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This study evaluates the performance of a dynamically downscaled Weather Research and Forecasting (WRF) model by capturing the characteristics of the interseasonal variability in terms of active and break spells of the Indian summer monsoon during the period 1980–2014. We identify the active and break days based on the standard criteria of previous studies. Further, the composite means in the rainfall and different rainfall events, along with the thermal and dynamical features associated with active and break spells, are analyzed and discussed. Our results clearly show that the WRF model reproduces the observed features of monsoon circulation in active spells such as the wider and intensified lower tropospheric winds, the presence of mid-tropospheric cyclonic circulation, and the dominance of strong upper-level tropical easterlies along with the high influx of moisture towards the Indian subcontinent. Even in the break spells, the WRF model effectively simulates the observed features of the ERA, such as weaker monsoon winds at both low and upper levels and decreased strength of northwesterly winds of Shamal, the presence of a strong thermal inversion over the northwestern part of the Arabian Sea, and a significant increase in the African easterly jet. Moreover, our rainfall analysis during active and break spells reveals that the WRF model accurately reproduces the observed characteristics of the regional-scale precipitation. The results also reveal that the spatial distributions of moderate, heavy, and very heavy rainfall events over the monsoon core region are well captured by the WRF model, with only slight intensity variations compared to the observed distributions.

The synoptic and dynamic characteristics of dust storm events over northern Saudi Arabia were studied during the spring season from 1978 to 2008 using surface dust storm observations from 11 stations and meteorological data from the NCEP/NCAR reanalysis dataset. Two-day dust-free periods were selected before and after each event to represent the pre- and post-event stages, respectively. The synoptic study identified two synoptic systems associated with dust events, i.e., frontal systems and shamal systems, and these systems were associated with increases in the pressure and temperature gradient over the northern Arabian Peninsula (AP) and an eastward shift in the maximum wind as a dust storm event progressed from the pre- to post-event stages. The dynamic study also showed that during the pre-event stage, the atmosphere was baroclinic and featured dynamic disturbances by frontal systems. Additionally, frontal systems resulted in slightly greater intensification than the shamal systems. Moreover, the dynamic study demonstrated that the kinetic energy (KE) shifted eastward and the available potential energy (APE) shifted northward through a series of regions importing and exporting KE and APE. The vertical profile of the average energy area indicated that the main layer in which sensible heat was converted into KE was located above the dust cloud.

Background:The mesoscale circulation over Kuwait is an important influence on changes in surface temperatures and soil temperatures.Introduction:This paper presents two common summertime atmospheric features over Kuwait linking wind circulation to soil temperatures.Methods:In this study, we use the European Centre for Medium-range Weather Forecasts ECMWF reanalysis ERA-Interim dataset to investigate effects of the synoptic scale and mesoscale circulations.Results:The results show that a large-scale pressure gradient in summer typically leads to northerly winds over Kuwait, while a weak synoptic-scale pressure gradient leads to light easterly humid winds from the Persian Gulf, consistent with a mesoscale circulation.Conclusions:The results demonstrate the significance of wind circulations in driving the Soil Temperature (SOILT). Using the Era-Interim/Land reanalysis dataset for August 2015 over Kuwait, the average SOILT on days of sea breeze is higher than the average SOILT on days dominated by a synoptic-scale pressure gradient.

The Akkadian Empire was the first united empire in Mesopotamia and was established at 4.6 kyr B.P. (where present is A.D. 1950). The empire abruptly collapsed in 4.2 ± 0.2 kyr B.P. Seasonal-scale climatic dynamics behind this collapse have not yet been resolved. Here, we present monthly climatic parameters (temperature and hydrology) inferred from fossil Omani corals that lived between 4.5 and 2.9 kyr B.P. Winter temperatures derived from a modern Omani coral correlate with winter shamal (western Asian dust storm) frequency. A fossil coral from 4.1 kyr B.P. shows a prolonged winter shamal season with frequent shamal days. This likely caused agricultural failures in Mesopotamia and contributed to the Akkadian Empire collapse, as this region depends on winter rainfall.

