Momentum and heat flux parametrisation at Dome C, Antarctica: a sensitivity study

The rich meteorological dataset of Concordia station at Dome C, East Antarctic Plateau, has enabled to assess the sensitivity of the momentum and heat fluxes estimation to surface roughness and atmospheric stability in this region. Our study reveals that: i) Because of the preferential orientation of snow micro-reliefs (sastrugi), the roughness length for momentum z0 has been shown to vary by more than two order of magnitude depending on the wind direction. Consequently, estimating the turbulent fluxes with a realistic but constant z0 of 1mm leads to a mean friction velocity bias of 24% in near-neutral conditions. ii) The flow regime dependency of the ratio between the roughness length for heat z0t and z0 has been shown to be reasonably in agreement with previous theoretical models. Correct estimations of the heat flux are obtained with z0t lower by one order of magnitude than z0. iii) The wide range of atmospheric stability at Dome C make the flux very sensitive to the choice of the stability functions. A priori adapted stability function models have been evaluated and they generally underestimate the dimensionless temperature gradient. As these models differ as the stability parameter z/L increases, heat flux and friction velocity relative differences reaching 100% are observed as z/L becomes greater than 1. iv) The shallowness of the stable boundary layer is responsible for a significant sensitivity to the height of the temperature and wind data used to estimate the fluxes. Consistent flux results are obtained for atmospheric measurement heights up to 2m. For climate model simulations, we thus recommend a first model level below 2m. The results of this sensitivity study constitute a new step to improve and develop atmospheric boundary layer parametrisations over Antarctica in climate models. Antarcticclimate·stableboundarylayers·roughnesslengths·modelsparametrisations