Mr. Tom's Blog

polyMODE

Immediately following the very successful Mid-Ocean Dynamics Experiment (MODE) discussions developed between the MODE leadership and oceanographers at the Shirshov Institute of Oceanology in Moscow, USSR about a possible joint study. They had recently completed a somewhat similar study in the eastern Atlantic called POLYGON. To explore this, Prof. Allan Robinson at Harvard, Dr. Bill Schmitz at WHOI, and I at Yale were invited to Moscow that fall (1973) for initial discussions and planning for what became known at polyMODE. I was the junior member of the group and included, I think, because the Shirshov people were very interested in our Lagrangian approach to studying oceanic motion using SOFAR floats. But, in fact, almost all planning pivoted around where to site polyMODE, the details of current meter array, and the hydrographic surveys.

There was quite a lot of travel between the USSR and the US from that point on. Much of it focused on planning for the field program, but there were also several scientific workshops that were highly appreciated. The planning for the field work was challenging, the biggest concern being the siting and design of the current meter moorings. The current meters they used were rather primitive. The data from the rotor and the vane were printed out like on cash register paper. The paper roll limitation (perhaps the battery too?) required that each current meter had to be retrieved on a monthly schedule. They were evidently comfortable with this having acquired considerable experience from their earlier POLYGON study. The other and more serious concern was that they planned to use surface flotation for the moorings. Bob Heimerdinger at WHOI argued strenuously that their moorings must not have any surface expression. By then it had been well-established that the heaving motions of the surface flotation would be communicated down the wire inducing an unwanted motion of the current meter leading to exaggerated estimates of speed. The solution was to use subs-surface flotation and acoustic releases to bring the mooring to the surface. I think they understood the issue but didn’t have the resources to buy releases from outside the USSR (and allegedly couldn’t be manufactured in the USSR). Bob made this point over and over again, and our Soviet colleagues replied that if this is so important you buy them for us. I stopped traveling to Moscow since there was little I could contribute.

Much of the final decision-making was probably in Allan’s and Prof. Andrei Monin’s hands (the director of the Shirshov Institute). I say this mainly from the observation that any agreements we might make with their technical staff had to go up the ladder to Monin and back ‘down’ the scientific side of the institute for review before he would approve. Even if we all did agree on something, it still had to be approved by the director, there seemed to be very little if any delegation of authority. Something like this, it was all very awkward. They centered their array of 19 moorings at 29°N 70°W while our array of 10 moorings was centered at 31°N 69°30’W. Their moorings had current meters at 100, 400, 700, and 1400 m depth and were serviced on a monthly schedule from August 1977 through August 1978.

Then there was the question of sharing the data afterwards. A detailed agreement can probably be found in an archive somewhere. In any event, a delegation came in November 1980, first to URI, and then to Harvard for the purpose of sharing data and starting the analyses. The three people who came were excellent scientists and data analysts, and very professional about their work. They were also very good ping-pong players. Imagine our surprise when they said they would only release current meter data from the 700 and 1400 m levels but excluding the temperature data. They did share more data at Harvard so looking back it may have been intended as a match to the two float levels we operated at. We gave them our SOFAR float trajectory data. But after brief discussion we decided to delete the temperature data from the trajectories. Seems kind of petty but that is what we did.

Arthur Mariano, a young graduate student with us at the time, and Chris Polloni worked together to produce a series of objectively mapped stream functions from the current meter data, in much the same way Howard Freeland and John Gould had prepared the stream function fields in MODE. It was in this work the sad truth came to light. A number of SOFAR floats had passed very close to some of their moorings. This allowed us to compare float velocity to recorded current meter velocity. Chris and Arthur made a plot of these comparisons, and they correlated well. Good news for it validated the methodology, but sadly the current meter speeds were all high by a factor 1.75±0.4. Fortunately, the directions agreed quite well. I think the Harvard group worked out methods to address this shortcoming in their subsequent analyses.

All these challenges notwithstanding the SOFAR float trajectories gave us a wealth of information about thermocline and deep ocean currents.. I’ll try to recap some of these learnings from over 40 years ago shortly.


Polloni, C., A. Mariano and H.T. Rossby. Stream function Maps of the Soviet POLYMODE Current Meter Array. Technical Report, April 1981.