International audience; This study examines the atmospheric circulation patterns that are associated with contrasting wind regimes, desert dust outflows and accumulation of dust over the Arabian Sea in the summer season. The examined period is 11-16 July 2016, when several dust plumes of various intensity and from different sources (Arabian Peninsula, Somalia and Iran), affected the Arabian Sea. During summer, south Asia is under the influence of the southwest monsoon, with main characteristics being the thermal low-pressure system centered over northwest India/Pakistan with secondary lows over south Iran and southeast Arabian Peninsula, and the Arabian ridge combined with the Indian trough in the mid troposphere. Apart from the dominant southwest monsoon flow over the Arabian Sea, strong local winds are developed over the desert areas, such as the northwest Shamal along the east Arabian Peninsula and northern Levar in southeast Iran. These wind regimes initiate several dust outbreaks, while their convergence over the Arabian Sea results in accumulation of large amounts of dust aerosols (AOD > 2.0), as observed by satellite (MODIS, MISR, CALIPSO) observations and reanalysis (MERRA-2). The dust-accumulation area (central/north part of the Arabian Sea) is characterized by weak winds, while the position of the Inter-Tropical Discontinuity (ITD) plays an important role in merging the contrasting dust plumes. The vertical profiles of the monsoon, Shamal and Levar winds are especially important for the dust accumulation, since the low-altitude dust plumes come from the southeastern Arabian Peninsula and Somalia, while those above 3000 m from northern directions (Iran, Pakistan).

This study aims to assess the wind and wave spatio-temporal variability in the Persian Gulf using localized ECMWF wind data and numerically modeled wave characteristics in a 31-yearly period. The results represented that the highest values occur mainly in the middle part of the domain, especially during the winter, and the seasonal variation of the wind and wave climate is mostly affected by Shamal wind phenomena while the winter and summer-time Shamal winds affect the middle and northwestern parts of the Persian Gulf, respectively. For quantitative assessment, twenty stations were selected and the results indicated that the highest mean significant wave height (SWH) occurs in the central strip of the middle parts of the Persian Gulf during both February and June, while the monthly variations of wind and wave characteristics are different in the stations located near the Strait-of-Hormuz. In addition, the temporal stability of both wind speed (WS) and SWH is more in the eastern part of the domain, while the stability of wave dominant direction is more than that of wind. Based on the similarity between the temporal variations of wind and wave characteristics, the domain was divided into three sub-regions as representatives of different wind/wave climates.

Aerosol index (AI) is qualitatively indicating the presence of suspended aerosol particles in the air. The major sources of these particles are desert dust, biomass burning, and volcanic ash plumes. The AI observations derived from the ozone monitoring instrument (OMI) on Aura satellite were analyzed over Iraq for the period 2005–2018. The results showed that the long-term spatiotemporal distribution of AI was significantly variable, with lower values ( 2 may reach more than 140 days in Basra and more than 90 in Anah and Baghdad. Comparisons of Moderate Resolution Imaging Spectroradiometer (MODIS) true color images and AI for five different types of dust storms occurred over Iraq showed that AI is maximum at the core of the storm and the gradation of decreasing AI was consistent with the spread of dust out of the core. Maximum AI was > 5.5 during summer Shamal storm, > 3.0 during winter Shamal and frontal cases, and > 2.0 for the Haboob case. The HYSPLIT trajectories calculations showed that the dust plume in the MODIS image was significantly similar to the computed trajectories and the majority of air masses were coming from north and northwest.

Coniatoids and the more extensive coniatolites were originally described, respectively, as rough surfaced, aragonite coated grains and rough surfaced, aragonite encrusted beachrocks near Jebel Dhanna, Abu Dhabi. At that time, a microbial involvement in their origins was rejected in favour of supratidal physico-chemical precipitation and this study investigates the validity of those conclusions. Vadose aragonite cementation has certainly occurred but new evidence of microbial involvement is presented and an intertidal influence is suggested with due consideration given to Holocene eustatic sea levels. The surface roughness of particularly the coniatolites is largely due to wick-like movement of surface marine waters under the influence of prevailing northwesterly winds, including the Shamal. Leewards growth extensions of the microbial communities in the direction of aeolian-driven, marine surface water drainage were rapidly cemented by micritic aragonite which also engulfed carbonate grains. A similar aeolian wick-like precipitation process is illustrated in a halite deposit of an Abu Dhabi sabkha salina.

Glacially driven eustatic sea-level fluctuations have left a clear signature only along the coastal regions and barrier islands of the Abu Dhabi Emirate. Four marine sequences are identifiable although others are known to exist offshore. The stratigraphy is complicated by aeolian processes associated especially with the Shamal winds which have blown from the northwest to create dune fields that dominate the Quaternary sedimentation. Whilst aeolian facies can clearly be identified separating marine incursions along the coastal regions, aeolian deflation has complicated the stratigraphy by recycling sediment partly in response to loss of windward sediment sources during marine transgressions and partly in response to glacially driven climatic changes. Unravelling the sequence stratigraphy of the desert dunes inland, especially beyond the coastal sabkhas, is therefore extremely difficult. The late Quaternary aeolian dunes and their veneer of mobile aeolian sands are grouped into a single poorly defined formation which spans the entire timescale of the sequences identified along the coast.

