Middle East Deserts Research Articles

Low-Frequency Sweep Design—A Case Study in Middle East Desert Environments

Low-Frequency Sweep Design—A Case Study in Middle East Desert Environments

Natural Aerosols, Gaseous Precursors and Their Impacts in Greece: A Review from the Remote Sensing Perspective

The Mediterranean, and particularly its Eastern basin, is a crossroad of air masses advected from Europe, Asia and Africa. Anthropogenic emissions from its megacities meet over the Eastern Mediterranean, with natural emissions from the Saharan and Middle East deserts, smoke from frequent forest fires, background marine and pollen particles emitted from ocean and vegetation, respectively. This mixture of natural aerosols and gaseous precursors (Short-Lived Climate Forcers—SLCFs in IPCC has short atmospheric residence times but strongly affects radiation and cloud formation, contributing the largest uncertainty to estimates and interpretations of the changing cloud and precipitation patterns across the basin. The SLCFs’ global forcing is comparable in magnitude to that of the long-lived greenhouse gases; however, the local forcing by SLCFs can far exceed those of the long-lived gases, according to the Intergovernmental Panel on Climate Change (IPCC). Monitoring the spatiotemporal distribution of SLCFs using remote sensing techniques is important for understanding their properties along with aging processes and impacts on radiation, clouds, weather and climate. This article reviews the current state of scientific know-how on the properties and trends of SLCFs in the Eastern Mediterranean along with their regional interactions and impacts, depicted by ground- and space-based remote sensing techniques.

Airborne particle radioactivity during desert dust days in Cyprus

Mediterranean countries are often affected by desert dust storms, which have significant effects on the environment and public health. We compared airborne particle radioactivity levels during desert dust and non-dust days in Cyprus.Gross α- and β-radioactivity from Total Suspended Particle (TSP) samples, collected at two urban routine monitoring stations in Limassol and Nicosia, were available for the period 2017–2020 and 2008–2020, respectively. Radionuclides 137Cs and 40K, from TSP samples, were also available from a semi-industrial monitoring station in Nicosia during 2008–2020. Information on desert dust presence, dust origin, particulate matter (PM) levels, and solar activity (KP index and solar sunspot numbers - SSN) were also obtained. We used linear regression models adjusting for seasonality and long-term trends, and solar activity to assess the effect of dust storms on TSP gross α- and β-, and 137Cs and 40K radioactivity levels.Gross α- and β-radioactivity, and 137Cs and 40K radioactivity levels were significantly higher on days with desert dust compared to days characterized with no influence of desert dust. Levels of gross α- and β-radioactivity during dust days were higher when dust originated from the Middle East deserts than from the Sahara Desert. The same trend was observed for the ratios 137Cs to 40K and 137Cs to PM10. Conversely, ratios of TSP gross α- and β-radioactivity to PM10 were significantly lower during desert dust days in comparison to days without dust influence.This study suggests that desert dust increase both TSP gross α- and β-radioactivity, as well as 137Cs and 40K radioactivity levels. Further studies should clarify the contribution of anthropogenic and other natural sources to the emission or transportation of particles radioactivity, to better mitigate future exposures.

Improving the vibrator ground force on unconsolidated ground surfaces in Middle East desert environments

Seismic vibrators have become the preferred sources for land seismic exploration. The objective of the vibrator is to transmit a known and spatially stable source wavelet so that any variations in seismic reflection data can be used to estimate the rock properties and geometries of subsurface geology. Unfortunately, the spatial variation of the ground surface can impact the vibrator performance. Field tests have revealed that the vibrator ground force decreases dramatically on unconsolidated sandy surface conditions, and the effect increases as the vibrator shakes toward high frequencies. A theoretical study is provided to explain this repeatable phenomenon that is independent of vibrator source control systems. Moreover, a practical solution, “BP control,” remedies this reduction in ground force over unconsolidated surfaces, especially sand, by introducing a new effective baseplate weight factor into the vibrator source controller. Field test results illustrate an increase in vibrator ground force at higher-frequency conditions over unconsolidated sand when implementing this new effective baseplate into the vibrator source controller. This increase in ground force may improve the recoverable bandwidth and lead to higher-resolution seismic images when encountering these surface conditions.

