Johan Sandström
Encyclopedia
Johan Wilhelm Sandström (also referred to as J. W.), born 6 juni 1874 in Norra Degerfors, Västerbotten County
, died 1947, was a Swedish
oceanographer.
He is most famously known for conducting a series of classical experiments at Bornö
oceanographic station in Sweden
that were reported in Sandstrom (1908). 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 ocean 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. Sandstrom's theorem represents an attempt at extending the well known result of classical thermodynamic theory that in order for a heat engine to perform positive work over a cycle, the work of expansion needs to occur at greater pressure than the work of contraction. Sandstrom's theorem is therefore technically true, as long as expansion in the fluid is caused by heating and contraction by cooling, and that greater depths occur at greater pressures. There is an ambiguity, however, as to the meaning of the terms 'heating' and 'cooling' in Sandstrom's theorem. So far, heating and cooling has always been interpreted in the literature as being associated with 'surface heating' and 'surface cooling' respectively. In real fluids, however, molecular and turbulent diffusion always cause internal heating/cooling even in absence of external heating/cooling, as long as the temperature of the fluid considered is non-uniform. As is well-known, molecular and turbulent diffusion tends to relax the system toward thermodynamic equilibrium, i.e., toward an isothermal state, which for a statically stable fluid, will warm up the fluid at high pressure, and cool it down at low pressure. Therefore, because of internal diabatic heating/cooling by molecular/turbulent diffusion, the overall heating experienced by a stratified fluid always occurs at greater pressure than the total cooling, even if the external cooling/heating occur at the same pressure. As a result, internal diabatic heating/cooling due to molecular diffusion explains why laboratory experiments show evidence of circulations developing as the result of surface heating/cooling (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.
In 1925, Sandström was elected a member of the Royal Swedish Academy of Sciences
.
Västerbotten County
Västerbotten County is a county or län in the north of Sweden. It borders the counties of Västernorrland, Jämtland, and Norrbotten, as well as the Norwegian county of Nordland and the Gulf of Bothnia.- Provinces :...
, died 1947, was a Swedish
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
oceanographer.
He is most famously known for conducting a series of classical experiments at Bornö
Borno
-Places:Italy* Borno, Lombardy, a comune in the Province of BresciaNigeria* Borno State* Kanem-Bornu Empire Other:Borno may also refer to a commonly used spam on Xbox live deriving from a game of scrabble...
oceanographic station in Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
that were reported in Sandstrom (1908). 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 ocean 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. Sandstrom's theorem represents an attempt at extending the well known result of classical thermodynamic theory that in order for a heat engine to perform positive work over a cycle, the work of expansion needs to occur at greater pressure than the work of contraction. Sandstrom's theorem is therefore technically true, as long as expansion in the fluid is caused by heating and contraction by cooling, and that greater depths occur at greater pressures. There is an ambiguity, however, as to the meaning of the terms 'heating' and 'cooling' in Sandstrom's theorem. So far, heating and cooling has always been interpreted in the literature as being associated with 'surface heating' and 'surface cooling' respectively. In real fluids, however, molecular and turbulent diffusion always cause internal heating/cooling even in absence of external heating/cooling, as long as the temperature of the fluid considered is non-uniform. As is well-known, molecular and turbulent diffusion tends to relax the system toward thermodynamic equilibrium, i.e., toward an isothermal state, which for a statically stable fluid, will warm up the fluid at high pressure, and cool it down at low pressure. Therefore, because of internal diabatic heating/cooling by molecular/turbulent diffusion, the overall heating experienced by a stratified fluid always occurs at greater pressure than the total cooling, even if the external cooling/heating occur at the same pressure. As a result, internal diabatic heating/cooling due to molecular diffusion explains why laboratory experiments show evidence of circulations developing as the result of surface heating/cooling (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.
In 1925, Sandström was elected a member of the Royal Swedish Academy of Sciences
Royal Swedish Academy of Sciences
The Royal Swedish Academy of Sciences or Kungliga Vetenskapsakademien is one of the Royal Academies of Sweden. The Academy is an independent, non-governmental scientific organization which acts to promote the sciences, primarily the natural sciences and mathematics.The Academy was founded on 2...
.