Study on Dust Storms Climatological Trends, transportation paths and Sources Identification

Content Introduction and Background Methodology Definitions and Indicators Observed Trends of dust storms Diagnosis of causes and identifying sources and hotspots Proposal for observation, monitoring and early warning system for Iraq

LONG-TERM SPATIAL AND TEMPORAL VARIABILITY OF DUST OVER IRAQ Temporal variability of dust episodes and their long-term trends, as well as spatial variability of dust hot spots and sources, are important topics of study In this study we perform a joint analysis of satellite remote sensing data for computing (AOD, AE and NDVI) and horizontal visibility reduction records across Iraq, using the longest data series available in each case.

Two complementary approaches are used to identify regions of high dust loadings and to study seasonal variability and long- term trends of dust Spatial and temporal variability of dust over Iraq using available satellite based observations is presented (MODIS [], MISR[], SeaWiFS [] and MERIS[]). Horizontal visibility observations (Iraqi and Global data ) are used in order to evaluate long-term trends of visibility reductions due to dust episodes.

AOT computed by the Folowing Satellite Sensors MODIS (Moderate-Resolution Imaging Spectroradiometer ) is a payload scientific instrument launched in 1999 on board the Terra(EOS AM) Satellite, and in 2002 on board the Aqua (EOS PM) satellite. The instruments capture data in 36 spectral bands ranging in wavelength from 0.4 µm to 14.4 µm and at varying spatial resolutions (2 bands at 250 m, 5 bands at 500 m and 29 bands at 1 km).payloadTerraEOSAquaµm MISR ( Multi-angle Imaging Spectro Radiometer) is a scientific instrument on the Terra satellite. This device is designed to measure the intensity of solar radiation reflected by the Earth system (planetary surface and atmosphere) in various directions and spectral bands. The MISR instrument consists of an innovative configuration of nine separate digital cameras that gather data in four different spectral bands of the solar spectrum. One camera points toward the nadir, while the others provide forward and aftward view angles at 26.1°, 45.6°, 60.0°, and 70.5°. As the instrument flies overhead, each region of the Earth's surface is successively imaged by all nine cameras in each of four wavelengths (blue, green, red, and near- infrared).Terra satelliteEarthnadirwavelengthsnear- infrared SeaWiFS ( Sea-Viewing Wide-Field-of-View Sensor )was the only scientific instrument on GeoEye's OrbView-2 (AKA SeaStar) satellite. The sensor resolution is 1.1 km (LAC), 4.5 km (GAC). The sensor recorded information in the following optical bands: BandWavelength nm nm nm nm nm nm nm nm.Sea-Viewing Wide-Field-of-View Sensorscientific instrumentGeoEyesatellitesensor resolutionopticalnm MERIS (MEdium Resolution Imaging Spectrometer) is one of the main instruments on board the (ESA)'s Envisat platform. This instrument is composed of five cameras disposed side by side, each equipped with a pushbroom spectrometer provides useful data in 15 spectral bands, generate data that can later be used to create two-dimensional images.Envisatspectrometer

AOD Aerosol Optical Depth (AOD): it depends on the wavelength and represents the vertically- integrated extinction of light by aerosols. AOD, which is a unitless value, provides information about the aerosol amount in the entire column of the atmosphere. The larger the AOD value, the larger the content of aerosols in the column of air

AE Angström Exponent (AE): it is the exponent in the formula that describes the AOD dependency on wavelength. AE is inversely proportional to the size of aerosols, so it is a qualitative indicator of the aerosol particle size of the aerosol present in a given column of air. Desert dust particles are characterized by AE ≤ 0.15 and AOD at 550 nm ≥ 0.15

Normalized Difference Vegetation Index (NDVI): This index indicates whether the area observed by the remote sensor contains green vegetation cover or not. This index is widely used to monitor large variations in vegetation cover and to identify deforestation and desertification processes. NDVI varies between -1 and +1, and it is based on spectral reflectance measurements acquired in the visible (red) and near-infrared regions. Values of NDVI ≤ 0.1 correspond to barren areas of rock, sand, or snow. Moderate values (0.2 to 0.3) represent shrub and grassland. High values (0.6 to 0.8) indicate temperate and tropical rainforests. Monthly and inter-annual climatology of NDVI have been also analyzed in order to detect possible changes in land vegetation cover associated to desertification or changes in land use.

