Benoit Laurent, Béatrice Marticorena, Gilles Bergametti Frequencies and intensities of mineral dust emissions from Chinese and Mongolian deserts: A modeling approach  Benoit Laurent, Béatrice Marticorena, Gilles Bergametti blaurent@lisa.univ-paris12.fr Laboratoire Inter-universitaire des Systèmes Atmosphériques International Symposium on Sand and Dust Storm, Beijing, 12-14 Sept. 2004

Studied area: the main deserts of eastern Asia (35.5°N-47°N; 73°E-125°E)

Dust emissions are sporadic and spatially heterogeneous Dust emission processes Dust emissions are sporadic and spatially heterogeneous soil particle movement: wind friction velocity (U*) > threshold friction velocity (U*t) Saltation Sandblasting Vertical flux F Surface wind Horizontal flux G Main processes of dust production

Emission processes Model outputs Dust emission processes Emission processes Model outputs Erosion threshold Emission frequencies (location and periods) Saltation Emission flux intensities (quantities) Sand-blasting

1- Dust emission frequencies - Erosion threshold Aerodynamic roughness length (Z0) Particle diameter (Dp) Soil moisture Snow cover Surface wind velocity

U*t = f (Dp;Z0) → Determination of Z0 Erosion threshold parameterization U*t = f (Dp;Z0) [Marticorena et al., J.G.R., 1997] For 50 µm < Dp <200 µm (generally always present in arid soils), Z0 is the key parameter to compute dust emission frequencies → Determination of Z0

What are the required input data ? To compute the erosion threshold: - aerodynamic roughness length (Z0) remote sensing 10 m erosion threshold wind velocity ● Dp = 210 µm σ = 1.8 - size-distribution - soil texture: f (depth) FAO ● Soil moisture - precipit., T°, albedo, geopot. ECMWF To compute the emission frequencies we also need: ● Snow cover - snow depth ECMWF ● 10 m wind velocity - surface wind velocity ECMWF

(POLarization and Directionality of the Earth’s Reflectance) Z0 retrieved from the Protrusion Coefficient (PC) Remote sensing: POLDER-1 (POLarization and Directionality of the Earth’s Reflectance) Protrusion Coefficient (PC) derived from POLDER-1 measurements of bidirectional reflectance Empirical relation Z0 = a.exp (PC / b) with a = 4.859.10-3 cm, and b = 0.052 is dimensionless [Marticorena et al., I.J.R.S., 2004] 1 2 3 4 5 6 7 8 9 10 11 12 13 log10(Z0)

Z0 and 10 m erosion threshold wind velocities Z0 map (¼° × ¼°) U*t = f (Dp;Z0) and the neutral vertical wind velocity profile 10 m erosion threshold wind velocity map (¼° × ¼°) m.s-1 Ut(10m) [Laurent et al., J.G.R., submitted]

Z0 and 10 m erosion threshold wind velocities In the Gobi: ● Our results: median ~15 m.s-1 ● Wind velocities associated with dust storms: 11-20 m.s-1 [Natsagdorj et al., Atmos. Env., 2003] ● Wind tunnel and field studies: 10-12 m.s-1 [Murayama, Met. Satell. Cent. Tech. Note, 1988; Hu and Qu, Chin. Meteo. Press, 1997] In the Taklimakan: ● Our results: median ~7 m.s-1 ● Wind velocities associated with dust storms: 6-8 m.s-1 [Wang et al., Water, Air, and Soil Poll., 2003] m.s-1 Ut(10m) [Laurent et al., J.G.R., submitted]

Frequent dust emission areas Simulation of dust emission frequencies (1997-1999) Frequent dust emission areas Longitude Latitude % Dust storm events during 1960-1999 Dust storm occurrences during 1961-2000 [Sun J. et al., J.G.R., 2001] [Sun L. et al., Water, Air, and Soil Poll., 2003]

Seasonal cycle Simulation of dust emission frequencies (1997-1999) Frequencies computed with soil moisture and snow cover [Laurent et al., J.G.R., submitted]

Seasonal cycle Simulation of dust emission frequencies (1997-1999) Frequencies computed with soil moisture and snow cover Frequencies computed with soil moisture and without snow cover Frequencies computed without soil moisture and snow cover [Laurent et al., J.G.R., submitted]

