On the role of the planetary boundary layer depth in the climate system

摘要

The planetary boundary layer (PBL) is a part of theEarth's atmosphere where turbulent fluxes dominate vertical mixing andconstitute an important part of the energy balance. The PBL depth, h, isrecognized as an important parameter, which controls some features of theEarth's climate and the atmospheric chemical composition. It is also knownthat h varies by two orders of magnitude on diurnal and seasonal timescales. This brief note highlights effects of this variability on theatmospheric near-surface climate and chemical composition. We interpret heatcapacity parameter of a Budyko-type energy balance model in terms ofquasi-equilibrium h. The analysis shows that it is the shallowest,stably-stratified PBL with the smallest h that should be of particularconcern for climate modelling. The reciprocal dependence between the PBLdepth and temperature (concentrations) is discussed. In particular, theanalysis suggests that the climate characteristics during stably stratifiedPBL episodes should be significantly more sensitive to perturbations of theEarth's energy balance as well as emission rates. On this platform, h fromERA-40 reanalysis data, the CHAMP satellite product and the DATABASE64 datawere compared. DATABASE64 was used to assess the Troen-Mahrt method todetermine h through available meteorological profile observations. As ithas been found before, the shallow PBL requires better parameterization andbetter retrieval algorithms. The study demonstrated that ERA-40 and CHAMPdata are biased toward deeper h in the shallow polar PBL. This, coupledwith the scarcity of in-situ observations might mislead the attribution ofthe origins of the Arctic climate change mechanisms.