The mean annual temperature is 25 °C, with slightly cooler temperatures in the eastern mountains. The mean monthly relative humidity over UAE is around 60% during winter and around 50% during summer, varying between 46% in May to 64% in December. The two wind systems affecting the UAE are the winter “Shamal” winds, which affect the western coast, and the summer monsoon, which affects the Gulf of Oman and eastern mountain areas. The average annual evaporation is 3322 mm, while the mean annual rainfall is 100 mm for the period 1976–2015.

Middle East Area and especially the central part is a dust dominated domain and therefore estimation of natural dust emissions is critical. Aim of this study is to assess the sensitivity of state-of-the art dust modules, utilized in multiple modelling schemes, and especially of their three main components; namely the horizontal mass flux, the drag partition and the sandblasting efficiency. To accomplish this, several simulations with the Natural Emission MOdel (NEMO), driven by the Weather Research and Forecasting (WRF) model, were made for the period April–June 2015 focusing in the central Middle East (CME). First, the meteorological model was evaluated over the study period, as well as during a Shamal event, showing a satisfactory performance on wind speed which is the most important meteorological variable inserted in the dust modules. Second, dust emissions were found to be a few tenths of μg/m2s on average, while the daily amount exceeds 1000 mg/m2day. Over the studied period, the fluxes range from 15 to 750 g/m2. The total emissions in CME were estimated with the NEMO's basic configuration at 139 Tg. The most active areas are associated with clay content ranging between 17 and 25%, highlighting the importance of soil texture on the definition of the dust sources. During a Shamal event in the second half of June 2015, the mean dust emission fluxes reached up to several hundreds of μg/m2s, contributing 21 Tg in CME. Few such events could cover a large portion of the dust emissions. Finally, concerning the sensitivity of the total emissions, the drag partition scheme has the largest effect, followed by sandblasting efficiency and horizontal mass flux. The total dust emissions budget, among the 16 simulations was found to be in the range of 21–139 Tg, with the choice of the drag partition scheme to be mandatory for the narrowing of the total emissions in CME.

Marine areas are affected by different atmospheric phenomena such as wind and storm. In this research the effect of a large scale atmospheric phenomenon, known as Winter Shamal Wind, is investigated on the regime of currents and waves in the northwest part of the Persian Gulf. This wind normally occurs for the period of three to seven days, during December to early March. MIKE21 Coupled Model FM was applied to study the pattern of current and waves for this period. To provide the hydrodynamic data for the model and validate the simulated results, the wind data of ECMWF and mast meteorology of coastal synoptic station of Bushehr and wave data of buoy located offshore of Bushehr was used. The results indicated only a slight increase in current speed with no significant change in current direction during Winter Shamal Wind, showing a stable current pattern in northwest of the Persian Gulf. The significant wave height and wave propagation speed for the period of Winter Shamal Wind in comparison with the days prior to the wind show significant changes. The maximum wave speed in the area under investigation reaches up to 1 m/s and the significant wave height is almost 1 meter higher than that of normal situation.

This study investigates the influence of the Indian Summer Monsoon (ISM) on the atmospheric circulation over the Arabian Peninsula (AP) using the European Centre for Medium Range Weather Forecasts’ twentieth century reanalysis (ERA-20C) for the period 1901–2010. After describing the summer climate of the AP using various dynamic and thermodynamic parameters, we investigate the link between extreme ISMs and atmospheric circulation over the AP on inter-annual time scale. Analysis of composites of different parameters during extreme monsoon (strong and weak) years reveals that the ISM plays an important role in the summer circulation over the AP and adjoining regions. The major noticeable changes in modulating circulation during extreme monsoons are: (1) a strengthening of lower tropospheric northerly winds, westerly winds passing through the Tokar Gap, Shamal winds, and the upper tropospheric easterly jet stream during strong ISM; (2) a northward (southward) shift of the subtropical westerly jet stream during strong (weak) monsoon years; (3) the development of strong upper level ridge above the surface thermal low during strong ISM years, which result in a baroclinic structure over the AP and adjoining regions; (4) an increase in adiabatic warming, and hence aridity, over the AP during strong monsoon years, caused by intense subsidence of the middle to upper troposphere due to zonal overturning circulation; and (5) convective instability during strong monsoon years caused by an intensification of the upward motion over the southern AP. Furthermore, during strong monsoons, the availability of excess moisture leads to atmospheric instability, which in turn triggers the formation of clouds that lead to more rainfall over the southwestern AP. Finally, the westward propagation of a Gill-type Rossby waves induced by the ISM play an important role in the variations of the AP summer climate by enhancing the warm core structure over the AP and through their interaction with the midlatitude westerlies during strong monsoons.