Mission profile concept for PV modules: use case – middle east deserts vs temperate European climate

The paper addresses the need to simplify the comparison between different climatic conditions. Therefore, the concept of Mission Profiles is introduced to PV. Mission Profiles are a set of climatic stresses compiled to allow direct comparisons such as temperature, humidity, and UV exposure. The use-case in this paper is a comparison of a temperate with a hot climate. The results show that temperature driven processes are highly accelerated for the hot climate, whereas processes that involve humidity may lead to a similar annual degradation. The impact of light, particularly UV, is even more complex. UV triggered reaction processes can be photon absorption triggered and accelerated by temperature. However, for most observed interactions and material changes UV light goes in conjunction with moisture (H2O) for the chemical reaction and is accelerated by temperature. Calculating the impact of temperature and UV is possible. However, the impact of moisture is almost impossible as it requires the knowledge of the local microclimate. Only a “worst-case” scenario can be assumed while using ambient relative humidity for most events of the day, that, however, do typically not include condensation. With the introduction of Mission Profiles, it should be possible to assess stress more easily for particular sites in general. Differences in mounting such as open rack compared to e.g., BiPV can also better addressed, however, with some assumption to define the microclimate (e.g., exclude rear side cooling).

Identification of typical dust sources in Tarim Basin based on multi-wavelength Raman polarization lidar

Asian mineral dust is one of the main aerosol sources in the Earth–atmosphere system, which generates significant effect on air quality, human health, and climate change. Meanwhile, knowledge of vertical optical properties of dust aerosol is crucially needed for identification of the dust source and improved understanding of radiative effect in climate model. In the study, triple-wavelength polarization Raman lidar observation combined with photometer, radiosonde and simultaneous model data was performed at Kashi in the northwestern of Tarim Basin. Taklimakan desert, located in the center of Tarim Basin, is the largest desert of Asia. Base on the measurement and model, two typical dust sources in different altitude were identified in the study, namely Taklimakan desert (East Road), Central Asia desert and Middle East desert (West Road). Particle size distribution of photometer shows that these cases were all coarse-mode-dominated with effective radius larger than 1.7 μm. The lidar observations revealed particle linear depolarization ratios (PLDR) of the Taklimakan dust ranged from 0.28 to 0.34 at 355 nm, 0.33 to 0.35 at 532 nm and 0.29–0.35 at 1064 nm, while lidar ratios (LR) ranged from 47 to 54 sr at 355 nm and from 42 to 51 sr at 532 nm wavelength. Spectral variation of LR and PLDR for Asian dust and Saharan dust was analyzed. All observed Asian dust present the consistent spectral variation that lidar ratio at 355 nm is higher than that of 532 nm, which however is not the case for Saharan dust. Both Saharan and Asian dust measurement PLDR at 532 nm is larger than that of 355 nm and 1064 nm. The measured dust properties provide particularly valuable information for dust simulation and dust climate model for different dust source.

Enhancing the UV/heat stability of LLDPE irrigation pipes via different stabilizer formulations

