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IOMASA Report Summary

Project ID: EVK3-CT-2002-00067
Funded under: FP5-EESD
Country: Sweden

Improved turbulence scheme and flux parameterisation

Practically oriented flux-calculation techniques based on correction functions to the neutral drag and heat/mass transfer coefficients have been further developed. In the traditional formulation, the correction functions depend only on the bulk Richardson number. However, data from measurements of turbulent fluxes and mean profiles in stable stratification over different sites exhibit too strong variability in this type of dependencies. Indirect evidence from climate and weather prediction modelling also suggests that the traditional flux calculation technique is not sufficiently advanced. It is conceivable that other mechanisms besides the surface-layer stratification and, therefore, other arguments besides the bulk Richardson number must be considered.

The proposed technique accounts for a generally essential difference between the roughness lengths for momentum and scalars and includes a new effect of the static stability in the free atmosphere on the surface layer scaling. Recommended correction functions depend, besides bulk Richardson number, on one more stability parameter, involving the Brunt-Väisälä frequency in the free atmosphere, and on the roughness lengths.

The project has resulted in an improved surface flux treatment and a new surface scheme using OSI-SAF ice concentrations implemented in HIRLAM. However, the flux treatment is not yet implemented over sea ice and it also need to be adapted to the new snow and ice parameterisation in HIRLAM.

Related information

Reported by

Research Dept., SMHI
SE-60176 Norrkjöping
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