baroclinic tides off the se us coast h. seim, c. edwards, t. shay – unc chapel hill c. werner –...
TRANSCRIPT
![Page 1: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/1.jpg)
Baroclinic Tides off the SE US Coast
H. Seim, C. Edwards, T. Shay – UNC Chapel HillC. Werner – now at Rutgers University
• Some background
• Shelf observations
• SAB – generation site considerations
![Page 2: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/2.jpg)
Munk&Wunsch,DSR, 1998
![Page 3: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/3.jpg)
Estimate of kinetic energy dissipated from M2 tide
Egbert&Ray, GRL, 2003
![Page 4: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/4.jpg)
Barotropic tidal analysis reveals seasonal cycle to tide – why?
Blanton et al, 2004
M2 tide at Ft. Pulaski, GA
![Page 5: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/5.jpg)
SC
GA
NC
FL
Study area: South Atlantic Bight – shallow (<50m), up to 100 km wide, bounded by Gulf Stream
R4
![Page 6: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/6.jpg)
R4M2 Majoraxis
M2 Minoraxis
Repeatable seasonal variations apparent in tidal current analysis
m/s m/s
40
![Page 7: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/7.jpg)
![Page 8: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/8.jpg)
R2 R6
Stations further from shelfbreak show less variability in vertical structure – but analysis captures only phase-locked component of the tide
0.4 0.36
25 30
![Page 9: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/9.jpg)
To examine baroclinic tide in shallow water, need to remove the barotropic tide, including its associated vertical structure due to bottom friction.
Use EOF analysis to define vertical modes. Associate first mode with barotropic dynamics, sum of higher modes with baroclinic (Edwards and Seim, 2008).
1st mode=barotropicdynamics
![Page 10: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/10.jpg)
Apr-Jul05Jul-Nov05Dec-Feb06Feb-Jun06
Internal current variability –different vertical structure at diurnal and semi-diurnal frequencies
Diurnalvariance
Semi-diurnalvariance
![Page 11: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/11.jpg)
Seasonal SD baroclinic variance (m2/s2)
40 m isobath
32misobath
25 mIsobath(why larger?)
![Page 12: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/12.jpg)
R8
R4
Near shelfbreak magnitudes vary on weekly time scale
m/s
![Page 13: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/13.jpg)
More obvious seasonal variability at mid-shelf
![Page 14: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/14.jpg)
Glider-obs at R4 - SD pycnocline motion - 2-5 m amplitude. More nonlinear at max tide range. N2 profile suggests 40 cm/s speedphase speed.
m/s
Depth-averaged current
Temp (C)
![Page 15: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/15.jpg)
Observations summary
• Semi-diurnal tidal current varies seasonally• Baroclinic tide (defined via EOF) of 5-10 cm/s
apparent on mid-outer shelf• Vertical structure dominated by mode 1• Magnitude varies on weekly time scales on outer
shelf, on seasonal time scales at mid-shelf• Consistent with offshore generation and onshore
propagation of an internal tide
![Page 16: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/16.jpg)
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
![Page 17: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/17.jpg)
Tidal ellipses for the SAB – good potential for generation at shelfbreak
Blanton et al., 2004
![Page 18: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/18.jpg)
SC
GA
NC
FL
Presence of the Gulf Stream:
Impacts density structureover shelfbreak
Modifies the effectiveCoriolis parameter
Together with varyingtopography, may leadto large changes in generated internal tide
![Page 19: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/19.jpg)
Wintertime chlorophyll image
Nelson, SkIO
![Page 20: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/20.jpg)
![Page 21: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/21.jpg)
Changes in stratification overslope can focus or defocus waveenergy
![Page 22: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/22.jpg)
Critical angle - when the angle ofwave propagation matchesthe bottom slope can getenhanced responseand wave beam typestructure.
![Page 23: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/23.jpg)
Quoddy model runs, nested in basin scale model (Alfredo/Tom/Cisco)
![Page 24: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/24.jpg)
Mean temperature structure – shoals over the slope
![Page 25: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/25.jpg)
Critical angle – how best assessed? Looks like a match in places
Slope angle
Waveangle
![Page 26: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/26.jpg)
Cross-shore velocity variance – see some maxima near areas of criticalslope – generation sites?
![Page 27: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/27.jpg)
Measuring the mass field
Pycnocline position varies at the semi-diurnal; current structure dominated by the diurnal
Glider-measured density near R4
![Page 28: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/28.jpg)
Can begin to look at cross-shore variability…from inshore (GR)
![Page 29: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/29.jpg)
Across to shelfbreak (R4)
![Page 30: Baroclinic Tides off the SE US Coast H. Seim, C. Edwards, T. Shay – UNC Chapel Hill C. Werner – now at Rutgers University Some background Shelf observations](https://reader035.vdocument.in/reader035/viewer/2022081514/56649c785503460f9492d181/html5/thumbnails/30.jpg)
Bandpassed sum of higher modes -
u
v
w