Dynamical downscaling of wind fields in stratified flow: a high resolution mesoscale approach Pedro Miranda, R Tomé, A Rodrigues, J Palma, F Castro, J Pinto, E Dutra University of Lisbon, CGUL, IDL, Portugal University of Porto, CEsA, Portugal

Issues Merging meteorology and mechanical engineering approaches to wind simulation What resolution is needed/possible to get the most from mesoscale meteorological models? Is it worth using even higher resolution nested CFD codes? Forecast and mapping: how different are they?

What is in a weather prediction model? Resolved scales: full dynamic equations (hydrostatic or non-hydrostatic ) Problems initial state, boundary conditions interaction with unresolved scales (higher-resolution?) misrepresentation of non-dynamical processes Unresolved scales and processes Orography (small and some mesoscale)> local wind Clouds Turbulence... ECMWF (T511L60~40km) 3km

Models Meteorological Boundary conditions from ECMWF analysis MM5 (nested, down to 3  3, 2  2 or 1  1 km), full physics, 5 years 54x54km  18x18  6x6  (3x3 or 2x2 or 1x1) WRF (nested domains, down to 2  2 km), full physics, 1 month MesoNH (nested domains, down to 2  2 km), full physics, 1 month NH3D (single domain, 1.5  1.5km), simple physics CFD code Boundary Conditions from NH3D VENTOS, dry, unrotating, adiabatic, ~300  300 m, 1 week

“Real” 100x100m Model 2x2km

Dec 2002

Linear model OBS Linear NH3D

Resolution 3km 1.5km

u v

December 2002

Resolution (MM5) Best mast (Nov 2005) Nov 2005 Models (MM5, WRF,

Coupling NH3D (1.5km) with VENTOS (300m)

Nov 2005 Mean wind 2x2km

Final thoughts Results are model dependent and resolution dependent (same analysed boundary conditions) “High” mesoscale resolution is needed (e.g. 2km) There may be gains in higher resolution (100m) if the microscale model is good There is a clear need for improvement! Remember: this is a very rough case in terms of topography. Results in mainland Portugal are often better