Tentative Title: "Convection Cells in the Planetary Boundary Layer: Origin and Reduced Modelling".

Turbulent convection self-organises on large scales into circulation cells; an example of coherent structures in turbulent fluid flow. In the convective bounary layer (CBL), properties inside the surface layer and entrainment zone are modified by the interaction between these large-scale circulations (LSCs) and small-scale turbulence. The representation of this interaction remains a challenge for the modelling community due to past inability to capture the smallest scales of motion in the fully turbulent regime. With current computational capacity, direct numerical simulation (DNS) provides the opportunity to make headway in our understanding of the effects of scale interactions.

 

In addition, the large-scale cellular structures observed in the CBL bear a striking resemblance to those observed in other free convective regimes such as Rayleigh-Bénard convection. Motivated by this apparent similarity, we investigate the following questions:

 

  1. What are the length and time scales that characterise LSCs and allow us to extract them from the flow field? 
  2. What are the effects of scale interactions, especially inside the surface layer and entrainment zone? How do the large-scales affect small-scale properties and is that altered by changes in the large-scales in different free convective regimes?
  3. How do our results depend on the Rayleigh number? Do we observe some degree of statistical similarity beyond a certain order of magnitude? Are we then able to extrapolate our results to the real atmosphere, despite the comparatively small Rayleigh numbers we are able to achieve in our numerical simulations?