed? Looks like a match in places
Slope angle
Waveangle
Cross-shore velocity variance – see some maxima near areas of criticalslope – generation sites?
SC
GA
NC
FL
Onshore side – have several years of ADCP(current meter) data – any sign on internal tide?
Challenge – tides dominatevelocity variance and shelfso shallow that boundarylayer influences structurethroughout – how to isolateinternal waves?
Describing internal structure in shallow water
Goal: To remove the barotropic tide, including its associated vertical structure due to bottom friction
Method: EOF analysis
Isolates internal structure within energetic barotropic dynamics
Done by: Catherine Edwards
Non-mode0 bandpassed data – lots of info…
Apr-Jul05Jul-Nov05Dec-Feb06Feb-Jun06
Internal current variability – dominated by diurnal (near inertial) but has different structure than semi-diurnal currents (bottom-trapped?)
Measuring the mass field
Pycnocline position varies at the semi-diurnal; current structure dominated by the diurnal
Glider-measured density near R4
Can begin to look at cross-shore variability…from inshore (GR)
Across to shelfbreak (R4)
Towards a summary – time and cross –shore – mode 1
And mode2
In conclusion…
Internal tides – exist in the SAB but not as highly NL form?
Generation – likely on slope but quite variable
Shelf obs – can isolate internal structure, beginning to look at variations x-shelf and with time.