GEWEX meeting GASS

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A new case proposed to GASS : Four contrasted regimes in the Tropics over land F. Couvreux, F Guichard. GEWEX meeting GASS. Motivations for this case of modelling. A new case proposed for an intercomparison exercise Only a few cases over Tropical lands (only 1 for semi-arid conditions) - PowerPoint PPT Presentation

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  • Motivations for this case of modelling A new case proposed for an intercomparison exercise Only a few cases over Tropical lands (only 1 for semi-arid conditions) A variety of conditions: four different cases Observations available to evaluate the cases 1D setup already available A slightly different setupthan usual GCSS intercomparison : 10 day-long simulation: allow for the biases to develop less constrained setup, powerful identification of surface-atmosphere model biases Possible interaction with the ALMIP2 project

  • Scientific objectives To evaluate the performance of the models over four contrasted regimes in Tropical lands (focus on diurnal & synoptic time scales):- low heavily cloudy boundary layer (wet soil)- deep tropical convection (wet soil) with heavy precipitation- deep subtropical convection with less precipitation- semi-arid conditions (with high, less cloudy boundary layers over dry soil) To analyze how the couplings among cloud, convection, boundary-layer and surface processes vary among those different regimes To determine how biases change with in certain regimes

  • Methodology

    1) Use observations to build a set of realistic 10-day cases(incorporating diurnal cycle and synoptic fluctuations...)

    2) Simplify the set up in a way that preserve robust features of the model behaviour(e.g. as shown hereafter removing synoptic fluctuations does not modify the 10-day mean diurnally varying results)

  • Data available: Radiosoundings (8 RS/ per day ) good sampling of the diurnal cycle Surface fluxes measurements (radiative & turbulent) Cloud characteristics: ARM station (vertical profiles of clouds for two regimes), ceilometers, satellite products Precipitation information (rain gauges, satellite products) Aerosol content (AOD from AERONET)(Gounou et al., BLM, 2012)10-day observations over 4 sites at 2 periods of the year: similitudes among the different periods = definition identification of 4 regimesBefore monsoonIn the monsoon

  • An example of data for the semi-arid regime

  • Fig F. GuichardThe four contrasted regimescloudy regimeweak diurnal cycle (3K/ 0.5g/kg)stratocumulus with little rainConvective wet regimesignificant diurnal cycle (4K, 1g/kg)Very large precipitationConvective regimelarge diurnal cycle (6K/ 1.5g/kg)Convective systemsSemi-arid regimeVery large diurnal cycle (9K/ 6 g/kg)Shallow cumulus and aerosols(Gounou et al., BLM, 2012)Diurnal cycle of WHAT? Of BL thermolarge mesoscaleAvoir en tte des chiffres pour les prcip des 4 rgimes, en particulier Parakou SOP-2 et Niamey SOP-2, voire mettre les valeurs moyennes (mm / jour)

  • 1D setup:Initialization & large-scale advection: from ECMWFAMMA special re-analysis (Agusti-Panareda et al, 2010)__ ECMWF ana- - RSFrom stable to less & less stable from cloudy to semi-arid regimes, same content of moisture except the semi-arid regimeInitial conditions from ECMWF analyses(Couvreux et al., BLM, 2013)

  • 1D setup:Initialization & large-scale advection: from ECMWFAMMA special re-analysis (Agusti-Panareda et al, 2010)Large-scale forcings from ECMWF analyses(exemple of potential temperature tendency)Low-level advection for semi-arid regime, vertical advection for convective wet regime

  • 1D setup:Initialization & large-scale advection: from ECMWFAMMA special re-analysis (Agusti-Panareda et al, 2010)2) Surface initialization: soil properties & vegetation from ECOCLIMAP, surface properties (soil moisture & temperature) from AMMA land-surface model intercomparison project (Boone et al, 2009)

  • 1D setup:Initialization & large-scale advection: from ECMWFAMMA special re-analysis (Agusti-Panareda et al, 2010)2) Surface initialization: soil properties & vegetation from ECOCLIMAP, surface properties (soil moisture & temperature) from AMMA land-surface model intercomparison project (Boone et al, 2009)3) Parameterizations activated:Surface scheme, radiation scheme,Turbulence scheme, shallow convectionscheme, deep convection scheme