Comparison with TOMS Absorbing Aerosol Index frequencies Simulation of dust emission frequencies (1997-1999) Comparison with TOMS Absorbing Aerosol Index frequencies Location of the most frequent areas [Laurent et al., J.G.R., submitted] In the Taklimakan: Monthly average dust event frequency Monthly average frequency of TOMS AAI > 0.7 r ~ 0.95 slope ~ 0.44 Latitude Longitude Frequencies of significant simulated dust emissions (flux > 10-10 g.cm-2.s-1) Latitude Longitude Frequencies of AAI TOMS > 0.7

2- Dust emission fluxes - Flux parameterization Soil “dry” granulometry % erodible surface

Parameterization of the saltation flux Flux parameterization Parameterization of the saltation flux F= a.G = a.S Srel(Dp).C.U*2(1+U*/U*t (Dp,Z0))(1-U* ²/U*t²(Dp,Z0)) [Marticorena and Bergametti, J.G.R.,1995] Parameterization of the sandblasting efficiency a = f(% clay) [Marticorena and Bergametti, J.G.R.,1995] → Determination of the soil “dry” granulometry

What are the required input data ? - aerodynamic roughness length (Z0) remote sensing 10 m erosion threshold wind velocity ● in-situ measurements - size-distribution - soil texture: f (depth) FAO ● Soil moisture - precipit., T°, albedo, geopot. ECMWF ● Snow cover - snow depth ECMWF ● 10 m wind velocity - surface wind velocity ECMWF To compute the emission fluxes we also need: in-situ measurements Soil “dry” granulometry ● - size-distribution % erodible surface ● - % no cover surface f(Z0)

Sand land east of yellow river Soil “dry” granulometry derived from in-situ measurements Sandy lands Med1(µm) P1(%) s1 Med2(µm) P2(%) s2 Taklimakan 110 100 1,79 - Gurban Tunggut 166 95,6 1,37 348 4,4 2,00 Badain Jaran 196 84,6 1,40 15,4 Tengger 157 89,6 1,30 349 10,4 1,46 Ulan Buh 192 96,8 1,35 3,2 Qubqi 95,7 1,18 4,3 1,93 Sand land east of yellow river 180 83,7 1,25 248 16,3 1,31 Mu Us 243 1,55 Gobi Alluvial- Dunhuang 48 71,5 433 28,5 Alluvial -Yumen 81 86,4 1,85 485 13,6 1,24 Deluvial An'Xi 71 78,5 445 21,5 1,50 Deluvial - Yumen 78 83,4 1,80 479 16,6 Loess Shenmu County, Shaanxi 65 1,28 Sandy Loess Chuanbey, Yulin 74 1,17 Derived from measurements of Gengsheng et al. [Global Alarm: Dust and Sandstorms from the World’s Drylands, report of United Nations, 2001]

Simulated year 1997 1998 1999 Total emissions (106 T) 309 417 426 Simulation of dust emission fluxes (1997-1999) Simulated year 1997 1998 1999 Total emissions (106 T) 309 417 426 106 T Longitude Latitude Mean annual quantity

Seasonal cycle Simulation of dust emission fluxes (1997-1999) In frequency: end of spring In intensity: beginning of spring in 1998

Conclusion Simulations of dust emissions (1997-1999) ● Two main dust emission areas (both in frequency and intensity): the Taklimakan desert in the north western China and the Badain Jaran desert in the northern China ● A pronounced seasonal cycle of dust emissions with a maximum (both in frequency and intensity) in spring ● A weak influence of the soil moisture and the snow cover on simulations of dust emissions ● ~ 400 MT/year dust emitted from eastern Asian deserts

Benoit Laurent, Béatrice Marticorena, Gilles Bergametti Frequencies and intensities of mineral dust emissions from Chinese and Mongolian deserts: A modeling approach  Benoit Laurent, Béatrice Marticorena, Gilles Bergametti blaurent@lisa.univ-paris12.fr Laboratoire Inter-universitaire des Systèmes Atmosphériques International Symposium on Sand and Dust Storm, Beijing, 12-14 Sept. 2004