Profiles of periodic GPS Radiosonde ascends collected from a station at the west coast of India (Goa) during summer monsoon months (June to September) of 2009 and 2013 have been used to analyze the thermal inversion statistics at various heights and their repercussions on the regional weather is studied. The interaction of contrasting air masses over the northern Arabian Sea often produces a two layer structure in the lower 5000 m close to the coastal station with warm and dusty air (Summer Shamal) occupying the space above the cool and moist Low Level Jet (LLJ) by virtue of their density differences. The warm air intrusion creates low lapse rate pockets above LLJ and modifies the gravitational stability strong enough to inhibit convection. It is observed that the inversion occurring in the lower 3000 m layer with an optimum layer thickness of 100–200 m has profound influence on the weather beneath it. We demonstrated the validity of the proposed hypothesis by analyzing the collocated data from radiosonde, lidar and the rain gauge during 16th July 2013 as a case study. The lidar depolarization ratio provides evidence to support the two layer structure in the lidar backscatter image. The presence of dust noticed in the two layer interface hints the intrusion of warm air that makes the atmosphere stable enough to suppress convection. The daily rainfall record of 2013 surprisingly coincides with the patterns of a regional break like situation centered at 16th July 2013 in Goa.

The speech of characters is one of the important elements of story as it defines the thoughts of the story and it can promote the events of story. A narrator transfers the speech from the author to the reader and it is manifested as “The narration methods of story speeches”. The story speeches are dived into five groups as direct, indirect, free direct and free indirect and narrative report. In the famous novel “Mawsim al-Hijraila alShamal” by “Tayeb Salih”, contemporary Sudani author, the mentioned methods are manifested based on narrative situation of story. The story is started with the first-person view and the narrator presents the report and other methods are dominant as the characters are increased. The present study is a descriptive-analytic design showing that the direct speech is highly frequent in the novel.

Dust storms are among the most severe environmental problems in arid and semi-arid regions of the world. The predictability of seven dust events, viz. D1: April 2–4, 2014; D2: February 23–24, 2015; D3: April 1–3, 2015; D4: March 26–28, 2016; D5: August 3–5, 2016; D6: March 13–14, 2017 and D7:March 19–21, 2017, are investigated over the Arabian Peninsula using a regionally adapted chemistry transport model CHIMERE coupled with the Weather Research and Forecast (WRF) model. The hourly forecast products of particulate matter concentrations (PM 10 ) and aerosol optical depths (AOD) are compared against both satellite-based (MSG/SEVRI RGB dust, MODIS Deep Blue Aerosol Optical Depth: DB-AOD, Ozone Monitoring Instrument observed UV Aerosol Absorption Index: OMI-AI) and ground-based (AERONET AOD) remote sensing products. The spatial pattern and the time series of the simulations show good agreement with the observations in terms of the dust intensity as well as the spatiotemporal distribution. The causative mechanisms of these dust events are identified by the concurrent analyses of the meteorological data. From these seven storms, five are associated with synoptic scale meteorological processes, such as prefrontal storms (D1 and D7), postfrontal storms of short (D2), and long (D3) duration types, and a summer shamal storm (D6). However, the storms D4 and D6 are partly associated with mesoscale convective type dust episodes known as haboobs. The socio-economic impacts of the dust events have been assessed by estimating the horizontal visibility, air quality index (AQI), and the dust deposition flux (DDF) from the forecasted dust concentrations. During the extreme dust events, the horizontal visibility drops to near-zero values co-occurred with hazardous levels of AQI and extremely high dust deposition flux (250 μg cm − 2 day − 1 ).

This study investigates four types of synoptic dust events in the Middle East region, including cyclonic, pre-frontal, post-frontal and Shamal dust storms. For each of these types, three intense and pervasive dust events are analyzed from a synoptic meteorological and numerical simulation perspective. The performance of 9 operational dust models in forecasting these dust events in the Middle East is qualitatively and quantitatively evaluated against Terra-MODIS observations and AERONET measurements during the dust events. The comparison of model AOD outputs with Terra-MODIS retrievals reveals that despite the significant discrepancies, all models have a relatively acceptable performance in forecasting the AOD patterns in the Middle East. The models enable to represent the high AODs along the dust plumes, although they underestimate them, especially for cyclonic dust storms. In general, the outputs of the NASA-GEOS and DREAM8-MACC models present greater similarity with the satellite and AERONET observations in most of the cases, also exhibiting the highest correlation coefficient, although it is difficult to introduce a single model as the best for all cases. Model AOD predictions over the AERONET stations showed that DREAM8-MACC exhibited the highest R2 of 0.78, followed by NASA_GEOS model (R2 = 0.74), which both initially use MODIS data assimilation. Although the outputs of all models correspond to valid time more than 24 h after the initial time, the effect of data assimilation on increasing the accuracy is important. The different dust emission schemes, soil and vegetation mapping, initial and boundary meteorological conditions and spatial resolution between the models, are the main factors influencing the differences in forecasting the dust AODs in the Middle East.

