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Turbulent exchange of energy, momentum, and reactive gases between high vegetation and the atmospheric boundary layer

  • Shapkalijevski, M.M.
Publication Date
Jan 01, 2017
Wageningen University and Researchcenter Publications
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This thesis deals with the representation of the exchange of energy, momentum and chemically reactive compounds between the land, covered by high vegetation, and the lowest part of the atmosphere, named as atmospheric boundary layer (ABL). The study presented in this thesis introduces the roughness sublayer (RSL), the layer just above the tall vegetation canopy in which the atmospheric flow is directly affected by the presence of roughness elements, as an important part of the ABL system. Our focus is on the exchange of the thermodynamic, as well as the chemical properties of the boundary layer. Our methodology combines observational analysis using high resolution meteorological and chemistry measurements from the Canopy Horizontal Array Turbulence Study (CHATS) and modelling framework of the soil-vegetation-atmospheric boundary layer system. The systematic investigation in this thesis showed the relevance of the RSL for the turbulent exchange processes between the atmosphere and the land surface characterized by high vegetation. More specifically, we explained and discussed how the turbulence parameterization within the roughness sublayer is strongly dependent on canopy-phenology (canopy leaf state) and atmospheric-stability changes, and provided parameterization formulations for . Our modelling analysis further showed that the CHATS boundary-layer dynamics are mainly affected and controlled by the large-scale processes (advection and subsidence), while the effect of the canopy and the roughness sublayer were relatively small. Near the canopy top however, the the canopy had a significant impact on the modelled boundary layer state variables (wind speed, potential temperature and specific humidity) and the corresponding turbulent transfer coefficients (drag coefficients for momentum and scalars), as supported by the observations. With respect to the exchange of reactive compounds, we diagnosed twice-larger magnitude of the ozone deposition fluxes when the roughness sublayer effects are taken into account in the flux-gradient relationship, compared to the method which neglects these effects. Thus, neglecting the roughness sublayer effects in the surface flux parameterization schemes of ozone in atmosphere-chemistry models can lead to significant overestimation of the ozone diurnal mixing ratio in the boundary layer. By studying the high vegetation-atmosphere exchange processes, their quantification, and testing methods for their parameterization, we contribute to improve our understanding and representation of the roughness sublayer-atmospheric boundary-layer system.

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