AbstractHerein different stabilizer formulations of linear low‐density polyethylene (LLDPE) against UV‐ and heat‐initiated degradation are described. The project aims at outdoor applications, such as irrigation piping and profiles, in the Middle East desert regions, where long‐term weathering stability due to high temperatures and solar radiation is important. Two UV/heat formulations, without and with carbon black (CB) as pigment, were incorporated into LLDPE by melt compounding. Neat LLDPE and the stabilized compounds were exposed to accelerated UV and heat aging. Morphological analysis through scanning electron microscopy of the UV‐exposed neat LLDPE showed more severe surface cracking compared to the CB‐containing LLDPE, while all stabilized compounds did not show any surface degradation. Crack formation was less visible for the thermally aged samples. A significant decrease in molecular weight (MW) was observed for the neat UV‐exposed LLDPE, while both unpigmented stabilized compounds showed little change in MW. Mechanical properties, thermal analysis, and carbonyl index results supported the morphological results, which confirmed that CB alone was slightly more effective in protecting the LLDPE against UV initiated degradation, but performed worse against thermal initiated degradation. UV1 and UV2 compounds were efficient against both UV‐ and heat‐initiated degradation, with UV1 performing better for unpigmented compounds, and UV2 for the pigmented ones.

Safflower (Carthamus tinctorius L.) : Utilisation, genetics and agronomy

Safflower is a deep rooted drought tolerant crop originating from Middle East deserts. It is an ancient but minor crop cultivated for its flowers (for coloring, flavoring foods, dyes, medicinal properties), for seeds (for livestock feed, biofuels and oil) in semiarid and temperate regions. 15 countries are producing safflower in the world where Kazakhstan, USA and Russia are top producers. Its oil is prefered due to higher amount of oleic and linoleic acids contents than any other oil seed crops. Safflower petals have been used for centuries as a spice and medicine in traditional Asian cultures. Safflower is poorly studied for genetics. It is a suitable oil crop for marginal areas with deep roots penetrating to uptake moisture and nutrients leached out of rhizosphere. It is also moderately tolerant to salt stress.

Impact of Dust-Cloud-Radiation-Precipitation Dynamical Feedback on Subseasonal-to-Seasonal Variability of the Asian Summer Monsoon in Global Variable-Resolution Simulations With MPAS-CAM5

In this study, we investigate the effects of increased dust emission from the Middle East deserts on subseasonal-to-seasonal (S2S) variability of the Asian summer monsoon (ASM). Numerical experiments are performed using the Model for Prediction Across Scales (MPAS) coupled with the Community Atmosphere Model (CAM5) physics, with regional refinement at 30 km grid resolution over South Asia and the surrounding regions. Result shows that increased dust emission and transport from the Middle East/West Asia region induces a strong dust-cloud-radiation-precipitation-circulation feedback, resulting in a colder surface over the desert regions and the western Tibetan Plateau, but warmer and moister troposphere with enhanced cloudiness and precipitation over the Pakistan/Northwest India (PNWI) region. The latter changes are amplified by the dust aerosol induced Elevated Heat Pump (EHP) mechanism along the West Himalayas/Iranian Plateau foothill regions, most pronounced during May-June. During July-August, cloud radiation feedback further enhances the warming of the upper troposphere, and cooling of the land surface over the PNWI and adjacent regions over West Asia. The upper tropospheric heating and increased precipitation over PNWI spur a large-scale anomalous Rossby wavetrain and a northward displacement of the subtropical jetstream, manifesting in a contraction of the South Asian High and westward shift of the Western Pacific Subtropical High. As a result, the entire ASM precipitation-cloud system is displaced westward. Precipitation and cloudiness are intensified over northwest and western India and west Asia, but suppressed over southern and central East Asia. Analyses of the S2S variability of the upper level vorticity balance suggests that heating by Middle East dust plays an important role in exciting, and anchoring a teleconnection pattern through interactions among dust-cloud radiation, precipitation heating over the PNWI, the development of an upper level Rossby wavetrain and the northward shift of the boreal summer jetstream over Eurasia.

