Author Archive | fred

The Davidson Current Lives

MPC released its drifter on Nov 14 in Monterey Bay. In the 2.5 months since release, it drifted south, nearly to the latitude of Pt Conception. Then, with the onset of winter storms and the presumable winter-time emergence of the Davidson Current (the slow, northward flowing current that replaces the California Current in the winter months), it has reversed direction and flowed northwards. It now lies farther north than we released it.

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Now *That* got my Students' Attention

To begin my lecture on gyres and surface currents this morning, I showed them this image.

This data, collected by our colleagues at Cape Fear Community College, definitely got their attention. This is especially noteworthy because we’re getting towards the end of the semester where students are dealing with all kinds of assignments and are just trying to survive. A lecture about gyres and the differences between strong and swift western boundary currents and weak and meandering eastern boundary currents that is usually met with bored indifference was suddenly incredibly relevant.

That track was made in two months folks! Heck, I had no idea the Gulf Stream was *that* fast.

Here’s the same data with current SST data behind it.

Does anybody know where I can get a kml file showing higher resolution SST data for the North Atlantic that would show all of the eddies in more detail?

I did find this kml file, but it is from 2005 and the location of the eddies is quite different.

Thanks!

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MPC Drifter Launched Again

We launched the drifter again this past Saturday. This time we set it to transmit every six hours. We’re hoping that it goes out to sea and goes for a long ride. I find myself experiencing drifter envy over the beautifully long and sinuous path the Cape Fear Community College drifter has taken up the Gulf Stream. I don’t have much hope that the California Current will be able to match that ride, so we’ll have to settle with what we get.

Before the cruise I gave my students this image and asked them to predict where the drifter would be in 48 and 96 hours, hoping the challange would give them experience in calculating distances using the rate equation, as well as piquing their interest in following the drifter’s journey.
MBay circulation model with deployment site
 
We purposefully chose a deployment site where it was a tossup whether the drifter would circulate through Monterey Bay or drift out to sea. There wasn’t a right answer. On the assignment, I merely looked to see that the answers were supported by some sort of manipulation of the rate equation.

Here’s the predictions I got from the students. White locations are 2-day forecasts; purple locations are 4-day forecasts.

On the image you can also see where we intended to deploy the drifter–at the MBARI M1 buoy–and where we actually deployed the drifter; we didn’t quite make it to the M1 buoy in our allotted cruise time.

Today in class, the students manipulated the tracking site and Google Earth to show that the 2-day location of the drifter was almost exactly right in between two of the predictions. So we had two winners. So far the drifter has traveled a few miles SW and then turned around and backtracked to the NE.

Here’s a few pictures of the students deploying the drifter.


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A Drifter Lab Exercise

Our Vice president of Academic Affairs asked me the other day if the tsunami affected the motion of the drifters here in Monterey Bay. “Voile!” I thought, what a great idea for a lab. If our vice president thinks that the tsunami might have affected the drifters, then our students must have the same question. So I developed the lab linked below.

I developed the lab to generate interest in the motion of the drifters. My students started on this lab on Monday and will finish it today. What I’m realizing is that perhaps the main benefit will be that in order to understand why the tsunami did not affect the motion of the drifters, the students will have to internalize how waves move about in the ocean, that it is not the flow of water parcels, but rather the water parcels interacting with each other to cause a wave. Ships out at sea are not affected by tsunamis, and neither are our drifters.

A Word format of the lab is available here:
http://www.mpcfaculty.net/alfred_hochstaedter/ocean/lab/DrifterTsunami.doc

 It is also available on the MPC Oceanography website:
http://www.mpcfaculty.net/alfred_hochstaedter/oceanography.htm

-Fred

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Ever Feel Like You’re Just Drifting in Circles


The MPC Drifters are back in the water this week as our MBARI collaboration continues for a second week. The data on the image above represents about 27 hours of data, from the afternoon of October 5 to about 6 pm local time of October 6. It illustrates quite nicely the 24-hour periodicity that is evident in much of our data. We have semi-diurnal tides here on the coast of California, so that pattern is not tidal. The drifters tend to have a stronger SE component of motion in the afternoons and a stronger NW component of motion in the early morning hours.

I’m trying to get some images of students deploying and retrieving the drifters. I’ll post them as soon as I get them.

-Fred

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Serendipity Strikes the Drifter Project

Sometimes it seems like articles in newspapers are published as if they were planned to coincide with my syllabus. This was one such week. We set the drifters adrift on Tuesday and only two days earlier, on Sunday, the New York Times published a piece on surface currents in Monterey Bay, Finding Order in the Apparent Chaos of Currents.

The story has a big flashy graphic that decorated most of the cover of the Sunday Science section of the Times, and comes complete with an accompanying flash video and podcast. Click image for a larger, more readable version.

The article reveals how theoretical scientists are doing some pretty wild stuff with Lagrangian flow models and “Lagrangian coherent structures”. Now, I can barely pronounce “Langrangian”, much less explain it to my students, but there are fascinating revelations in all kinds of fields such as blood flow from ventricles, turbulence in atmospheric flow patterns, and, of course, dispersal of pollutants in the ocean currents.  On this image, the bright colors show the “amount of stretching and chaotic stirring in surface water”. I’m OK with the chaotic stirring, but stretching? Every semester I explain to my oceanography class about the incompressibility of water is the basis of hydraulic brakes working properly. Now I have to explain that water gets stretched somehow? Maybe now that you have taken the time to read this can explain this one to me.

