Statistics – Applications
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996esasp.392..321f&link_type=abstract
Environment Modelling for Space-based Applications, Symposium Proceedings (ESA SP-392). ESTEC Noordwijk, 18-20 September 1996. E
Statistics
Applications
Scientific paper
The representation of the Planetary Boundary-Layer (PBL) is essential for use of General Circulation Models (GCM) results for planetary exploration missions design (prediction of near surface profiles of wind and temperature means, as well as turbulent fluctuations). However, the representation of the PBL was considered of secondary importances in early developments of General Circulation Models (GCM). Now, long duration simulations for climate modeling demand higher accuracies and efforts are required for the design of precise PBL models compatible with GCM computational constraints. A PBL parametrisation has been designed at the Laboratoire de Meteorologie Dynamique, CNRS, that allows an accurate description of Martian low atmosphere at numerical costs fully compatible with GCM implementations. The starting point is a level 2.5 second-order closure model of the Turbulent Kinetic Energy (TKE) evolution. This model is widely used for detailed PBL analysis but is incompatible (as such) with typical temporal and vertical GCM discretizations: time steps of the order of 30 minutes and 20 to 30 levels for total atmosphere vertical extension. For such discretizations, numerical oscillations are encountered between TKE production and wind shear evolution. This problem is particularly severe for Mars where diurnal fluctuations are very large. At nightfall, the PBL shrinks violently with a strong TKE decrease that allows the creation of an intense low level jet. This jet creates wind shears that are, in turn, the origin of TKE production: this compensation effect is essential and cannot be modeled simply with time steps of the order of half an hour. The proposed solution makes use of a simplified TKE model coupled with a local wind shear model: (i) the vertical diffusion of TKE is neglected; (ii) local wind shear temporal evolution assumes constant conditions at non adjacent levels. The corresponding numerical scheme is very simple and robust and allows a precise representation of near surface conditions in particular of wind standard deviations due to turbulent fluctuations. Validation procedures are detailed and GCM simulation results are compared with Viking landers measurement data.
Deleersnijder Eric
Forget Francois
Fournier Richard
Hourdin Fréderic
Lahellec A.
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