Final Report Summary - PBL-PMES (Atmospheric planetary boundary layers: physics, modelling and role in Earth system)
New Energy- and Flux-Budget” (EFB) turbulence-closure theory is developed; and its optimal version is being prepared for implementation into weather-prediction, climate and air-quality models. The theory resolves the problem of the “energetics critical Richardson number” and demonstrates that geophysical turbulence does not degenerate even in supercritically stable stratifications (when smaller-scale flows become laminar) due to the two mechanisms: self-regulation of the buoyancy flux by the counter-gradient heat transfer driven by turbulent potential energy, and efficient exchange between kinetic and potential turbulent energies.
Advanced concept of convective PBL based on the 3-fold decomposition “regular mean flow + chaotic turbulence + self-organised structures” is developed and verified against available data and topical large-eddy simulations. The concept includes (i) non-local heat/mass transfer laws accounting for the enhancing effect of the near-surface structural motions; (ii) advanced PBL-height and turbulent entrainment equations; and (ii) analytical treatment of organised structures. This high-risk/high-gain research effort provides advanced framework for modelling geophysical convection.
Advanced models of stably and neutrally stratified PBLs, including recently recognised conventionally-neutral PBL (archetypal over the ocean) and long-lived stable PBL (archetypal over continents at high latitudes), are derived and employed to develop new surface-flux algorithms accounting for interactions between the surface layer and PBL core. This analysis reveals limits of applicability of the familiar Monin-Obukhov similarity theory. Essential stability dependences of the aerodynamic roughness length and displacement height are established and verified against data from observations over forest- and urban-canopies. A number of real-time LES studies parallel to field measurement are performed and used to enrich outputs from observations, e.g. for turbulent fluxes over sea ice in the Arctic, and for urban air-quality hazards under very stable PBL. Advanced methods of retrieving the PBL height from the ceilometer and sodar observations are developed and employed in the FMI air-quality models CAR-FMI and SILAM. New “Helsinki Urban Boundary Layer Network” has been set up. A new concept of the PBL-climate feedback accounting for strong the PBL thermal sensitivity is developed and employed to explain up to 70% of the observed temperature trends and variability of climate change at high latitudes. The EFB closure and PBL parameterizations are being prepared for implementation into weather, air-quality and climate models in the EU: HARMONIE and AROME (>10 EU countries), Enviro-HIRLAM (Denmark), and prospectively in USA: WRF.