Henry Stommel the Scientific Work of Henry Stommel Arnold B

Henry Stommel The Scientific Work of Henry Stommel Arnold B. Arons Tanquam ex ungue leonem. lean Bernoulli, 1697 Henry Stommel graduated from Yale University in 1942 with a major in astronomy and remained at Yale as an instructor in mathematics and astronomy through the wartime years of 1942-1944. In 1944 he took a job with Maurice Ewing, whose group was then located at the Woods Hole Oceanographic Institution. The job, however, initially did not involve full-time residence in Woods Hole. A Coast and Geodetic Survey chart of the Mississippi Delta can still draw Stommel into reminiscences about a period of instrument monitoring at an isolated station in the far reaches of the delta, finger pointing to the location of the remote outpost. On taking up more continuous residence at Woods Hole, Stommel became one of a group of bachelors who formed a kind of informal fraternity residing in the old rectory of the Episcopal church on the east comer of Church Street and Woods Hole Road. All the inmates were members of the Institution staff, and to describe some of them as "characters" would be a form of gentle British understatement. The atmosphere of the rectory, however, was stimulating and congenial and constitutes another source of Stommel's anecdotes and reminiscences. Some of the more senior individuals of this group were quick to grasp the quality of their new young member's intellect. I recall two of them, at that early date, predicting his future leadership in research. Toward the end of World War II, Stommel, becoming interested in the oceans, educated himself in basic oceanography. A by-product of this study was the charming little book Science of the Seven Seas, published in 1945. There followed a period of casting about for lines of research: a note on use of the T-S correla- tion in dynamic height anomaly computations, an ex- ploration of the theory of convection cells, a sally into cloud physics. At one point in this interval he con- sulted Ray Montgomery about outstanding problems in oceanography, and Montgomery pointed to the dy- namically unexplained phenomenon of the Gulf Stream. In 1948 the Transactions of the American Geophys- ical Union carried a short paper entitled, "The West- ward Intensification of Wind-Driven Ocean Currents." This was to become a classic, one of the most frequently cited papers in modem physical oceanography. Some years later I once heard Hans Panofsky say, "That paper? Oh, that's the paper which made Henry Stom- mel famous!" In an elegantly simple model-a plane, rectangular, homogeneous ocean driven by wind torque xiv Arnold B. Arons at the surface and braked by bottom friction-Stommel it illuminating; then with the simplest mathematical showed that the basic dynamical equations predicted methods he extracts the deep and significant physical a flow symmetrical about the central meridian if the insights that hitherto had not been attained. Coriolis term is held constant over the plane but that At this point the most expert applied mathemati- a westward intensification (as in the Gulf Stream) cians take over, usually with Stommel's active en- emerges if the Coriolis term varies linearly with lati- couragement and cooperation, and proceed to extend tude the so-called -effect). and refine the original picture. So it went with the In this day, when the fundamental equations of geo- westward intensification: Munk worked out a more physical hydrodynamics, including variation of the sophisticated model with its multiplicity of "gyres" Coriolis parameter, are casually written down in text and with dissipation provided by a horizontal aus- and lecture presentations for each new generation of tausch coefficient rather than by bottom friction; Mor- students, it is probably difficult for many to grasp the gan and Chamey, in continual personal contact with research atmosphere of a time when the dynamical Stommel, examined the nonlinear aspects; Munk and significance of variation of the Coriolis parameter had Carrier worked out solutions for nonrectangular basins. not yet been fully appreciated by either oceanographers But the deep physical insight opening up the entire or meteorologists. Though it all seems so obvious and field was in the 1948 paper. This paper, as well as the compelling in retrospect, it is well to note that syntheses contained in the 1957 "Survey of Ocean Cur- Bjerknes, Ekman, Defant, Sverdrup, and Rossby had rent Theory" and the 1958 book The Gulf Stream, not perceived the connection with westward intensi- continue to be deeply influential and widely cited. fication in a bounded basin; it was the youthful Henry Stommel has a way of looking at new papers pub- Stommel who did. The 1948 paper coincided with the lished by others, frequently imposingly complex and beginning of a new epoch of research in physical ocean- difficult to