Modeling the contributions of Northern Hemisphere dust sources to dust outflow from East Asia

Mineral dust aerosols can substantially influence the Earth's climate by altering the radiation budget and modifying cloud microphysical and radiative properties. Through long-range transport, dust aerosols could have a global impact. Here, using a fully coupled meteorology-chemistry model (WRF-Chem) and the tracer-tagging technique, we conduct quasi-global simulations to investigate the characteristics of dust intercontinental transport in the Northern Hemisphere and the source contributions to dust outflow from East Asia. Model results show that total dust emission from the main deserts (i.e., North Africa desert (NFD), Middle East desert (MED) and East Asia desert (EAD)) is about 4531 Tg yr−1, in which 66% is from NFD, 24% is from MED and 10% is from EAD. During long-range transport, the NFD and MED dust plumes are separated into two branches by the Tibetan Plateau, with higher dust concentration of 4 μg m−3 in the northern branch (37° N-60° N). The imported dust mass from NFD and MED to East Asia is 16.0 Tg yr−1 and 33.8 Tg yr−1, respectively; the local dust mass emitted from EAD can circumnavigate and import about 0.41 Tg yr−1 of dust into East Asia. As part of the “Asian outflow”, the MED and NFD dust is transported above 600 hPa with concentration of 2 μg m−3, while the EAD dust is mainly transported below 600 hPa with concentration of 3 μg m−3. The total outflow dust mass from East Asia is 12.0, 9.7 and 7.7 Tg yr−1 from EAD, NFD and MED, respectively. Dust particles dominate the aerosol mass concentration with a fraction of 56.5% in southern East Asia and 75.4% in northern East Asia. Moreover, dust number from EAD dominates the total aerosol number north of 37oN below 600 hPa, with a size range of 0.156–0.625 μm, but the NFD dust number is mainly above 600 hPa. MED dust number dominates the total column aerosol number south of 37 oN, with a size range of 0.312–0.625 μm. Quantifying dust source contributions and the associated dust number loading and size distribution over East Asia is important for understanding the role of East Asian dust outflow in climate and hydrological cycle.

English

Hyoscyamus muticus is an endangered desert plant spread in the Arabian Peninsula and the Middle East deserts. The methanol extract of the aerial parts of H. muticus grown in the arid zones in the Northern regions of Saudi Arabia were subjected to primary phytochemical analysis which revealed the presence of phenolic compounds, flavonoids, tannins and sterols, the gas chromatography-mass spectrometry (GC-MS) analysis of the methanolic extract exhibited different types of phenolic compounds, including ferulic acid, 4-hydroxy-cinamic acid-ester, methyl salicylate and methyl ferulate. The accumulation of phenolic compounds supports the antioxidative properties of the plant against oxidative stress. The antioxidant testing showed that the methanolic extract of H. muticus has a noticeable antioxidant activity with an IC50 of 8.1±0.65 mg/ml and an EC50 of 12.74±1.12 mg/ml. The antimicrobial investigation on 11 microbial strains revealed that the methanolic extract of H. muticus areal parts showed average or weak antibacterial activity against gram-positive bacteria, weak antibacterial activity against gram-negative bacteria and no antifungal activity. Moreover, the investigations exhibited the presence of an antifeedant potential on the methanol extract of H. muticus on the 4th instar larvae of Spodoptera littoralis. Key words: Hyoscyamus muticus, phytochemical analysis, antioxidant capacity, antimicrobial activity, antifeedant assay Spodoptera littoralis.

Biodiversity of fungi in hot desert sands.

The fungal community of six sand samples from Saudi Arabia and Jordan deserts was characterized by culture‐independent analysis via next generation sequencing of the 18S rRNA genes and by culture‐dependent methods followed by sequencing of internal transcribed spacer (ITS) region. By 18S sequencing were identified from 163 to 507 OTUs per sample, with a percentage of fungi ranging from 3.5% to 82.7%. The identified fungal Phyla were Ascomycota, Basal fungi, and Basidiomycota and the most abundant detected classes were Dothideomycetes, Pezizomycetes, and Sordariomycetes. A total of 11 colonies of filamentous fungi were isolated and cultured from six samples, and the ITS sequencing pointed toward five different species of the class Sordariomycetes, belonging to genera Fusarium (F. redolens, F. solani, F. equiseti), Chaetomium (C. madrasense), and Albifimbria (A. terrestris). The results of this study show an unexpectedly large fungal biodiversity in the Middle East desert sand and their possible role and implications on human health.