Waves in the Arabian Gulf (Gulf) are dominated by shamal winds during winter and early summer. Although wave characteristics in the Gulf are broadly studied, features associated with various wind systems are not explicitly covered, especially in the Exclusive Economic Zone (EEZ) of Qatar. In this study, we analyzed the wave parameters measured off Fuwairit, north coast of Qatar during 29 October – 26 November 2019 to identify the features associated with different wind systems. The analyses have been further extended to the Gulf using the reanalysis waves obtained from the COPERNICUS Marine Environment Monitoring Services (CMEMS) to describe the monthly, seasonal and annual characteristics. Results indicate that Nashi winds influence the east and northeast coasts of Qatar with higher waves than those generated by shamal winds. We find exceptional easterly (Nashi) waves during March 2019 contributing to the highest monthly mean Hs, which is a deviation from the known long-term wave climate of the Gulf. This work was jointly carried out under the IRCC International Research Co-Fund Collaboration Program of QU and CSIR-NIO, executed through Office of Research Support (ORS), QU (IRCC-2019-002).

We present a field survey and a number of simulations of the local Persian Gulf tsunami of 19 March 2017 at Bandar Dayyer, Iran, which resulted in one death, five persons missing and significant damage to the port. The field survey defined the inundated area as extending $$\sim\, 40$$ km along the coast, with major effects concentrated on an $$\sim\, 8$$ km stretch immediately west of Dayyer, a maximum run-up of 3 m and maximum inundation reaching 600 m. In the absence of significant earthquakes on that day, we first test the possibility of generation of a landslide; however, our simulations for legitimate sources fail to reproduce the distribution of run-up along the coast. We prefer the model of a meteorological tsunami, triggered by Proudman resonance with a hypothetical weather front moving at 10 m/s in a NNW azimuth, which could be an ancillary phenomenon to a major shamal wind system present over the Persian Gulf on that day. More detailed simulations of the Dayyer tsunami would require an improved bathymetric grid in the vicinity of the relevant coastal segment.

In this paper, a quantitative evaluation of the severe dust storm which occurred in the Middle East during 3–8 July 2009 is presented. The quantification is based on the numerical simulation using the WRF/Chem-D model which has been verified and calibrated for the Middle East region. It is found that, during the 3–8 July 2009 event, more than 9.67 Tg dust were emitted from the study area and the maximum simulated dust emission rate is 540 (μg m −2 s −1 ). The west of Iraq, east of Syria and northwest of Jordan (Al-Nafud desert and western Euphrates alluvial plain) are found to be the most active areas of dust emission, contributing much to the dust emission from the Middle East region. In this study, more that 60% of dust particles were emitted from these areas and less than 10% were emitted from Iran dust sources. About 21% of the deposited dust was deposited in Iran land, while 79% in other parts of the study area. The dust load in the study area was estimated to be more than 0.3 g m −2 . The residence time of dust in the atmosphere was 6.2 days over the study area, 7.8 days over Iran and 6 days over other parts. The simulation results exhibit that Iran contribution in emission rate in the study area is much lower than its contribution in dust deposition and residence time and the conclusion of this study can demonstrate the necessity of forming cooperation for suppressing the severe dust events.

Corals in the Persian/Arabian Gulf are the most thermally tolerant in the world, but live very near the thresholds of their thermal tolerance. Warming sea temperatures associated with climate change have resulted in numerous coral bleaching events regionally since the mid-1990s, but it has been unclear why unusually warm sea temperatures occur some years but not others. Using a combination of 5 years of observed sea-bottom temperatures at three reef sites and a meteorologically linked hydrodynamic model that extends through the past decade, we show that summer sea-bottom temperatures are tightly linked to regional wind regimes, and that strong ‘shamal’ wind events control the occurrence and severity of bleaching. Sea bottom temperatures were primarily controlled by latent heat flux from wind-driven surface evaporation which exceeded 300 W m-2 during shamal winds, double that of typical breeze conditions. Daily temperature change was highly correlated with wind speed, with breeze winds (5 weeks, while the cooler intervening years (2013–2016) had summers with more frequent and/or strong shamal events which repeatedly cooled temperatures below bleaching thresholds for days to weeks, providing corals temporary respite from thermal stress. Using observed data from 2012 onward and simulated data from 2008 to 2011, we show that the severity of bleaching events over the past decade was linked to both the number of cumulative days above bleaching thresholds (rather than total days, which obfuscates the cooling effects of occasional brief shamal events), as well as to maxima. We show that winds of 4 m s-1 represents a critical threshold for whether or not corals cross bleaching threshold temperatures, and provide simulations to forecast sea-bottom temperature change and recovery times under a range of wind conditions. The role that wind-driven cooling may play on coral reefs globally is discussed.

