A Review of Modeling Ocean Circulation From Science 26, 5229

Lucas Rockwell


Although systematic measurements of the ocean have been taken since the 1880s, the ocean is relatively undersampled; especially when compared to the atmosphere. This lack of data led to the thought that the oceans were relatively stable over time, and hence trivialized attention given to the important topic of ocean circulation (Semtner 1995: 1379). However, scientists have come to realize that not only is ocean circulation dynamic, but it also plays a crucial role in global weather phenomena such as El Nino (Cubasch 1991: 76; Semtner 1995: 1379).

To counter this problem of a lack of data for a system which plays such a key role in the global climate system, scientists have employed the use of computers, and more recently, the use of supercomputers.

Ocean modeling has evolved extensively since the first decade of modeling at the Geophysical Fluid Dynamic Laboratory back in the 1960s. Today, a decades worth of simulation, a feat which used to take years, can be completed in a month. This is accomplished by using computers which are capable of performing about 10 billion operations per second; scientists hope a computer capable of performing a trillion operations per second will be produced by the turn of the next century (Semtner 1995: 1382).

As the calculation power of computers increases, scientists are able to not only put more complicated data into the machines such as surface height, heat, and salt content but also get more sophisticated data out like long time-span consequences of biology or geochemistry.

One particularly important contribution faster computers has made to ocean modeling has been the ability to decrease distances between grid points. Early computers used grids some 20 degrees apart, while present day computers can use grids which are only 1/6 of a degree apart (Semtner 1995: 1380-1381). This increase in precision has enabled scientists to simulate real-world ocean circulation with more accuracy. As accuracy of real-world simulations has increased tested by comparing models to historic data predictions of current and future ocean effects on climate have been, and will continue to be, stated with more authority (Semtner 1995: 1380, 1382).

Another very important aspect of faster computers is the ability to link ocean and atmospheric models. In the past, time scale differences ranging from one day for the atmosphere to 1000 years for the deep ocean have prohibited equilibrium from being reached between the two (Cubasch 1991: 87).

Time scale differences are very important considerations as Albert Semtner points out by noting that more powerful computers are necessary due to the fact that the fundamental scale of motion, the internal radius of deformation, is ten times smaller in the ocean than in the atmosphere (1995: 1381). This difference therefore allows disturbances to have the same impact on the ocean as those acting on the atmosphere with 10 times the magnitude, and hence 10 times more computing power is necessary to model them.

Semtner recognizes that both ocean and atmospheric models need to be coupled to determine the effect on global climate more accurately. Semtner, like Cubasch, points out that these "...efforts require continued growth in computer power" (1995: 1385). However, Cubasch also notes that not only is increased computing power necessary to link the myriad of models, but so too is interdisciplinary cooperation (1991: 89).

Interdisciplinary cooperation is perhaps the most important aspect, for the free flow of knowledge is essential to not just understanding how oceanic events impact climate, but also how scientists and policy makers, in conjunction with the Earth's people, can begin to deal with this knowledge in meaningful ways.

References Cited