Turbulence, horizontal convection, and the ocean’s meridional overturning circulation

Kolmogorov’s 1941 theory describes a turbulent flow as one featuring a cascade of characteristic scales and obeying the law of finite dissipation. Most flows having the first property also have the second. But this is by no means a necessary implication. Horizontal convection is a type of buoyancy driven flow that does not obey to the law of finite dissipation (thus is not turbulent in the sense of Kolmogorov) but appears to have most other properties of a turbulent flow. This, and a number of other connected results, have profound implications on the viability of horizontal convection as a convincing metaphor for the ocean’s meridional overturning circulation: thermal (or thermohaline) forcing alone cannot reproduce most of the essential features of the observed ocean circulation. Recent research shows that only by taking into account the buoyancy forcing and several sources of mechanical mixing in a rotating reference frame a satisfactory depiction of the ocean circulation arises.