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J.L. Rajot (1,2), B. Marticorena (2), P. Formenti (2), S. Alfaro (2), B. Chatenet (2), F. Dulac (2,3), K. Desboeufs (2) S. Caquineau (4), M. Maille (2) G. Bergametti (2), A. Gaudichet (2), A.O. Manga (5), A. Diallo (6), L. Menut (2), G. Cautenet (7)(1) Institut de Recherche pour le Développement (IRD), UR 049 ECU, (2) Laboratoire Interuniversitaire des Systèmes Atmosphériques, (LISA), Universités Paris 7-12, (3) Commissariat à l’Energie Atomique, Laboratoire des sciences du Climat et de l’Environnement (LSCE), (4) IRD UR 058 Geotrope, (5) Université A. Moumouni, Niamey Niger, (6) IRD M’Bour, Sénégal, (7) Laboratoire de Météorologie Physique (LaMP), Univ. de Clermont-Ferrand
African Monsoon Multidisciplinary Analysis
MINERAL DUST IN SAHELIAN AFRICA: THE AMMA 2005-2007 FIELD EXPERIMENTLISA
1. How much mineral dust is emitted from the Sahel, and what are the main factors controlling the variability of emissions at various scale ?
2. What are the physico-chemical properties of mineral dust, and how they can be linked to their spectral optical properties and their hygroscopicity?
3. What is the resulting radiative forcing at the regional scale ?
Scientific questions
Optical depth in June 2003 Optical depth in January 2003
• Optical depth in the Sahel are always very high.• Dust emissions are linked to the seasonal cycle of the monsoon.• Their quantification remains questionable specially concerning the effect of human land use (cultivation and breeding), which are expected to increase in the future.
(Chiapello et al., JGR, 1995)
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0.4
0.5
0.6
0.7
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Moyenne 1993-2002
AO
D @
500
nm
SOP1
SOP2
SOP0
Over transport regions such as Cape Verde, the aerosol optical depth is maximum during the wet season, while concentrations at the ground are at their minimum.
Rationale
Experimental strategy In situ ground-based and airborne measurements
Physico-chemical characteristicsValidation of 3D atmospheric models of the dust cycle at two
time-scales:• squall line events (RAMS) - SOP• seasonal and interannual variability (CHIMERE-DUST) -EOP
Evaluation of emissions for the Sahelian area
Spectral optical properties
Radiative forcing
Schedule
2006Special observation periods (SOP) Banizoumbou• February 2006 (during Harmattan period)• May-July 2006 (during Monsoon period)
2005-2007Enhanced observation periods (EOP)M’Bour, Ségou, BanizoumbouM’Bour
EOP
Sampling sites
SAFIRE ATR-42
Inlet AVIRAD / LSCE (Filippi, 2000)allows sampling of supermicron particles
GRIMM
DILUTEURTOPAS
SES
TEOM
GRIMM
DILUTEURTOPAS
SES
TEOM
DILUTEURATTOUI
NEPHELOMETRETSI
AETHALOMETREMagee
TEOM
PM 10
PM2.5
PM 1
AOT, Size distribution,
Cimel sun photometer
Wet and dry deposition
Total deposition
SOP Ground Based experimental set up
Mass concentrationWith PM 10,
2.5 and 1µm inlets
GRIMM optical counterCasacad impactorTEOM / filterDedicated filterDedicated filterDedicated filterNephelometer 3 Aethalometer 7
Number size distributionMass size distributionMass concentrationMineralogyIndividual characteristicsFree iron oxidesDiffusion coefficientAbsorbtion coefficient
Airborne measured parameters
Concentration and composition vs. sizeNumber size distributionIndividual particle characteristics Spectral optical properties (scattering/absorption)
PIP Inlets allow the simultaneous
measurements of mineral aerosol
physico-chemical properties
Hygroscopicity
sequential wet
deposition
scavenged and CCN particles
0
2
4
6
8
10
12
14
03:30 04:30 05:30 06:30 07:30 08:30 09:30
Heure
Vite
sse
du v
ent à
50
cm (
m s
-1)
0
45
90
135
180
225
270
315
360 Dir. vent (°), saltation (cps s-1)
pluie cumulée (m
m x 10)
Vitesse du vent
Direction du vent
Erosion (saltation)
Pluie cumulée
E
S
W
N
In the wet season, dust is emitted by soil erosion due to squall lines.
Cumulated Rainfall
Wind direction
Wind velocity
Time (hh:mn)
Win
d Ve
loci
ty a
t 50
cm h
eigh
t (m
s-1
)
Wind dir. (°), saltation (counts s-1)
Cum
ulated rainfall (mm
x 10)
EOP Ground Based experimental set up
Vertical distributionLIDAR
SégouEOP
BanizoumbouEOP + SOP
Aircraft study area