GEWEX meeting GASS
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GEWEX meeting
GASS
A new case proposed to GASS :Four contrasted regimes in the
Tropics over land
F. Couvreux, F Guichard
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 setup than 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 regimes
Before monsoon In the monsoon
An example of data for the semi-arid regime
Agadez SOP-2Parakou SOP-1Cotonou SOP-1
Fig F. Guichard
The four contrasted regimes
cloudy regimeweak diurnal cycle (3K/ 0.5g/kg)stratocumulus with little rain
Convective wet regimesignificant diurnal cycle (4K, 1g/kg)Very large precipitation
Convective regimelarge diurnal cycle (6K/ 1.5g/kg)Convective systems
Semi-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 mesoscale
Avoir en tête des chiffres pour les précip des 4 régimes, en particulier Parakou SOP-2 et Niamey SOP-2, voire mettre les valeurs moyennes (mm / jour)
1D setup:
1) Initialization & large-scale advection: from ECMWF
AMMA special re-analysis (Agusti-Panareda et al, 2010)
rv q
Surface scheme
Initial profiles
Large-scale advections
__ ECMWF ana- - RS
From stable to less & less stable from cloudy to semi-arid regimes, same content of moisture except the semi-arid regime
Initial conditions from ECMWF analyses
(Couvreux et al., BLM, 2013)
1D setup:
1) Initialization & large-scale advection: from ECMWF
AMMA special re-analysis (Agusti-Panareda et al, 2010)
rv q
Surface scheme
Initial profiles
Large-scale advections
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:
1) Initialization & large-scale advection: from ECMWF
AMMA 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)
rv q
Surface scheme
Initial profiles
Large-scale advections
1D setup:
1) Initialization & large-scale advection: from ECMWF
AMMA 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 convection
scheme, deep convection scheme
rv q
Surface scheme
Initial profiles
Large-scale advections
1D setup:
1) Initialization & large-scale advection: from ECMWF
AMMA 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 convection
scheme, deep convection scheme
4) Simulation length: 10 day-simulation reinitialized every day or not
rv q
Surface scheme
Initial profiles
Large-scale advections
1D-simulations (Meso-NH) over the four regimes
semi-arid: too large diurnal cycle & too high boundary layer
Convective: too correlated rv/ diurnal cycle and too high boundary layer
Convective wet: too moist, too large diurnal cycle and too high boundary layer
Cloudy: too little rv fluctuations & too large fluctuations; closer to saturation
- - - radiosoundings
____ simulation
Different 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)
observations
simulations
Time evolution of cloud cover profiles
regimes
- mean daily value
synoptic variability of daily value
Diurnal cycle of radiative & turbulent fluxes
1D-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* * * radiosoundings
Selected set-up : 10 day runs with composite, diurnally-varying only, large-scale forcings
Conclusion
Set-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 cycles
A land-oriented simple but rich set-up to evaluate the coupling among parameterizations (surface, boundary layer, cloud, convection and radiation)
At least, for Méso-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
'Itemisé' pour insister
References
Gounou 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 144:329–357
Couvreux F, F Guichard, A Gounou, D Bouniol, P Peyrillé, 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, 150:185-214
Guichard 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 375:161–17
The convective regime
Satellite data
Semi-arid regime
Convective regime
Convective wet regime
Cloudy regime
little rain & convective clouds
more rain & convective clouds
heavy rain & convective clouds
little precipitation & very few convective clouds
Ceilometer data
Convective wet regime
Semi-arid regime
Convective regime
Low 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