Origin, Maintenance and Variability of the Asian Tropopause Aerosol Layer (ATAL): The Roles of Monsoon Dynamics

Using NASA MERRA2 daily data, we investigated the origin, maintenance and variability of the Asian Tropopause Aerosol Layer (ATAL) in relation to variations of the Asia Monsoon Anticyclone (AMA) during the summer of 2008. During May-June, abundant quantities of carbon monoxide (CO), carbonaceous aerosols (CA) and dusts are found in the mid- and upper troposphere over India and China, arising from enhanced biomass burning emissions, as well as westerly transport from the Middle East deserts. During July-August, large quantities of dusts transported from the deserts are trapped and accumulate over the southern and eastern foothills of the Tibetan Plateau. Despite strong precipitation washout, ambient CO, CA and dust are lofted by orographically forced deep convection to great elevations, 12–16 km above sea level, via two key pathways over heavily polluted regions: a) the Himalayas-Gangetic Plain, and b) the Sichuan Basin. Upon entering the upper-troposphere-lower-stratosphere, the pollutants are capped by a stable layer near the tropopause, advected and dispersed by the anticyclonic circulation of AMA, forming the ATAL resembling a planetary-scale “double-stem chimney cloud”. The development and variability of the ATAL are strongly linked to the seasonal march and intraseasonal (20–30 days and higher frequency) oscillations of the Asian monsoon.

Erratum to: Investigation of the atmospheric mesoscale circulation patterns and their simulation with WRF-CHEM model of the dust storm occurrence over the southern coast of the Caspian Sea

For the very first time, the mesoscale circulation patterns and synoptic-dynamic structure of the atmospheric systems that led to the dust emission to the south coast region of Caspian Sea (SCRCS) were identified and classified using the region synoptic stations’ observations of 2005–2013. Satellite measurements and images, NCEP/NCAR reanalysis data, and Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-CHEM) model products were also used in this study. Results showed that in 49 % of cases, cyclonic circulations over the Middle East deserts were the main transporter of dust particles into the atmosphere where then transferred to the SCRCS by southerly winds over the Alborz mountains in the lower troposphere and by westerly waves in the middle and upper troposphere. During the warm seasons, the surface heating lead to the development of mesoscale thermal low pressures over the hot deserts on the eastern regions of the Caspian Sea, like Turkmenistan and Qura Qum. Those heat lows were responsible for the 38 % of the occurred events. Turbulence and instabilities in the lower troposphere were identified as the second important dust emitter to the atmosphere where those dust particles transported to the SCRCS with the strong northeasterly wind. The third pattern by 13 % of cases was belonging to the mesoscale thermal low pressure that was developed over the arid regions of Iran like Dasht-e-Kavir. Because of the nature of the turbulence in the lower troposphere and heat lows, the ascent of dust particles by these two mechanisms was limited to a shallow layer in the troposphere. The results of simulation with the WRF-CHEM model, analysis of moderate resolution imaging spectroradiometer (MODIS) images, and spatial zoning of atmospheric optical depth (AOD) confirmed the results of the synoptic study.

Mass distributions and morphological and chemical characterization of urban aerosols in the continental Balkan area (Belgrade).

