Surface currents from AVHRR image sequences

The vectors plotted above show surface velocity computed from AVHRR imagery by the method of Maximum Cross Correlations for a 2-day period centered on May 18, 2006.

The MCC surface velocities show strong flow of warm water into the big warm core ring due south of Cape Cod. The flow appears to diverge and pass either side of the feature. Flow is consistently southwestward in the shelf/slope front throughout the Mid-Atlantic Bight, and also southwestward further offshore over much of the Slope Sea.

The MCC method objectively tracks the displacement of small scale anomalies in sequential infrared imagery, and composites these after a series of consistency and significance checks (Bowen et al., 2002). Here we use all possible AVHRR channel-4 image pairs separated by 3 to 13 hours. Where vectors are absent there were insufficient clear image pairs or statistically significant displacement estimates to derive a useful current vector. These results were computed from imagery acquired by the HRPT receiver at IMCS, Rutgers University (courtesy of Jen Bosch), with MCC processing by Ian Crocker at the University of Colorado. This MCC analysis is experimental but shows promise in this test as a tool for visualizing surface current trajectories through much of the MAB shelf and slope.

Reference:

Bowen, M., W. J. Emery, J. Wilkin, P. Tildesley, I. Barton and R. Knewtson (2002), Extracting multi-year surface currents from sequential thermal imagery using the Maximum Cross Correlation technique, Journal of Atmospheric and Oceanic Technology, 19, 1665-1676.

Endurance Line Glider Transect

May 21: The big warm core ring near 69.5W continues to be shaved off by the Gulf Stream meander, further reducing its size to that of a normal ring. That small warm eddy at the shelf break near 72.W west persists.

A glider has been sent in. The map at the top shows its about half way there.

Origins of the Great Red Spot of the Slope Sea

May 13: First clue to formation. The tail end of the warm water pulse shooting south
along the shelf slope front appears to be pulling water off the shelf behind the trailing edge.



May 16: Earliest satellite image of the red spot at 73 W, 39.5 N

The Scream

May 18: An artists rendition of the Gulf Stream. The big eddy continues to be trimmed back in size. But whats that little red spot at 72W, 39.5N thats spinning in the clockwise direction? Its pulling some cold shelf water around itself. We'll have to go back into the individual images to see where that came from. We still have a band of warm water along the New Jersey shelf break. Coldest water from the Gulf of Maine region looks to be flowing south at midshelf.

Another Week in the life of the Big Eddy

May 14: A study in solid body rotation.

May 11: A good day for an ring-meander interaction. I seem to be getting smaller.

More Shots of the Great Warm RIng of 2006

Thought I would check around to see who else is picking up this big warm ring. Here is a picture from the Navy altimeter product. I always go to NRL first for altimetry. No warm core rings in the slope sea are anywhere near the height of the Great Warm Ring. The color scale of red to blue looks like a full meter of sea surface height. So its spinning with top speeds near 2 m/sec.

Warm Water at the Shelf Break Shoots South

May 10: Here's the longest range Codar map of the day. The jet at the shelf break is still heading south around 50 cm/sec.



May 10: Clouds are clearing in the southern half of the Mid-Atlantic Bight.
Tonight's imagery shows that the warm water from the Gulf Stream Ring continues to head rapidly south along the shelf break, and now extends south to the Chesapeake Bay.

Notes: The surface data is pretty amazing. The biggest warm core ring I've ever seen, followed by this significant transport along the entire shelf break nearly to Hatteras. Maybe it will reach there by tomorrow, and be entrained back in the Gulf Stream. Just taking the long way to Europe. George Forristall and I had a drifter that did something like that once back in 1983 or 4. The big question that keeps coming up is what does the subsurface look like in that shelf-slope jet. The Rutgers COOL group prepped an underwater glider today to find out. It just returned from the LaTTE Hudson River Plume experiment after being deployed and recovered by the Oceanus. We added a little more weight today for the extra salinity we'll encounter, and we'll deploy it tomorrow from Tuckerton before the storm hits thursday night or friday. It will take us a few days to fly it out there, but I think we'll get their in time to find out how these gliders can operate in the strong currents we see out there. We'll also see how deep that thing is.

Outer Shelf Region Awash

May 9: After the clear days over the weekend, clouds set in, winds picked up and so did the waves. Increases in wave height increase the range of the CODAR coverage. This one shows the strong currents in the shelf break front meandering their way down the shelf, likely leaving the out shelf region awash in warm water from the Great Warm Ring. Current velocities in the jet are running about 50 cm/sec.

The Shelf-Slope Jet Takes Over

May 5: The Great Warm Ring still extends fully across the slope water, from the Gulf Stream the shelf break. The warm water on the northeast side is heading down the shelf break front along the entire New Jersey shelf break. The surface shelf slope front is displaced significanly shoreward of the shelf break. There is a lot of hot water heading south fast. On the northern side, cold shelf water is being pulled off and transported clear across the slope and along the Gulf Stream north wall.

3 Degrees of Shelf Interaction

April 28: Most of the Great Warm RIng is visibile today. Its is interacting with the shelf break between 69W and 72 W. Warm water is starting to be pulled off and is headling to the west along the shelfbreak.

First Full Shot of the Great Warm Ring

April 25, 2006: This is the biggest warm core ring I have ever seen. I remember a similar great ring back in 1988 or 1989, but that one was long and narrow, and it broke up into three pieces. This one is nearly circular. It extends completely across the shelf from the Gulf Stream near 68W to the Shelf Break near 71W. Remember that warm water on the northeast side. Its a little farther north now and right up against the shelf break.

The Great Warm Ring is Born

April 20: The ring forms. Note the warm water streaming off the northwest quadrant.

Formation of the 5 Degree Meander

April 14: Thats one big eddy thats about to pinch off. The meander extends from 66W to 71W.

A Circular Meander Shape

April 3: Large meander crest is starting to close at its base. The older warm ring to the east is being absorbed.

Meander Creast Interacts with Older Rings

March 30: The meander crest grows rapidly to the north. The warm patch that was directly north has been absorbed. The creast is interacting with an older warm ring on its eastern side.

The Set Up - Initial Deepening of the Trough

March 17: The Meander Trough has deepened, the upstream crest propagates to the east, and the downstream crest stalls but grows. Classic cold core ring formation.

Meandering Gulf Stream

March 11: A typical meandering Gulf Stream before the start of the Great Warm Core Ring formation. The trough near 69W is going to deepen rapidly over the next several days. Maybe its interacting with a cold core ring to the south. Also, check out the warm water to the north of the crest just downstream of the trough.