J.J. Bisagni

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.

• 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.

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