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Sixième réunion des utilisateurs de Méso-NH, Toulouse, 13-14 octobre 2011

l'impact de la représentation des lacs dans des simulations Meso-NH Rui Salgado Centro de Geofísica de Évora Universidade de Évora. Sixième réunion des utilisateurs de Méso-NH, Toulouse, 13-14 octobre 2011. Summary. How important are the representation of lakes (NWP)

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Sixième réunion des utilisateurs de Méso-NH, Toulouse, 13-14 octobre 2011

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  1. l'impact de la représentation des lacs dans des simulations Meso-NH Rui Salgado Centro de Geofísica de Évora Universidade de Évora Sixième réunion des utilisateurs de Méso-NH, Toulouse, 13-14 octobre 2011

  2. Summary • How important are the representation of lakes (NWP) • Flake: initial conditions and parameters • 3D simulation Meso-NH – Surfex – FLake • Impact of the FLake on the flow over a lake (Alqueva) • THUMEX (Radiation measures)

  3. How important is the lake representation in NWP (example) SON JJA Sensitivity of 48-hour near surface temperature forecast (LAKE – NOLAKE) - Sets of 10-day forecasts covering one full year (1988) at 50 km resolution with the operational IFS. Two experiments were performed with (LAKE) and without (NOLAKE) FLake activated. Balsamo, G., R. Salgado, E. Dutra, S. Boussetta, T. Stockdale, M. Potes, (2011). ECMWF Tech. memo 648.

  4. Impact of FLake on NWP (IFS) • Impact of 48-hour T2m forecasts (valid at 00 UTC) for LAKE compared to NOLAKE, • verified against the ECMWF T2m analysis: Mean Absolute Error difference for JJA 2008. • Negative values indicate an improvement (MAE reduction) • A positive impact in spring and summer particularly over the North American lakes region and the European large lakes areas. • In Winter, deteriorates T2m over central Canada while it improves in the eastern North America • In Autumn the impact is milder, with improvement over Scandinavia • Overall the impact is positive

  5. FLake in NWP models Surfex • Flake is implemented: • Regional weather forecast of the German weather service (operational after 2010) • UK-MetOffice • (Rooney et al 2010) • Swedish Meteorological and Hydrological Institute • (Samuelson, 2010) • ECMWF (IFS) • SURFEX • The performance of FLake was evaluated during the Lake Model Intercomparison Project (Lake-MIP, Stepanenko et al. 2010) FLake • FLake: Fresh-water Lake model FLake (Mironov et al. 2010) • Two-layer parametric representation of the evolving temperature profile • integral budgets of heat and kinetic energy. • The thermocline is described using the concept of self-similarity (assumed shape) of the temperature profile.

  6. Flake: Initialization • The use of the FLake lake model inside an weather forecast system requires the knowledge of some parameters and the initial conditions of its variables. • Parameters: • Depth • Extinction coefficient of solar radiation in water • Water surface radiative proprieties (albedos, emissivity) • Lake variables are currently not treated by the data assimilation systems. • One possible solution is to create a climate of FLake variables from off-line long periods simulations

  7. Global lake depth data base Lake depth is a crucial field controlling the water body thermal capacity, as demonstrated by many authors lake depth data provided by Kourzeneva et al. (2010) 30sec arc resolution

  8. Climatologies for cold start simulations • Example • Climatological lake mixed-layer temperature • (a) winter (DJF) • (b) spring (MAM) • (c) summer (JJA) • (d) autumn (SON) • generated by the • Lake-planet experience: • Off-line simulation with HTESSEL+FLake • Lakes overall (lake fraction = 1 over all grid points) • Forcing: ERA-Interim reanalysis 1989 – 2009 • N128 resolution (~80km)‏

  9. 3D simulation Configuration Avec grid-nesting (Two way) South-East of Portugal Alqueva artificial lake

  10. 3D simulation Configuration

  11. 3D Simulation Initial Conditions and parameters Alqueva field campaign Summer 2007 15/07/2007 18:00 TMNW T_BOT T_B1 H_ml H_b1 TS 289.27 285.42 282.25 4.36 0.78 298.04 Lake depth: 40m Extinction coefficient: 3.5m

  12. improve T2m Mean values over lake

  13. improve surface fluxes

  14. Effect on T2m Hu2m and wind near surface horizontal fields

  15. Boundary layer

  16. The use of the FLake lake model inside an weather forecast system requires the knowledge of some parameters and the initial conditions of its variables. • Parameters: • Depth • Extinction coefficient of solar radiation in water • Water surface radiative proprieties (albedos, emissivity) • Lake variables are currently not treated by the data assimilation systems. • One possible solution is to create a climate of FLake variables from off-line long periods simulations

  17. THAUMEX field campaign POI 24 August measurement of spectral radiative flux at several levels estimation of the Extinction coefficient (spectral)

  18. THAUMEX field campaign POI 24 August Reflectance spectral

  19. Conclusions • The effects of the implementation of FLake are visible on mesoscale short-range simulations: • in the case studied, the impact of T2m > 2ºC • it improves the representation of surface fluxes of sensible heat, latent heat and momentum • the effects are manly concentrated over the lake • The effect on the circulation is weak, but still visible • ongoing work • explore THAUMEX data – obtain extinction coefficient

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