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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