Intermittent Turbulence in a Global Ocean Model

O ne of the hallmarks of turbulence is intermittent behavior, such as the sudden and unpredictable gusts of wind in the north of Scotland. Intermittency is related to the existence of intense and sparse coherent structures, as in atmospheric fronts, hurricanes, and tornadoes, and to small-scale vortex filaments in fully turbulent flows. Intermittent behavior has been observed in the ocean, but its implications are not fully understood. This is because computer models are unable to incorporate the full range of scales involved: from the planetary scale ( ∼ 104 km) down to the scale at which energy is dissipated ( ∼ 1 mm). A new numerical study of the global ocean breaks the problem into two parts by simulating the dynamics at large scales (greater than roughly 1 km) and then approximating how energy cascades to smaller scales [1]. The researchers—Brodie Pearson and Baylor Fox-Kemper from Brown University in Rhode Island—find spatial intermittency in the dissipation of kinetic energy at large scales where one would expect waves to smooth out fluctuations in the flow. The results imply that some regions in the ocean may dissipate much more energy than other regions, which could affect how oceanographers estimate the energy budget of the ocean from localized observations.