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The last boat afloat

Though most of our friends have left, the science crew of the Sally Ride has been enjoying our final few days of surveying.   Some of the topics that have been on our mind this week include wakes associated with flow around topography, strong fronts created by confluence in these wakes, or by confluences in the generally eddying along-shore flow, and how any of that structured momentum and buoyancy variance is ultimately dissipated.

Here are a few examples. First we have a composite of 24 hours of repeat occupations of an “L” pattern near Pt Sal.   The flow (black arrows) not only changes significantly over a tidal cycle, but shows a variety of small-scale eddies to boot.  Bow chain temperature (color) shows a wealth of features, including trains of incoming solitary waves as well as sharp fronts likely associated with the topographic wakes. This was from the same time period we had ALL SEVEN (!) large and small boats operating in the vicinity, and we are very excited to work with everyone to fill out this map.

 

 

A zoom in on one front near Pt Sal shows it to be incredibly sharp, only a couple meters wide at most (top panel) with elevated turbulence on one side of the front (middle panel), and complex turbulent structures visible in biosonics (lowest panel). [courtesy Ata Suanda, Anna Savage, Sean Haney].

Many of these very sharp, strong fronts were also observed with the GusT probes on our bow chain, with high resolution turbulence data remarkably matched to the sharp gradients, suggestive of any number of interesting instabilities [Alexis Kaminski and Jim Moum]

We get a slightly different view of our ocean full of fronts from the air.  The SIO and UW aircraft of course have been giving us excellent birds eye views of all manner of features.  Closer in, an IR camera on a quadcopter shows us a variety of very complex looking frontal structures (image a few hundred meters wide, courtesy of Eric Lo and Amy Waterhouse)

 

Inspired by some of these interesting features all of the boats observed near Pt Sal, we more recently spent a day and a half sampling near Pt. Purisima, where we observed another strongly eddying flow (details forthcoming). On a roll, and benefiting from the high winds currently blowing us home not being as difficult as expected, we conducted one final compare-and-contrast topographic survey near Pt. Arguello.

Finally, we took some time to conduct several high resolution cross-shore surveys (at Pt. Sal, Pt. Purisima, and Pt. Arguello), which may provide some insight into incident flow characteristics and boundary/validation conditions for our regional modelers.

We’re a few hours out of port, so more from the other side.  Nice working with you all!

 

 

 

 

Tidal variability of headland eddy shedding

 

The Sally Ride and Oceanus are both wrapping up long (36-48 hour) repeat sections down here at Pt. Sal before heading back to Oceano. Following up on the Sounder post below, we have also been intrigued by the strongly time-dependent nature of the wake eddies being shed south of Pt. Sal.

The figure above shows 15 passes around our “L” shaped Sally Ride pattern, with local time given at the top. Color is SST and arrows are depth-averaged currents.

During and following periods of strongly southward (tidal+mean) flow, e.g. the second and third panels, an energetic recirculation eddy results on the onshore end, consistent with small boat measurements reported below. Related (somehow!) to these recirculations, there is a frequently occurring clear front (red to blue colors).  At times it seems clear that the sharpness of this front is related to convergences between separated southward flow and recirculation eddies, for example in panel 13. At other times, the structure and location of both the density fronts and the current patterns seem a tad mysterious.

We can only imagine that once we collectively integrate measurements from all seven ships! (3 big, 3 small) plus drifters!  into this pattern, the nature of the flow will either be even more mind-blowingily confusing, or magically crystal clear. So much fun analysis to look forward to.

 

 

 

Tidal Bore and Soliton tracking on Oceano

Sally Ride is tracking tidal bores and internal solitary waves (ISWs) on the Oceano array today and through the night on a small southern box between the 20 and 50m isobaths. Our box coordinates are

SRSW 34 58.241,  120 44.448

SRSE   34 57.912,  120 41.031

SRNE   34 58.795,  120 40.086

SRNW 34 59.211,  120 44.251

 

After a tumultuous night of lightening and rain we were greeted by an inspiring sun rise.

 

Our survey instrumentation includes a CTD bow chain down to 20-m depth, a bow mounted IR camera and radiometer, a pole mounted 500 kHz ADCP, 120 and 200 kHz echo sounders, and a vertical microstructure profiler (VMP).

The observations are revealing interesting internal structure of the ISWs, as seen by the echo sounders.

[Caption: Internal Bolus? Colliding ISWs? Biological Scatter?]

Also, significant lateral small-scale variability of the waves is seen by this opposing and following cross section of an ISW wave train. The opposing and following transects are separated by 100-200m along the wave crest.

 

The waves appear to be coming from both the WNW and WSW and are traveling at an average speed of 25 to 30 cm/s. VMP and Bow chain results forth coming!

 

 

 

Mooring madness on the Sally Ride

The R/V Sally Ride arrived on site Friday morning local time and got right to work.  We had initially laid out what we thought was a slightly conservative but reasonable schedule of mooring deployments that would last for the first 4.5 days of our expedition.  We had not counted on the incredible energy, talent, precision and hard work of all of our mooring teams.  Friday we deployed 13 moorings, including the two large NRL ‘quad-pods’, and today another 17!  After two days of hard work we now have all but the final 5 deployed. Instead of being done mid-day on Tuesday, we now expect to have completed all mooring deployments by mid-day Sunday.  This will allow us to switch to process-based survey mode full time, joining our colleagues on the Oceanus, Sproul, Kalipi, and Sounder in coordinated sampling. We’ve been practicing our survey techniques on the night watch; more on some of those preliminary results tomorrow.  In the meantime, a few photos of our team hard at work.

scripps oceanography uc san diego