Johan Sandström

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Johan Sandström was a Swedish oceanographer.

In 1908 he conducted the series of classical experiments at Bornö oceanographic station in Sweden. His experiments concerned themselves with the causes of ocean currents, particularly those found in fjords. Sandstrom was principally concerned with the role of heating and cooling in driving such currents, and in the larger-scale circulation in general.

Sandstrom asserted that thermal circulation can cause vigorous, steady circulation only if heating occurs at greater depths than cooling. This is known today as Sandström's theorem. Referring to it as such, however, is clearly incorrect, as molecular diffusion can in fact lead to circulations driven by heating and cooling where the heating and cooling are at the same level but offset in the horizontal (Park and Whitehead, 2000) or even when the heating is above the cooling (Coman et al., 2006). Sandström's key (though not clearly expressed) insight, was that in such circulations, the circulation as a whole must transport light water downwards and dense water upwards. This means that the effect of the circulation is to increase the potential energy. Such an increase requires an external source of energy. Recent work has built on this to argue that the ocean circulation as a whole is driven by these external sources of energy, whether wind or tides, with newer work suggesting that internal sources and sinks of energy (such as those driving diffusion) are also potentially important.

[edit] References

Coman, M.A., R.W Griffiths, and G.O. Hughes,Sandström's experiments revisited, Journal of Marine Research, Volume 64, Number 6, November 2006, pp. 783-796.