Part ThreeTechniques ofInvestigationI4Ocean Instrumentsand ExperimentDesignD. ames Baker, Jr.What wonderful andmanifest conditions ofnatural power haveescaped observation.[M. Faraday, 1859.]We know what gear willcatch but ... we do notknow what it will notcatch.[M. R. Clarke (1977).]14.1 Observations and the Impact of NewInstruments"I was never able to make a fact my own withoutseeing it, and the descriptions of the best works alto-gether failed to convey to my mind such a knowledgeof things as to allow myself to form a judgment uponthem. It was so with new things." So wrote MichaelFaraday in 1860 (quoted in Williams, 1965, p. 27) closeto the end of his remarkably productive career as anexperimental physicist. Faraday's words convey to usthe immediacy of observation-the need to see naturalforces at work. W. H. Watson remarked a century lateron the philosophy of physics, "How often do experi-mental discoveries in science impress us with the largeareas of terra incognita in our pictures of nature! Weimagine nothing going on, because we have no clue tosuspect it. Our representations have a basic physicalinnocence, until imagination coupled with technicalingenuity discloses how dull we were" [Watson (1963)].Faraday recognized the importance of this couplingwhen he wrote in his laboratory Diary (1859; quotedin Williams, 1965, p. 467), "Let the imagination go,guiding it by judgment and principle, but holding it inand directing it by experiment."In the turbulent, multiscale geophysical systems ofinterest to oceanographers, the need for observationand experiment is clear. Our aim is to understand thefluid dynamics of these geophysical systems. Althoughgeophysical fluid dynamics is a subject that can bedescribed with relatively few equations of motion andconservation, as Feynman, Leighton, and Sands (1964)stated, "That we have written an equation does notremove from the flow of fluids its charm or mystery orits surprise." In fact, observations and experimentshave been crucial to the untangling of the mysteries offluid processes in the ocean and in the atmosphere.For example, on the smaller scales, lengths of theorder of tens of meters and less, the discovery of thesharp discontinuities in density, temperature, and sa-linity that was brought to focus by the new profilinginstrumentation has given us a whole new picture ofmixing in the ocean. On the large scale, a good exampleis the explanation of the general circulation of theatmosphere in terms of baroclinic instability. The the-oretical development was firmly based on the remark-able set of observations of the atmosphere carried outin the 1940s and 1950s. As E. Lorenz (1967, p. 26) notedin his treatise on The Nature and Theory of the Gen-eral Circulation of the Atmosphere, "The study of thecirculation owes a great deal to the practice of weatherforecasting, for without these observations our under-standing could not have approached its present level.Yet certain gaps will continue to exist in our knowl-edge of the circulation as long as extensive regions396D. James Baker, Jr.---·-L---_.--l - _---· ____, I-· -- -- -, __ _ _without regular observations remain." The emphasisthat Lorenz placed on the need for observations beforeunderstanding can occur is equally valid for oceano-graphic studies of the same scale.One must search long and hard for counterexampleswhere theory has preceded observation in geophysics.One of the few such examples in oceanography is theprediction and subsequent confirmation by directmeasurement of southward flow under the Gulf Streamby the Stommel-Arons theory of abyssal circulation.The theory is discussed elsewhere (e.g., chapters 1 and5, this volume) so I shall not pursue it further. Thepoint is that observations guide and appear to limit theprogress of our science. There is no inherent reasonthat this should be so. Why is our imagination so lim-ited that, as Watson put it, we are so dull? Perhaps thehistorian of science can answer the question.If observations guide the science, then new instru-ments are the means for guidance. The following twoexamples show how this has occurred; we considerfirst the North Atlantic circulation. Most of our ideasabout the ocean circulation have been based on theindirect evidence of the temperature and salinity fieldsand the assumption of geostrophy. With the advent ofdirect velocity measurements by deep floats and-cur-rent meters during the 1960s and early 1970s, the nec-essary data for a consistent picture of ocean circulation,at least in limited areas, began to come in. Worthing-ton's (1976) attempt to put together for the first timesuch a picture of circulation in the North Atlantic wasbased on the new direct data.One of the important pieces of evidence used in thework by Worthington were the data from the neutrallybuoyant floats, which show a high transport for theGulf Stream [see Worthington (1976) for references].Until the direct measurements, the distribution of theabsolute velocity field was ambiguous. With the newdata, Worthington was encouraged to put together acomplete picture that includes a tight recirculationpattern. However, within the constraints he used, Wor-thington's attempts at a complete mass and dynamicbalance for the entire North Atlantic circulation werenot successful. He decided, therefore, to choose a cir-culation pattern that was not consistent with geostro-phy. This provocative work stimulated a number ofattempts to look more closely at the circulation systemthere. Because both scale analysis of the equations ofmotion and the direct moored measurements ofSchmitz (1977, 1980) confirm geostrophy to the leadingorder, as do the measurements reported by Swallow(1977) and Byrden (1977) in the MODE region of theSargasso Sea, Worthington's total picture is not correct.The moored data are consistent with the recirculationpattern, but, in addition, reveal a flow with an eastwardcomponent immediately south of the Gulf Stream andnorth of the recirculation. The latter feature is notclearly contained in any existing picture of the NorthAtlantic circulation.A second approach was taken by Wunsch (1978a),who used hydrographic data, mass balance, and geos-trophy to estimate
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