 In any case, the article is very cool, even though I still don’t get a real, physical feel for how water circulates through the bay. It’s a different way of looking at flow with which I have no experience.

 I haven’t decided yet whether to ask my students to read this article. What do you think?

 Drifters come out of the bay today. More on that later.

 -Fred

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The drifters are adrift here in Monterey Bay

Well, the drifters are adrift here in Monterey Bay. They were deployed mid day today, local time by a team from the Monterey Bay Aquarium Research Institute (MBARI) and three Oceanography students from Monterey Peninsula College. The study is part of an intensive effort to look at the physical oceanography associated with harmful algal blooms (HABs) After four messages to the satellite (configured at 48/day), the image looks like this:

 You can see two drifters are out there; the single position is from when the ship was on the way to deployment. Both of the drifters are drifting south or southeast. This is somewhat unexpected as we thought the circulation in Monterey Bay was counterclockwise as I explained in my previous blog.

Wonder why the drifters are drifting southsouthwest? They are moving directly towards the Salinas Valley, probably as a result of seabreezes that pick up every afternoon here. At least that’s my current (ha ha) hypothesis. The winds today are shown on the image above, blowing straight towards the Salinas Valley, which is between Moss Landing and Del Monte Beach on the image above. The drifters were deployed northeast of Moss Landing, somewhat north of the MO buoy as shown on the image above.

 Follow along at the usual spots. I’ll share the response of the students in a later installment.

 Over and out for now,

 -Fred

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Getting Started at Monterey Peninsula College

Greetings from the Central Coast of California. This is my first attempt at blogging, so I hope I do it right. From what I’ve read on other blogs, I think I’m supposed to record my stream of consciousness and try to stay somewhat on topic. We’ll see how that goes.

In an effort to kick-start our drifter program out here on the shores of Monterey Bay, I went and visited Jeff Paduan at the Naval Postgraduate School. Jeff had to put me on a special list just to allow me to walk onto the grounds of NPS. Jeff is the local HF radar guru and has written papers on the circulation of Monterey Bay. Jeff is PI for the Central California component of the Coastal Ocean Currents Monitoring Program, perhaps better known as COCMP. The COCMP website has a nice pdf brochure imaginatively entitled the COCMP Reference Guide (How Ocean Current Mapping Works and How it is Useful) (image at right). It has some nice information that would be useful for teaching students how the HF radar works as well as beautiful color photographs of HF radar antennas in some of the most stunningly picturesque locations in the world. Strangely enough, the best images of Jeff’s HF radar ocean current data are at his Central California Currents page. Here’s what the currents look like for today in our area:

Those circular patterns you see in Monterey Bay on the image on the right are not tidal. They have a 24 hour periodicity and form in response to offshore and onshore breezes that cycle back and forth throughout the day.

Jeff and I talked quite a while about HF radar and I learned quite a bit. I still can’t explain all the intricacies of which frequencies they use to get the best Doppler Effect and why, but at least my eyes won’t roll too far back in my head next time we go through it.

We also talked about “typical” ocean circulation patterns in Monterey Bay. The image below is from one day back in 1994—exaclty 15 years ago from our drifters workshop.

The image shows ocean currents layered over sea surface temperatures. It shows the typical counterclockwise circulation in the bay and the clockwise eddy just outside the bay. As was true on this day in 1994, the northeast portion of the bay is the warmest, and this water is pulled out into deeper water by the currents.

I looked at some of the drifters that Jeff uses in his research. They’re commercially made by Pacific Gyre. They have a floating sphere that contains the transmitter and then a sail system that opens up like an umbrella.

The next stop in my tour of ocean current researchers was the world famous MBARI, the Monterey Bay Aquarium Research Institute, to visit Erich Rienecker and John Ryan. Erich is one of the marine technicians and John is a researcher specializing in phytoplankton blooms. Here’s John and I looking at some eye-popping data on John’s computer. I was just blinking, I swear.

Here’s that eye-popping data John and I were looking at:

The left image shows satellite-generated data for chlorophyll in the water, whereas the right image shows sea surface temperatures. Clearly there are other factors besides just temperatures driving the magnitude of plankton concentrations.

The last week in September and the first week in October, John and Erich will be involved with an intensive data gathering effort in this area involving satellites, AUVs, moorings, and………..drum roll please……… OUR DRIFTERS!

On Monday September 28 and Monday October 2 we’ll send students out on their cruises to deploy our drifters and launch their AUVs among other tasks for this study. Later in the week, we’ll send students out with them to try and retrieve the drifters. Should be fun, and a great experience for the students.

Back in the classroom, we’ll be following the progress of the drifters on the computers. Hopefully this will set the stage for increased interest in learning about atmospheric circulation and ocean currents. Then, in early November, we’ll take the whole class out on a cruise and release one of the drifters once again (assuming all goes well with the MBARI guys).

Over and out,

-Fred

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