Cross-Frontal Exchange and Scotian Shelf Cross-over Workshops

10-12 October, 2000

Holiday Inn, Falmouth, Massachusetts



Cross-Frontal Exchange

Presentations Discussion Topics Upcoming North Sea Study (LIFECO) (St. John)

Scotian Shelf Cross-over

Presentations Discussion Questions Synthesis Topics Appendix


Satellite Observations of the Front

J.J. Bisagni

University of Massachusetts - Dartmouth

1) Literature/historical data show that satellite-derived Sea Surface Temperature (SST) images may be used to delineate regions within the Gulf of Maine (GOM) & Georges Bank (GB) where strong tidal mixing occurs.

  • Construct time series of both satellite-derived SST and the locations of highest SST gradient (fronts) using edge-detection algorithms.

  • Use empirical orthogonal functions (EOF) to examine the signal variance.

  • This mixing must have important physical, chemical, and biological implications for GB.
2) Annual signals dominate the variance for both SST and SST fronts.
  • Areas of high and low annual SST signal amplitude correspond to seasonally-stratified and well-mixed regions on GB, respectively, which are separated by narrow regions of high SST frontal probability, signifying seasonal Tidal Mixing Fronts (TMFs). [see Figure]

  • Long-term, monthly mean, SST frontal probability density function (PDF) maps show that a primary TMF forms on the southern flank of GB during May of each year and moves bankward (into more shallow waters) ~5-km per month during the heating season from June-August. The TMF on the northern flank of GB moves into deeper waters at a somewhat lesser rate over the same period.

  • A secondary TMF forms bankward of the primary TMF by late summer, separating cooler water at the primary TMF from the warm thermostable hot-spot on the crest of GB.

  • Both the primary and secondary TMFs disappear by late fall of each year when the entire GB region becomes well-mixed due to rapid cooling and wind mixing.

  • Both primary and secondary TMFs, along with the shelf/slope front, and SSW cross-overs are captured in an EOF analysis of SST frontal PDF maps.

  • No single isobath, nor Simpson-Hunter depth-dissipation value, log10(h/Dt), may be used to locate the TMF during months when TMFs are present.


Bisagni, J. J., K. W. Seemann and T. P. Mavor, High-resolution satellite-derived sea surface temperature variability over the Gulf of Maine and Georges Bank region, 1993-1996. Deep-Sea Research II (in press).

Mavor, T. P. and J. J. Bisagni, Seasonal variability of sea surface
temperature fronts on Georges Bank. Deep-Sea Research II (in press).