Cellular convection embedded in the convective planetary boundary layer surface layer

摘要

Cellular convection was first studied in the laboratory by Benard [Ann. Chim. Phys. 23 (1901) 62–144] and Rayleigh [Phil. Mag. Ser. 6 (1916) 529–546] investigated these motions from a theoretical perspective. He defined a dimensionless number, now called the Rayleigh number, which is the ratio of convective transport to molecular transport, and found that if a certain critical value is exceeded, cellular convection occurs. Mesoscale cellular convection (MCC) is a common occurrence in the planetary boundary layer. Agee [Dyn. Atmos. Oceans 10 (1987) 317–341] discussed the similarities and differences of MCC and classical Rayleigh-Benard convection. A similar cellular pattern can be seen in the convective boundary layer (CBL) surface layer. It is known that in the CBL, air near the surface converges into thermals producing updrafts. This produces a ‘spoke’ type pattern similar to the mesoscale cellular or Rayleigh-Benard convection. This paper will focus on applying Rayleigh-Benard convection criteria, using a linearized perturbation method, to the CBL surface layer produced by Large Eddy Simulation (LES). We will investigate the length scales of turbulence in the CBL surface layer and compare them to those predicted from linear theory. Similarities and differences will be discussed between the LES produced surface layer and classical Rayleigh-Benard convection theory.