The Role of Roughness Sublayer Dynamics Within Surface Exchange Schemes
- 340 Downloads
Turbulence above and within canopies has characteristics distinct from that over rough surfaces. The vertical transport of momentum and scalars is dominated by coherent structures whose origin is now thought to be the result of the unstable inflexion in the profile of the mean wind speed established by the application of canopy drag. This distinctive property leads to the failure of the standard Monin–Obukhov flux–profile relationships over homogeneous canopies, relationships that are assumed in many surface exchange schemes within numerical weather prediction and general circulation models. A modification of the flux–profile relationships is presented that incorporates the effects of the canopy turbulence. The subsequent impacts on the evolution of the surface energy balance and boundary-layer state are investigated within a simple numerical model for the evolution of the boundary layer and canopy state. By comparing cases with and without the modification it is shown that canopy-generated turbulence can lead, not only to the alteration of the flux–profile relationships above the canopy, but also to a different evolution of the surface energy balance and differences in near-surface conditions that would be significant in numerical weather prediction. More fundamentally, the modifications to the flux–profile relationships imply that parameters such as the roughness length and displacement height for canopies should not be considered as invariant properties, but rather as properties that depend on the flow and hence vary systematically with the diabatic stability of the boundary layer.
KeywordsBoundary layer Canopy Energy balance Numerical weather prediction Roughness sublayer
Unable to display preview. Download preview PDF.
- Chen F, Schwerdtfeger P (1989) Flux-gradient relationships over tall plant canopies. Q J Roy Meteorol Soc 58: 93–117Google Scholar
- Essery R, Best M, Cox P (2001) MOSES 2.2 technical documentation. Hadley centre technical, note 30. Hadley Centre, UK Met Office, UK, 30 ppGoogle Scholar
- Finnigan J (2004) Advection and modeling. In: Lee X, Massman W, Law B (eds) The handbook of micrometeorology: a guide for surface flux measurements and analysis. Atmospheric and oceanographic sciences library, vol 29. Kluwer Academic Publisher, Dordrecht, pp 209–244Google Scholar
- Garratt JR (1980) Surface influence on vertical profiles in the atmospheric near-surface layer. Q J Roy Meteorol Soc 96: 211–255Google Scholar
- Garratt JR (1992) The atmospheric boundary layer. Cambridge University Press, U.K., 316 ppGoogle Scholar
- Kowalczyk EA, Wang YP, Law RM, Davies HL, McGregor JL, Abramovitch G (2006) The CSIRO Atmosphere Biosphere Land Exchange (CABLE) model for use in climate models and as an offline model. CSIRO Marine and Atmospheric Research Paper 013, CSIRO Marine and Atmospheric Research, AustraliaGoogle Scholar
- Monteith JL, Unsworth MH (2008) Principles of environmental physics. Elsevier, New York, 418 ppGoogle Scholar
- Mynemi RB, Hoffman S, Knyazikhin Y, Privette JL, Glassy J, Tian Y, Wang Y, Song X, Zhang Y, Smith GR, Lotsch A, Friedl M, Morisette JT, Votava P, Nemani RR, Running SW (2002) Global products of vegetation leaf area and fraction absorbed PAR from year one of MODIS data. Remote Sens Environ 83: 214–231CrossRefGoogle Scholar