The Global Distribution of Mineral Dust

Transcription

1 The Global Distribution of Mineral Dust Ina Tegen Leibniz Institute for f r Tropospheric ric Research, Leipzig, Germany Barcelona, November 07, 2007

2 Dust Effects Role of dust in global climate forcing Role of dust in regional air quality Source: EMEP, 2005 IPCC 2007 Global average radiative forcing Contribution to PM10 (Europe)

3 TOMS AI as Global Dust Indicator Global Dust Models:AEROCOM Median DOT all models NASA Dust source regions: High surface wind speed Low surface roughness, sparse vegetation Availability of fine sediment Low soil moisture aerocomhome.html M. Schulz, LSCE

4 Column and Surface Dust Optical thickness (model) Surface concentration Correlation coefficient (monthly) Remote sensing from satellites gives column information Surface concentration may be uncorrelated to column load

5 Intercontinental Dust Transport North Africa (Sahara) to Europe (e.g., Barkan et al., 2005) Sahara to North America (e.g., Perry et al. 1997) Sahara to Caribbean (e.g., Prospero and Lamb, 2003) Asia to North America (e.g. Sassen et al., 2003) Asia to Greenland (Biscaye et al., 97) South America to Antarctica (Basile et al., 1997 ) Surface concentration Chin et al., ACP,

6 Global Dust Budget Estimates What causes these large discrepancies? Zender et al.,

7 In-Situ Dust Observations Information is sparse near dust source regions Meteorological observations Model surface concentrations Kohfeld,

8 Satellite Remote Sensing e.g. MODIS NASA Kaufman and Stöckli Coarse mode retrieval IPCC 2007 Quantitative retrieval of dust properties over land remains problematic Deep blue retrieval Hsu et al., 2005 NASA

9 AEROCOM Results Kinne, 2005 Agreement in optical thickness does not imply agreement in composition For dust aerosol, initial size distribution is major uncertainty for budget Size distribution differences, same emissions Emission major uncertainty in models, but deposition also important

10 Temporal Changes in Dust Interannual/decadal changes are controlled by climate (and surface modification). Seasonal changes in dust are well characterized, controlled by meteorology and vegetation phenology. Daily timescale is relevant for regional forecast, controlled by meteorology

11 Decadal Changes in Dust Interannual/decadal change in dust concentration strongly controlled by changes in sources. Saharan dust Prospero and Lamb, 2003 Changes in meteorology and surface conditions possible causes. Dust emission Beijing dust weather Gobi dust Dust storm frequency

12 Human Impact on Dust Emissions Impact on soil surfaces by: Anthropogenic Dust of First Kind 1. Direct emission by mechanical impact 2. Wind erosion of disturbed soils Impact on climate: Anthropogenic Dust of Second Kind (Zender et al., 2004) At the global scale, human impact on dust emission is largely unquantified (IPCC 2007: 20% contribution)

13 Dust Emissions from Natural and Cultivated Soils Satellite z 0 ECMWF ERA15 Year 1987 Natural emission 1800 Mt/yr Percent dust from cultivation: ERA15, const. z 0 : 7% ERA15, ERS z 0 : 6% NCEP: 8% 100 Mt/yr Agricultural emission

14 Seasonal Dust Distribution: Model Results DJF MAM JJA SON Layer 1 Dust Mixing Ratio (µg/kg) Tegen et al. (2002) Seasonal changes in dust distribution following seasonal changing weather regimes are well characterized

15 Short-term term Dust Variability Important for forecast: Hourly and daily dust variability Observations role of geostationary satellites?

16 :00 UTC MSG/SEVIRI BTD based dust index (EUMETSAT) red = BTD(12µm,10.8µm) green = BTD(10.8µm,8.7µm) blue = BT(10.8 µm) Kerstin Schepanski Eumetsat 2007 IAMAS 2007 Perugia, 9 th Ju

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32 :00 UTC Kerstin Schepanski Eumetsat 2007 IAMAS 2007 Perugia, 9 th Ju

33 Saharan Dust Source Activation Frequency Saharan Dust source activation (DSA) based on Meteosat-8/SEVIRI 15-min IR dust index retrievals (Schepanski et al., 2007) Schepanski et al., 2007 Tegen et al, 2004 Observations Model Frequency of Emission Events Mismatch of Saharan dust source areas but successful case studies -?

34 Conclusions Dust transport is a global-scale phenomenon, but controlled by small-scale scale regional processes. Intercontinental transport of dust aerosol can be important for regional air quality. Satellite remote sensing improves understanding of dust cycle long term perspective for monitoring? Precise characterization of dust source areas and emission fluxes crucial for studies on climate effects, importance for forecast studies?