Pr

1
The 10th of July 2006 over Niamey a Golden Case
of Daytime Moist Convection in a Semi-Arid
Environment
a case-study built by Catherine Rio (1),
Françoise Guichard (1), Fleur Couvreux (1)? from
observations analysed by Marie Lothon (2), Michel
Chong (2), Bernard Campistron (2), Dominique
Bouniol (1)?
system
Meteosat IR-10.8 image at 1800 UTC.

1. Météo-France, CNRM/GAME/GMME/MOANA, CNRS,
   Toulouse, France
2. Laboratoire dAérologie, CNRS, Toulouse/Lannemezan
   , France

GCSS/CFMIP Meeting 12th of June 2009, Vancouver,
Canada
2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
Case set-up
Initial profiles

• Warm and moist low levels at 6am

• The low level jet brings cold and moist air
• in the low levels in the morning

• Radiative tendencies prescribed

• An ascendance of 1.5 cm/s in the afternoon

• Almost no evapo-transpiration from the surface,
• A heat flux of 300 W/m2

Advection of humidity
Advection and Radiation
Large-scale vertical velocity
6
A Large-Eddy Simulation
MESO-NH 3D Model Domain size 100km x
100km Resolution 500m 12 hours of simulation
from 6am
Parameterizations 3D turbulence (Deardorff
length scale) microphysics (liquid, ice, rain,
graupel)?
Vertical profiles of temperature and humidity
6h
12h
18h
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
Comparison LES - Observations
Observations
LCL
LFC
BLH
LES
11
Comparison LES - Observations
Observations
CAPE
CIN
LES
12
1D simulations
LMDZ 1D V1 Small-scale turbulence Louis,
1979 shallow and deep convection Emanuel, 1991
MESO-NH 1D Small-scale turbulence TKE
sheme shallow convection Pergaud al.,
2009 deep convection Kain-Fritsch (Bechtold)?
CAPE closure
LMDZ 1D V2 Small-scale turbulence Yamada,
1983 shallow convection Rio Hourdin, 2008 deep
convection Grandpeix Lafore, 2009
same type of boundary layer scheme
MESO-NH 1D LMDZ 1D V1 LMDZ 1D V2
13
1D simulations
MESO-NH 1D LMDZ 1D V1 LMDZ 1D V2
14
1D simulations
Heating rate K/h
15 10 5 0
LES
LMDZ V1
15 10 5 0
height (km)?
height (km)?
8 10 12 14 16 18h
8 10 12 14 16 18h
15 10 5 0
MESO-NH
LMDZ V2
15 10 5 0
height (km)?
height (km)?
8 10 12 14 16 18h
8 10 12 14 16 18h
15
Conclusions and perspectives
10th of July 2006 over Niamey - Unique
system so-well documented with observations -
Unique framework to study processes involved in
the triggering and development of isolated
convective systems in a semi-arid environment
3D high resolution modelling

• Study of processes boundary layer growth,
  shallow clouds, transition from dry to
• cloudy boundary layer, and from shallow to deep
  convection
• - Sensitivity tests to initial profiles,
  large-scale forcings and resolution
• - Surface heterogeneities?

1D modelling
- Ideal case to evaluate hypothesis at the basis
of the parameterizations of boundary layer
turbulence and convection
Particularly how deep convection schemes which
intensity depends on CAPE will behave on such a
case? Representation of transport in the CBL
16
Vertical velocity horizontal cross-section at
600m in LES
at 11am
at 5pm
at 4pm
at 6pm
17
Vertical velocity vertical cross-section in LES
at 11am
at 5pm
at 4pm
at 6pm