This work presents characteristics of atmospheric aerosols of urban central Balkans area, using a size-segregated aerosol sampling method, calculation of mass distributions, SEM/EDX characterization, and ICP/MS analysis. Three types of mass distributions were observed: distribution with a pronounced domination of coarse mode, bimodal distribution, and distribution with minimum at 1μm describing the urban aerosol. SEM/EDX analyses have shown morphological difference and variation in the content of elements in samples. EDX spectra demonstrate that particles generally contain the following elements: Al, Ca, K, Fe, Mg, Ni, K, Si, S. Additionally, the presence of As, Br, Sn, and Zn found in air masses from southeast segment points out the anthropogenic activities most probably from mining activities in southeastern part of Serbia. The ratio Al/Si equivalent to the ratio of desert dust was associated with air masses coming from southeastern and southwestern segments, pointing to influences from North Africa and Middle East desert areas whereas the Al/Si ratio in other samples is significantly lower. In several samples, we found high values of aluminum in the nucleation mode. Samples with low share of crustal elements in the coarse mode are collected when Mediterranean air masses prevailed, while high share in the coarse mode was associated with continental air masses that could be one of the approaches for identification of the aerosol origin. Graphical abstract ᅟ.

Amplification of ENSO effects on Indian summer monsoon by absorbing aerosols

In this study, we present observational evidence, based on satellite aerosol measurements and MERRA reanalysis data for the period 1979–2011, indicating that absorbing aerosols can have strong influence on seasonal-to-interannual variability of the Indian summer monsoon rainfall, including amplification of ENSO effects. We find a significant correlation between ENSO (El Nino Southern Oscillation) and aerosol loading in April–May, with La Nina (El Nino) conditions favoring increased (decreased) aerosol accumulation over northern India, with maximum aerosol optical depth over the Arabian Sea and Northwestern India, indicative of strong concentration of dust aerosols transported from West Asia and Middle East deserts. Composite analyses based on a normalized aerosol index (NAI) show that high concentration of aerosol over northern India in April–May is associated with increased moisture transport, enhanced dynamically induced warming of the upper troposphere over the Tibetan Plateau, and enhanced rainfall over northern India and the Himalayan foothills during May–June, followed by a subsequent suppressed monsoon rainfall over all India, consistent with the elevated heat pump (EHP) hypothesis (Lau et al. in Clim Dyn 26:855–864, 2006. doi:10.1007/s00382-006-0114-z). Further analyses from sub-sampling of ENSO years, with normal (<1-σ), and abnormal (>1-σ) NAI over northern India respectively show that the EHP may lead to an amplification of the Indian summer monsoon response to ENSO forcing, particularly with respect to the increased rainfall over the Himalayan foothills, and the warming of the upper troposphere over the Tibetan Plateau. Our results suggest that absorbing aerosol, particular desert dusts can strongly modulate ENSO influence, and possibly play important roles as a feedback agent in climate change in Asian monsoon regions.

Middle East versus Saharan dust extinction-to-backscatter ratios

Abstract. Four years (2010–2013) of observations with polarization lidar and sun/sky photometer at the combined European Aerosol Research Lidar Network (EARLINET) and Aerosol Robotic Network (AERONET) site of Limassol (34.7° N, 33° E), Cyprus, were used to compare extinction-to-backscatter ratios (lidar ratios) for desert dust from Middle East deserts and the Sahara. In an earlier article, we analyzed one case only and found comparably low lidar ratios &lt; 40 sr for Middle East dust. The complex data analysis scheme is presented. The quality of the retrieval is checked within a case study by comparing the results with respective Raman lidar solutions for particle backscatter, extinction, and lidar ratio. The applied combined lidar/photometer retrievals corroborate recent findings regarding the difference between Middle East and Saharan dust lidar ratios. We found values from 43–65 sr with a mean (±standard deviation) of 53 ± 6 sr for Saharan dust and from 33–48 sr with a mean of 41 ± 4 sr for Middle East dust for the wavelength of 532 nm. The presented data analysis, however, also demonstrates the difficulties in identifying the optical properties of dust even during outbreak situations in the presence of complex aerosol mixtures of desert dust, marine particles, fire smoke, and anthropogenic haze.

