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SVAT model PLATIN

SVAT model PLATIN

Modelling of biosphere/atmosphere exchange of gases and aerosols depends on the resolution in space and time needed. Whereas local scale Soil-Vegetation-Atmosphere-Transfer (SVAT) models rely on the detailed description of the canopy energy balance of the ecosystem under consideration, regional or national scale models make use of simplifying and integrating assumptions and make use of typical deposition velocities rather than site-specific driving forces (cf. Erisman et al., Environmental Pollution 133, 403-413, 2005). At the European scale, flux estimates are based on large-scale modelled meteorology and concentration fields; ecosystem properties are replaced by those of a vegetation type (cf. Grünhage et al., Atmospheric Environment 38, 2433-2437, 2004). Necessarily, the complexity of details and processes considered in flux modelling decreases with increasing scale in space in time. This means that those generalized approaches must be carefully calibrated by well validated local scale models.

SVAT models serve for two purposes: (1) In agricultural and forest meteorology they are used to calculate water dynamics e.g. to predict irrigation; (2) in the context of the ecotoxicology of air constituents they are needed to derive dose-response relationships (cf. Dämmgen and Grünhage, Environmental Pollution 101, 375-380, 1998).

The SVAT models described in the literature can be grouped into the following categories:

  • schemes with one-dimensional parameterization of energy and trace gas exchange
  • schemes with three-dimensional parameterization of energy and trace gas exchange

The class of SVAT schemes with one-dimensional characterization of the canopy comprises schemes with a one-layered resolution of the vegetation (big leaf and dual source approach), a two-layered resolution (e.g. upper-storey and ground vegetation) or a multi-layered resolution (cf. Grünhage et al., Emvironmental Pollution 109, 373-392, 2000).

SVAT model PLATIN-2

water vapour status of the atmosphereOur SVAT model PLATIN (PLant-ATmosphere INteraction) is based on the big leaf concept which assumes that the canopy be horizontally homogeneous and that the vertical distribution of sources and/or sinks of a scalar (sensible heat, latent heat, ozone or another trace gas) can be represented by a single source and/or sink at the big leaf surface located at the conceptual height z = d + z0,scalar. The model has three major resistance components:

  • a turbulent atmospheric resistance
  • a quasi-laminar layer resistance
  • a bulk canopy or surface resistance

The atmospheric resistance Ratmosphere(d+z0mzref) represents the atmospheric transport properties between the conceptual height of the momentum sink near the big-leaf surface z = d + z0m and a reference height zref above the canopy,where d is the displacement height and z0m is the roughness length for momentum.
     Atmospheric turbulence is driven both by mechanical and thermal forces.
     The latter intensifies the mechanically induced turbulence within periods of
     atmospheric heating during daylight hours (unstable atmospheric stratifi-
     cation), whereas it weakens mechanically induced turbulence during cooling
     periods especially in the night (stable atmospheric stratification). Atmo-
     spheric transport by molecular diffusion can be neglected under turbulent
     conditions.

The quasi-laminar layer resistance Rquasi-laminar layer between momentum sink height z = d + z0m and the conceptual sink/source height for sensible heat and trace gases (including H2O) at z = d + z0h quantifies the way in which the transfer of heat and trace gases (including H2O) differs from momentum transfer.

The bulk canopy or surface resistance Rcanopy describes the influence of the plant/soil system on the vertical exchange of trace gases (including H2O).