Dr. Sergej Zilitinkevich
Finnish meteorological Institute
University of Helsinki, Finland
Atmosphere convective planetary boundary layers (C-PBLs) are more complicated in nature than neutrally and stably stratified PBLs. Besides mean flow and usual shear-generated turbulence, C-PBLs involve two types of motion disregarded in conventional theory of turbulence:
(i) buoyancy-driven plumes, which merge to form larger plumes instead of breaking down, as it should be in usual Kolmogorov’s turbulence characterised by the forward energy cascade (Zilitinkevich, 1973)
(ii) large-scale organised structures (fed by potential energy of stratification), which perform non-local transports irrespective of mean gradients of transporting properties.
C-PBLs are strongly mixed and remain growing as long as the layer remains unstable. Penetration of the mixed layer upward into weakly turbulent, stably stratified layer causes essential transport through the C-PBL upper boundary. Hence, adequate representation of C-PBLs in atmospheric models requires knowledge of the C-PBL height and vertical fluxes of energy, matter and momentum at the Earth’s surface, in the C-PBL core, and at the C-PBL upper boundary.
These fluxes are driven mostly by turbulence in the surface layer and entrainment layer, but mostly by organised structures in the C-PBL core (Hellsten and Zilitinkevich (2013). For modelling applications (e.g., transport and dispersion of aerosol; microphysics of clouds) not only the total fluxes, but also the structural and turbulent shares of the fluxes should be determined.
The surface-layer turbulence is, in windy weather, essentially enhanced and, in calm weather, almost completely produced by local shears in horizontal branches of organised structures. This critical nonlocal mechanism was overlooked in conventional local theories, such as the Monin-Obukhov similarity theory, and the convective heat/mass transfer law: , where and are Nusselt and Raleigh numbers.
Revision of the conventional theory is necessary. This paper summarises recent developments along this line including non-local convective heat/mass transfer law (Zilitinkevich et al., 2006), and equations for the C-PBL height and turbulent entrainment (Zilitinkevich 1991, 2012).
June 17, 2014
12:00 pm – 1:00 pm
Location: ST LECTURE HALL