The adaptive role of nectarial appendages in Colchicum

Within the genus Colchicum of the Colchicaceae family, a small group of species native to the transitional belt of the Mediterranean and the Middle East deserts are characterized by unique morphological traits: nectarial appendages that occur at the base of the perianth segments and consist of two lamellae with teeth. An adaptive advantage to this unique morphological trait has yet to be presented. The morphology of the nectarial appendages was measured in three species and in a population representing a potential new species with similar traits for the first time. Nectarial appendages and nectar standing crop are larger for the inner whorl of perianth segments in all species, although the perianth segments are smaller. Intact flowers received more ant visits in outer than in inner whorl perianth nectaries although they had less nectar; removal of the nectarial appendages resulted in an opposite trend. Ant visits to flowers reduced nectar standing crop. Ant access pattern within flowers and the effect nectarial appendages had on it imply that these organs prevent ant access to nectaries. The negative effect they have on the nectar standing crop could reduce the fitness of the species assuming that ants do not pollinate. The role of nectarial appendages as nectar-theft deterrents is reinforced in light of the group’s harsh habitat and flowering season.

Inter‐annual variability of aerosols and its relationship with regional climate over Indian subcontinent

ABSTRACTThe spatio‐temporal variability of aerosols over Indian subcontinent is mainly due to transported dust from adjacent deserts (Thar and Middle East deserts), local emission due to anthropogenic activities and prevailing meteorological conditions. On large scale, the quantification of transported and locally emitted aerosol from these regions is complicated. Here, we used empirical orthogonal function (EOF) analysis to identify these regions and their variability by using 33 years of Total Ozone Monitoring Spectrometer (TOMS) satellite data. The maximum variability in aerosol is explained by first two EOF modes (70.31 and 20.57%) over Indian subcontinent. The major aerosol, i.e. transported dust from adjacent deserts confined to NW India and Pakistan, is observed in first leading mode, whereas biomass burning, industrial and dense populated region of southeast and eastern region of the Indo‐Gangetic Plain (IGP) are revealed in the second dominant mode. The EOF analysis is carried out specifically for the pre‐monsoon and monsoon seasons over Indian subcontinent as maximum aerosol loading is observed during this period. The region of NW India, IGP, Pakistan and northern Arabian Sea explains maximum variability in both seasons. The first three leading modes and their relationship with different atmospheric and surface variables are carried out for pre‐monsoon and monsoon seasons. This study explains the potential role of aerosols on reduction in cloudiness, increased shortwave at the ground, land‐surface tropospheric warming and its feedback to other related processes. This study strongly suggests that there is a need for further appropriate observational as well as modelling study on the role of semi‐direct aerosol effect over Indian subcontinent.

Dust Events in the Western Parts of Iran and the Relationship with Drought Expansion over the Dust-Source Areas in Iraq and Syria

The most famous deserts exist in subtropical regions which is the direct outcome of insufficient precipitation and high temperatures. The Middle East deserts are subjected often to dust, which reduces horizontal visibility to 5 km, and sometimes even to less than 100 m. The severe and prolong drought recently afflicting the west Asia region has been suggested to be instrumental in producing an increased output of dust into the atmosphere from the region. Regarding the increasing of dust events over the west of Iran with the external origin in the recent decade (from 2000 to present), so the main dust-source areas over Iraq and Syria have been detected using the dust-source map of the southwest of Asia, satellite images and soil type maps. We considered the relationship between the increasing of dust events in the western of Iran and drought expansion over the main dust-production areas during the recent decade. Dust frequency data series, and drought variables which include the VHI (vegetation health index), precipitation and temperature data series in long-term and monthly scales have been monitored and compared. And then we used the correlation analysis that indicated the significant proximity between the dust events and droughts/dryness in a yearly scale and also during the warm season (May to Aug). Meantime the derived results from the T-student test for the aforementioned data series confirm the fact that the droughts are parallel to the increasing of dust events from 1996 to 2011 (especially in the recent decade). We found that the recent droughts in the external dust source areas had the remarkable potential to increase the dust events in the west of Iran.