Department of Geography and Environmental Science Remote sensing of dust in Central Asia using MODIS Deep Blue aerosol optical depth Mohamad Nobakht

Introduction Results

Dust as an aerosol considerably impacts the energy balance of the Frequency of occurrence (FoO) was analyzed in order to localize Earth system via absorption and scattering of radiation in the dust sources. FoO was calculated as the number of days in each atmosphere and through the mechanism by which aerosols season that DOD is greater than 0.2. The units of FoO are modify the optical properties of clouds and land surfaces. Central percentage of days with DOD > 0.2 by total number of days with Asia is a region where large deserts are located in close proximity nonmissing DB AOD data per season. to the mountains whose extensive glaciers and snow packs

provide runoff supporting agriculture in the densely populated foothills (Sorg et al., 2012). Deposition of mineral dust significantly affects glaciers of Tian Shan Mountains in Central

Asia, including both their snow pack and glacier ice (Wake et al., 1994). In this research, spatial distribution and seasonal variations of dust sources in surrounding regions of Tien Shan Mountains are

investigated using satellite remote sensing data obtained between January 2003 and December 2014. 6 7 3 5 4

2 Data & Method 11 1 8

MODIS Deep Blue Products 10 9

Daily satellite images acquired by Moderate Resolution Imaging Spectrometer (MODIS) over a time period of 12 years were

analyzed in order to obtain a map of dust sources in Central Asia. Figure 2. Seasonal variation of FoO distribution for DOD > 0.2 in Central Asia, averaged from 2003 to 2014. Location of the Tian Shan Mountains is indicated by blue polygon and numbered areas in D-J-F The capability of the DB algorithm to provide aerosol properties map indicate the deserts, including Kara Kum (1), Kyzyl Kum (2), Aral Kum (3), Ustyurt Plateau (4), Betpaqdala (5), Saryyesik Atyrau (6), Gurbantunggut (7), Taklimakan (8), Thar Desert (9), Rigestan (10) over bright reflecting deserts in this region allowed a detailed and Atrek Delta (11).

inventory of dust erodible surfaces to be obtained. MODIS DB products used in this study were as follows: Conclusion

• DB AOD at 550 nm over land (Quality Assurance 2 & 3 only) The most recent map of dust sources in Central Asia was • DB Angstrom Exponent Over Land generated using MODIS DB products. Our results are in a good • DB Single Scattering Albedo Over Land at 412 and 650 nm agreement with earlier studies of dust sources in this region and indicate the highest number of dust event days in spring and Methodology summer months. Analysis of FoO distribution revealed that A database of daily dust optical depth (DOD) was generated by sources in east and southern sides of Tian Shan, e.g. Taklimakan imposing two criteria to DB AOD observations (τ): and Gurbantanggut, are the most active sources in spring, while deserts in western Tian Shan, specially Aral Kum and Ustyurt i. Angstrom Exponent less than 0.5 (α < 0.5) Plateau, are the dominant dust sources in summer. In further ii. Decreasing absorption with wavelengths (휔650 − 휔412 > 0) research, the link between these variations and regional climate and also transport route of dust from these desert will be investigated. DOD

References 1. Sorg, A., Bolch, T., Stoffel, M., Solomina, O. & Beniston, M. 2012. Climate change impacts on glaciers and runoff in Tien Shan (Central Asia). Nature Climate Change, 2, 725-731. 2. Wake, C., Mayewski, P., Li, Z., Han, J. & Qin, D. 1994. Modern eolian dust deposition in central Asia. Tellus B, 220-233.

Contact information • Department of Geography and Environmental Science, The University of Reading, Whiteknights, RG6 6AH, Reading, UK. • Email: [email protected] Figure 1. Distribution of τ, α and 휔650 − 휔412 (left) and corresponding DOD (right), for 5 July 2011 over eastern Turkmenistan.