This study investigates the underlying atmospheric dynamics associated with intense dust storms in summer 2018 over the Arabian Peninsula (AP); a major dust source at global scale. It reports, for the first time, on the formation of cyclone over the Empty Quarter Desert as important mechanism for intense dust storms over this source region. The dust direct and semi-direct radiative forcings are observed, for the first time over this source region, using high-resolution in-situ and CERES-SYN satellite observational data. The three-dimensional structure and evolution of the dust storms are inferred from state-of-the-art satellite products such as SEVIRI, AEROIASI and CALIPSO. The dynamics and thermodynamics of the boundary layer during this event are thoroughly analyzed using ERA5 reanalysis and ground based observations. We found that a large dust storm by Shamal winds led up, through radiative forcing, to cyclone development over the Empty Quarter Desert, subsequent dust emissions, development of convective clouds and rain. The cyclogenesis over this region initiated a second intense dust storm which developed and impacted the AP for 3 consecutive days. The uplifted dust by the cyclone reached 5 km in altitude and altered the radiative budget at the surface, inducing both significant warming during night and cooling during day. The dust load uplifted by the cyclone was estimated by the mesoscale model Meso-NH to be in the order of 20 Tg, and the associated aerosol optical depth was higher than 3. The model simulates reasonably the radiative impact of the dust in the shortwave but highly underestimated its impact in the LW. Our study stresses the importance of the dust radiative forcing in the longwave and that it should be accurately accounted for in models to properly represent the impact of dust on the Earth system especially near source areas. Missing the warming effect of dust aerosols would impact both the weather and air quality forecast, and the regional climate projections.

Synthetic Aperture Radar (SAR) in wave mode is a powerful sensor for monitoring the swells propagating across ocean basins. Here, we investigate crossing swells in the Indian Ocean using 10-years Envisat SAR wave mode archive spanning from December 2003 to April 2012. Taking the benefit of the unique “fireworks” analysis on SAR observations, we reconstruct the origins and propagating routes that are associated with crossing swell pools in the Indian Ocean. Besides, three different crossing swell mechanisms are discriminated from space by the comparative analysis between results from “fireworks” and original SAR data: (1) in the mid-ocean basin of the Indian Ocean, two remote southern swells form the crossing swell; (2) wave-current interaction; and, (3) co-existence of remote Southern swell and shamal swell contribute to the crossing swells in the Agulhas Current region and the Arabian Sea.

The occurrence of dust storms in Iran has been a source of interest for centuries, but their study has increased dramatically over the last two decades. This paper reviews recent work on the distribution of dust storms in Iran. We show that the dust events that affect Iran come from sources within the country and also from outside Iran's boundaries. The location of major sources within Iran are identified in high-resolution maps and satellite images. Many of these sources have not been previously identified. This paper discusses the transport pathways of this material, the synoptic conditions associated with dust storms and dust haze, recent changes in dust storm frequencies and their causes, and the consequences of dust storms, particularly with respect to health, for Iranian society. Economic consequences include adverse impacts on solar power generation, crops, productivity of the manufacturing industry, and damage to agricultural land, buildings and infrastructure.

The Middle Eastern Shamal is a strong north-northwesterly wind, capable of lifting dust from the Tigris-Euphrates basin and transporting it to the Persian Gulf and Arabian Peninsula. The present study explores the poorly understood spatial and temporal variability of summer Shamal on the diurnal, seasonal, and interannual time scales, along with its influence on dust storm activity and sensitivity to global patterns of sea surface temperature using a comprehensive set of observational data. Statistics of the summer Shamal season are quantified for the first time, including its onset, termination, duration, and the occurrence of distinct break periods. Based on a multistation criteria, the mean onset and termination of the Shamal season occur on 30 May ± 16 days (1 standard deviation) and 16 August ± 22 days, respectively. Anomalously early (late) onset and termination of the Shamal season are typically associated with La Nina (El Nino) conditions, which favor (inhibit) the development of the Iranian heat low in spring and inhibit (favor) its persistence into late summer. Dust source regions in the Tigris-Euphrates basin and Kuwait, as well as southeastward dust transport during the summer Shamal, which cannot be detected by satellite aerosol products alone, are identified, for the first time, from the Multiangle Imaging Spectroradiometer plume motion vector products and confirmed by surface observations and lidar data. A close interrelationship has been revealed among summertime dust activity across the eastern Arabian Peninsula, frequency of Shamal days, and duration of the Shamal season on the interannual time scales.