penetrate, and, after a relatively short study, ography and constitutes a prototypical example of the stripping away the complexity, revealing the essence Stommel style. of the paper in something of the form and style that he Reference to style calls for explanation of the Latin himself might have used had he formulated the prob- quotation at the head of this essay. In 1696 Leibniz and lem ab initio. His unerring penetration of the essential Jean Bernoulli, striving to demonstrate the power and physical content is steadily guided by his deep, reliable significance of the new mathematical methods of intuition for every aspect of fluid flow. "analysis" (the differential and integral calculus) as During a period in which we were deeply immersed opposed to the ancient methods of "synthesis" (ge- in thinking about Rossby waves, long after Rossby's ometry), posed as a challenge to European mathema- classic paper of 1939, I recall a moment at which Stom- ticians the now well-known brachistochrone problem.* mel emerged from the library where he had been read- They knew that this problem could be solved only by ing Laplace. In a characteristically bubbly way he said, use of the new analytic methods, and they speculated "You know, Laplace's tidal motions of the second class that L'H6pital, James Bernoulli, and Isaac Newton are simply Rossby waves; I hadn't realized this till now." would be among the few likely to meet the challenge. Although we were aware of Haurwitz's 1940 paper in When, early in 1697, Jean Bernoulli saw the correct Journal of Marine Research, in which he had examined and powerful solution published anonymously by the formalism of Rossby waves in spherical coordinates Newton in Philosophical Transactions of the Royal and pointed out their identity with "motions of the Society, he is said to have remarked, "Tanquam ex second class" discussed by Margules, we were not fully ungue leonem"-literally translated, "As from the sensitive to the latter comment. Stommel's insight claw, the lion"; freely translated, "You can tell the lion quite independently penetrated the physical content of by his claw." the arcane Laplace formulation. This is a very fitting metaphor; in Henry Stommel's His depth of intuition sustains another characteristic papers you can almost invariably tell the lion by his that I have frequently seen at play-an almost inartic- claw. He is diffident, almost apologetic, for what he ulate, unswerving sense of when he is on the right regards as his "limited mathematical capacity" in deal- track with some physical idea. When he has this sense, ing with the complexity of oceanographic problems, he will not be deflected, and he will not take his teeth yet in this "limitation" perhaps lies much of his out of a problem. Others will give up and fall by the strength. With consummate artistry he constructs a wayside, but he persists until the initial hunch is model having just the right idealizations to make it brought to fruition. tractable and just the right physical content to make In addition to his profound grasp of dynamics, Stom- mel has a broad descriptive knowledge of oceanic data * To find the curve connecting two points, at different heights and phenomena. If, however, he does not happen to and not in the same vertical line, along which a body acted have something you ask him about at his finger tips, upon only by gravity will fall in the shortest time. he will vanish into the recesses of the library and xv Henry Stommel emerge a little while later with the crucial material in critique of the status of ocean-current theory, it made hand; he knows exactly where it is located. the rounds of the active theoreticians and deeply influ- The range of Stommel's more than 100 publications enced the direction of their thinking. I recall it being embraces not only almost all aspects of physical ocean- referred to repeatedly in seminars and colloquia of that ography (both theoretical and observational) but also period. extends into cloud physics, limnology, and estuarine During the early 1950s, while engaging in a wide circulation. There are observational and theoretical pa- variety of studies ranging from estuarine dynamics, pers on oceanic and limnological thermoclines, on through the monitoring of a long series of temperature time-series observations of thermal "unrest," on the measurements on the bottom off Bermuda, to the use formation and sinking of water cold enough to drop to of submarine cables in measuring potential differences the bottom, on oceanic Rossby waves, on monsoon across oceanic currents, Stommel began to talk more effects in the Indian Ocean, on tidal mixing and density and more explicitly about the need for time-series ob- currents in estuaries, on the Kuroshio, on dynamical servations of pressure, temperature, and current in the transients in the ocean-all containing some illumi- deep ocean.

Load more