The following MODIS products have been used Monthly averaged MODIS/Terra AOD at 550 nm over land and ocean based on daily measurements. Level 3 data. 1°x1° resolution. March 2000 – April 2013 period. Monthly averaged MODIS/Aqua AOD at 550 nm over land and ocean based on daily measurements. Level 3 data. 1°x1° resolution. July 2002 – June 2013 period. Monthly averaged MODIS/Terra Deep Blue AOD at 550 nm over land based on daily measurements. 1°x1° resolution. Level 3 data. March 2000 – December 2007 period. Monthly averaged MODIS/Aqua Deep Blue AOD at 550 nm over land based on daily measurements. Level 3 data. 1°x1° resolution. July 2002-June 2013 period. Monthly averaged MODIS/Terra Deep Blue Angström exponent over land based on daily measurements. Level 3 data. 1°x1° resolution. March 2000-December 2007 period. Monthly averaged MODIS/Aqua Deep Blue Angström exponent over land based on daily measurements. Level 3 data. 1°x1° resolution. July 2002-June 2013 period. Monthly averaged MODIS/Terra NDVI based on daily measurements. Level 3 data. 1°x1° resolution. March 2000 – April 2013 period.

Angström exponent (AE) and NDVI measurements to compare across them, the period March 2000 – April 2013 was used whenever possible.

Monthly climatology of optical properties of aerosols MODIS/Terra AOD at 550 nm. March 2000 – April 2013

Monthly means of Deep Blue AOD at 550 nm from Terra and Aqua for the period March 2000 – April 2013.

MODIS Deep Blue AOD at 550 nm MODIS/Terra pass over Iraq ≈ 8 UTC MODIS/Aqua pass over Iraq ≈ 10:30 UTC

AOD by different space tools

Means of AOD at 550 nm from MODIS/Aqua for the period Mean of AOD at 550 nm for the period 2008 indicate high dust frequency in this year

Annual means of NDVI from MODIS/Terra for the period

Year to year differences of annual April-May-June-July means of NDVI from MODIS/Terra for the period

Monthly mean variation of MODIS/Terra NDVI for the region limited by lat=[31°N – 36°N], long=[41°E-43°E] (Central Iraq) (a) and of MODIS/Terra NDVI for the region limited by lat=[31- 37N], long=[42E-45E] (Mesopotamian region) (b, after Cuevas, 2013) from July 2002 to April b) a)

Identification of DUST SOURCES By Back trajectories Using HYSPLIT MODEL Statistical analysis using both air mass back-trajectories and AOD measurements is performed in order to identify the extent to which Iraq represents a dust source. Three-dimensional 5-day back trajectories were calculated using the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) version 4 (Draxler and Hess, 1998). The time resolution of these back-trajectories is one hour. Eight sets of back-trajectories were calculated, two for each country capital. The end-points were set at ground level and at 1500 m above see level (a.s.l.) at Kuwait City (Kuwait; °N, °E), Manama (Bahrain; °N, °E), Abu Dahbi (UAE; °N, °E) and Riyadh (Saudi Arabia; °N, °E) for each day within the April-August season in the period , at 12 UTC. For the calculation of back-trajectories, 2.5°x2.5° fields from the National Centers for Environmental Prediction/National Center of Atmospheric Research (NCEP/NCAR) reanalysis meteorological dataset was used.

Three-dimensional 5-day Hysplit 4.0 back-trajectories for each day at 12 UTC within the April-August season in the period , with endpoints at ground level at: a) Kuwait City, b) Manama, c) Abu Dahbi and c) Riyadh. a b c d

Three-dimensional 5-day Hysplit 4.0 back-trajectories for each day at 12 UTC within the April-August season in the period , with endpoints at 1500 m a.s.l. at: a) Kuwait City, b) Manama, c) Abu Dahbi and c) Riyadh. a) ) b) ) c) ) d) )

April to August AOD Weighted Trajectories plot for Kuwait City at surface level, for the period. Major source areas are dark red-shaded. Non-source areas are light blue-shaded. A green cross points the location of Kuwait City.

April to August AOD Weighted Trajectories plot for Kuwait City at 1500 m a.s.l., for the period. Major source areas are dark red-shaded. Non-source areas are light blue-shaded. A green cross points the location of Kuwait City

April to August AOD Weighted Trajectories plot for Manama at surface level, for the period. Major source areas are dark red-shaded. Non-source areas are light blue-shaded. A green cross points the location of Manama.

April to August AOD Weighted Trajectories plot for Manama at 1500 m a.s.l., for the period. Major source areas are dark red-shaded. Non-source areas are light blue-shaded. A green cross points the location of Manama.

Conclusions According to Model Results In general, the AOD Weighted Trajectories analysis performed for Kuwait, Bahrain, UAE and Saudi Arabia for the April to August months within the period shows that: Iraq and desert areas in the northern half of Saudi Arabia followed by Syria and other areas in Saudi Arabia on both its border have dust sources. The identification of spatial and temporal dust and sand sources needs deep study.