Dust and impurity accumulation has a significant effect on the efficiency and performance of PV panel output power. It influences the transmittance of solar radiation from the PV panels surface. Scheduling weekly or monthly cleaning periods requires complete knowledge of area’s weather and environmental condition. In this study, an experimental-based investigation is conducted aiming for a proper scheduling cleaning periods by comparing the output power efficiency of two identical PV panels, the first being cleaned daily and the other cleaned monthly. Both are exposed to unstable weather condition with Sarayat season in April and May, winter and summer Shamal of Kuwait for one year. The results indicated a significant degradation of PV panel output power in April, May, October and December. A need for frequent weekly water washing is a necessity to maintain the power efficiency loss of 15.07%, 13.74%, 10.685% and 8.742% respectively, and frequent monthly water washing for the remaining months of the year.

Ahvaz is among the most polluted cities in the world in terms of particulate matter (PM) concentration. It is a prevailingly vulnerable city to the dust storms intrusion experiencing nearly 98 dusty days per year. The main aim of this study is to determine the transport pathways of dust particles reaching Ahvaz and investigate the dust sources that potentially contribute to dust loading over this city. To this end, temporal and spatial characteristics of Ahvaz dusty days, with a focus on associated air parcel trajectories are investigated in tandem with station observation, potential source contribution function (PSCF) and aerosol optical depth (AOD). Four main dust corridors were identified, based on the trajectory results; one northwesterly and two westerly routes, passing mainly over Tigris Euphrates Plain and Mesopotamian marshlands before hitting Ahvaz. These transport routes are associated with Shamal winds and are active all year long, especially in the summer. Another dust corridor influencing Ahvaz is a southerly route related to the prefrontal dust-storm mechanism. This corridor is active mainly in spring and winter and lifts the dust from Zubair Desert, Ad Dahna Desert and arid land of southern Khuzestan Plain. The forward calculation, PSCF and AOD analysis are consistent with backward air masses trajectory results and showed that eastern Syria, central and southeastern Iraq, and northwest of Ahvaz are the primary sources for dust affecting Ahvaz. Other intense dust sources are located in the south of Ahvaz including the eastern coastal zone of the Arabian Peninsula, southern Iraq, and southeast of Ahvaz.

Anoop, T.R.; Sheela Nair, L.; Prasad, R.; Reji, S.; Ramachandran, K.K.; Prakash, T.N., and Balakrishnan Nair, T.M., 2020. Locally and remotely generated wind waves in the southwestern shelf sea of India. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 77-83. Coconut Creek (Florida), ISSN 0749-0208.The Southwestern Shelf Sea (SWSS) of India has a distinct wave pattern, which makes it different as compared to the adjoining regions. Wave directional spectra during the monsoon season are comparatively broader and double peaked in contrast to that of the western shelf sea. The well-defined directional bi-modality is observed during the south west monsoon which is attributed to the coexistence of the south Indian Ocean swells and the southwest monsoon swells. The shamal swells generated by the shamal wind blowing from the Arabian Peninsula are found to have a significant influence on the wave pattern of the SWSS. In addition, the local sea breeze/land breeze also contributes significantly to the observed changes, particularly to the diurnal variation. A distinct phase lag in occurrence of the maximum significant wave height for the wind sea component is also observed in the northern region of the SWSS during the fair seasons.

Winter Shamals (strong northwesterly winds) are unique surface meteorological phenomena in the Northern Arabian Gulf (NAG). Here we report results from the first observational study designed to investigate the effects of winter Shamals on the hydrodynamics in the NAG. During the Shamal event of 24–26 March 2013, surface wind stress was observed to increase from 0.01 to 0.11 N/m2 and was followed by a decrease in relative humidity from 66.6 to 47.2%. The increase in wind speed and decrease in humidity resulted in a sixfold increase in latent heat loss (from 27.9 to 182.9 W/m2) at the air-sea interface. Such Shamal events were found to affect the hydrodynamics in four aspects: 1. increase of mean surface wave heights and periods, which are fetch limited, from 0.4 to 0.7 m and from 2.8 to 3.8 s, respectively; 2. residual (after removal of tides) surface elevation decrease of 0.6 m and change of residual cross-shore and along-shore velocity fields; 3. Significant increase in turbulent mixing as exemplified by a fivefold increase in mean turbulence kinetic energy dissipation rates from 2.3 × 10−7 to 1.2 × 10−6 W/kg; 4. An almost complete homogenization of the thermal structure.