  • 1D setup:Initialization & large-scale advection: from ECMWFAMMA special re-analysis (Agusti-Panareda et al, 2010)2) Surface initialization: soil properties & vegetation from ECOCLIMAP, surface properties (soil moisture & temperature) from AMMA land-surface model intercomparison project (Boone et al, 2009)3) Parameterizations activated:Surface scheme, radiation scheme,Turbulence scheme, shallow convectionscheme, deep convection scheme4) Simulation length: 10 day-simulation reinitialized every day or not

  • 1D-simulations (Meso-NH) over the four regimessemi-arid: too large diurnal cycle & too high boundary layerConvective: too correlated rv/ diurnal cycle and too high boundary layerConvective wet: too moist, too large diurnal cycle and too high boundary layerCloudy: too little rv fluctuations & too large fluctuations; closer to saturation- - - radiosoundings____ simulationDifferent biases for the different regimes: too moist for the moist regimes, too dry for the dry regimes(Couvreux et al., BLM, 2013)

  • (Couvreux et al., BLM, 2013)observationssimulationsTime evolution of cloud cover profilesregimes- mean daily valuesynoptic variability of daily valueDiurnal cycle of radiative & turbulent fluxes1D-simulations (Meso-NH) over the four regimesEvaluation of surface budget: clear colors = observations; dark colors simulations

  • Summary of the biases of Meso-NH simulation

  • Towards a simplified set-up

  • Toward a simplified set-up 10-day runs -> enlarge the biases already visible in 1-day runs quite informative of model biases same conclusions with composite large-scale forcings / synoptically varying large-scale forcings constant (no diurnally varying) large-scale forcings induce some modifications of the diurnal cycle 10 1-day simulations re-initialised every morning for the 4 regimes- - - 10 1-day run___ 10-day run___ 10-day constant LS advection* * * radiosoundingsSelected set-up : 10 day runs with composite, diurnally-varying only, large-scale forcings

  • ConclusionSet-up available for observationnaly-based 1D-runs (4 different regimes for 10-day simulations with composite large-scale forcings)Observations available for evaluation: composite of the diurnal cyclesA land-oriented simple but rich set-up to evaluate the coupling among parameterizations (surface, boundary layer, cloud, convection and radiation)At least, for Mso-NH, the biases involve 1) the representation of clouds (too many for the cloudy regimes, too little few for the convective and semi-arid regimes) and 2) the coupling with the surface

    Calendar: to propose the case for Jan 2016

    Ici et ailleurs: le mot 'composite', je ne suis pas sure que les gens comprennent, c'est un cycle diurne moyen en fait 'Itemis' pour insister

  • ReferencesGounou A, Guichard F, Couvreux F, 2012: Observations of diurnal cycles over a West-African meridional transect: pre-monsoon and full-monsoon seasons. Boundary-Layer Meteorol 144:329357Couvreux F, F Guichard, A Gounou, D Bouniol, P Peyrill, M Kohler, 2014: Modelling of the thermodynamical diurnal cycle in the lower atmosphere: a joint evaluation of four contrasted regimes in the Tropics. Boun-Lay Meteor, 150:185-214Guichard F, Kergoat L, Mougin E, Timouk F, Baup F, Hiernaux P, Lavenu, 2009: Surface thermodynamics and radiative budget in the Sahelian Gourma: seasonal and diurnal cycles. J Hydrol 375:16117

  • The convective regime

  • Satellite dataSemi-arid regimeConvective regimeConvective wet regimeCloudy regimelittle rain & convective clouds

    more rain & convective clouds

    heavy rain & convective clouds

    little precipitation & very few convective clouds

  • Ceilometer dataConvective wet regimeSemi-arid regimeConvective regimeLow cloud bases very numerous in the convective wet regime____ occurrence from 0-3km------ occurrence from 3-6km

  • Budget of and rv in the simulations

  • Results of simulation for Meso-NH