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)

0

0.1

0.2

0.3

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)

Cumulated rainfall (m

m x 10)

EOP Ground Based experimental set up

Vertical distributionLIDAR

SégouEOP

BanizoumbouEOP + SOP

Aircraft study area