Air-Water Interface

The fluid motion at the interface between the oceans and the atmosphere is crucial for their interchange of mass (constituents), momentum and energy. This image shows the temperature field at the water-air interface, looking from above. The turbulent motion inside the water is caused by surface cooling. The center of the cells, in dark, corresponds to relatively warm regions ascending towards the surface (moving out of the screen). The brighter contours of the cells, only millimeters wide, indicate water a few degrees colder, plummeting as thermal sheets. The observed cellular pattern is typical in buoyancy-driven flows -- it is the signature of ordered motions amid random fluctuations.

Cloud-Top Boundary

Mixing at the cloud boundaries play a fundamental role in the evolution of clouds, and clouds can have in turn a profound impact on planetary scale circulations. This image depicts the turbulent structure of the stratocumulus cloud-top inside a vertical plane in terms of the magnitude of the temperature gradient,  resolving scales from 4 meters down to  about 4 milimeters. The upper horizontal stripe corresponds to the inversion that separates the turbulent cloud below from the warm clear sky above. The turbulent motion is created by the evaporation of the droplets in a thin region next to that inversion, which cools locally the fluid mixture and leads to finger structures plummeting into the cloud. 

Turbulence Intermittency

Measurements in external turbulent flows are characterized by an alternation between intervals with a rapidly varying signal and intervals with a slowly varying signal, or even complete calm, depending on the property being measured. This feature is referred to as (outer or external) intermittency and it reflects the coexistence of turbulent and non-turbulent regions. This figure illustrates this property in terms of the scalar gradient inside a horizontal plane in the upper part of the mixing layer that develops as a consequence of the relative motion of two superimposed regions (fluid flows from right to left). We can see very clearly the strong and sharp boundaries that separates the turbulent patches from the black, non-turbulent region.