The interaction of wind and water may well be the key influence on the modern geomorphology of the arid regions of the world, and has had a strong influence on long-term landscape evolution in these areas. This is the case for the landforms of the northern United Arab Emirates, where aeolian landforms in the west lie on alluvial deposits, and are adjacent to fluvial landforms in the east. Even within the aeolian forms there is evidence of modern and past water activity. Modern river flow is rare and largely confined to the mountains. However, rivers and alluvial activity were more important during certain periods in the past. This study describes the landforms of the Northern Emirates (NE) and relates their form and evolution to alternating periods of arid and humid climates. The study was initially carried out to provide a background for the soil survey of the NE. Details of landform character and materials were explored during the survey, which involved detailed site and soil descriptions at 10,020 auger and Geoprobe sites (2 m depth), 200 backhoe pits (2 m depth), and 150 drill observations (10 m depth). The main landforms identified in the study area are the Hajar Mountains, alluvial plains (fans, plains and wadis), dunes (ridges, sand veneer, rising dunes) and coastal forms. The influence of uplift and tilting of the Hajar Mountains during the Miocene and more recently is considered. Sea level changes in the Arabian Gulf are also important. The impacts of past climate change on the evolution of landforms is discussed and related to alternating periods of arid and wet climates. The north-westerly Shamal wind is primarily responsible for the formation and continued evolution of the dune fields seen in the NE today.

The observed climatic controls on springtime and summertime Saudi Arabian dust activities during 1975–2012 are analyzed, leading to development of a seasonal dust prediction model. According to empirical orthogonal function analysis, dust storm frequency exhibits a dominantly homogeneous pattern across Saudi Arabia, with distinct interannual and decadal variability. The previously identified positive trend in remotely sensed aerosol optical depth since 2000 is shown to be a segment of the decadal oscillation in dust activity, according to long-duration station record. Regression and correlation analyses reveal that the interannual variability in Saudi Arabian dust storm frequency is regulated by springtime rainfall across the Arabian Peninsula and summertime Shamal wind intensity. The key drivers of Saudi Arabian dust storm variability are identified. Winter-to-spring La Nina enhances subsequent spring dust activity by decreasing rainfall across the country's primary dust source region, the Rub' al Khali Desert. A relatively cool tropical Indian Ocean favors frequent summer dust storms by producing an anomalously anticyclonic circulation over the central Arabian Peninsula, which enhances the Shamal wind. Decadal variability in Saudi Arabian dust storm frequency is associated with North African rainfall and Sahel vegetation, which regulate African dust emissions and transport to Saudi Arabia. Mediterranean sea surface temperatures (SSTs) also regulate decadal dust variability, likely through their influence on Sahel rainfall and Shamal intensity. Using antecedent-accumulated rainfall over the Arabian Peninsula and North Africa, and Mediterranean SSTs, as low-frequency predictors, and tropical eastern Pacific and tropical Indian Ocean SSTs as high-frequency predictors, Saudi Arabia's seasonal dust activity is well predicted.

Located in the dust belt, the Arabian Peninsula is a major source of atmospheric dust. Frequent dust outbreaks and some 15 to 20 dust storms per year have profound effects on all aspects of human activity and natural processes in this region. To quantify the effect of severe dust events on radiation fluxes and regional climate characteristics, we simulated the storm that occurred from 18 to 20 March 2012 using a regional weather research forecast model fully coupled with the chemistry/aerosol module (WRF–Chem). This storm swept over a remarkably large area affecting the entire Middle East, northeastern Africa, Afghanistan, and Pakistan. It was caused by a southward propagating cold front, and the associated winds activated the dust production in river valleys of the lower Tigris and Euphrates in Iraq; the coastal areas in Kuwait, Iran, and the United Arab Emirates; the Rub al Khali, An Nafud, and Ad Dahna deserts; and along the Red Sea coast on the west side of the Arabian Peninsula. Our simulation results compare well with available ground-based and satellite observations. We estimate the total amount of dust generated by the storm to have reached 94 Mt. Approximately 78% of this dust was deposited within the calculation domain. The Arabian Sea and Persian Gulf received 5.3 Mt and the Red Sea 1.2 Mt of dust. Dust particles bring nutrients to marine ecosystems, which is especially important for the oligotrophic Northern Red Sea. However, their contribution to the nutrient balance in the Red Sea remains largely unknown. By scaling the effect of one storm to the number of dust storms observed annually over the Red Sea, we estimate the annual dust deposition to the Red Sea, associated with major dust storms, to be 6 Mt.

Being in vicinity of vast deserts, the west and southwest of Iran are characterized by high levels of dust events, which have adverse consequences on human health, ecosystems, and environment. Using ground based dataset of dust events in western Iran and NCEP/NCAR reanalysis data, the atmospheric circulation patterns of dust events in the Arabian region and west of Iran are identified. The atmospheric circulation patterns which lead to dust events in the Arabian region and western Iran were classified into two main categories: the Shamal dust events that occurs in warm period of year and the frontal dust events as cold period pattern. In frontal dust events, the western trough or blocking pattern at mid-level leads to frontogenesis, instability, and air uplift at lower levels of troposphere in the southwest of Asia. Non-frontal is other pattern of dust event in the cold period and dust generation are due to the regional circulation systems at the lower level of troposphere. In Shamal wind pattern, the Saudi Arabian anticyclone, Turkmenistan anticyclone, and Zagros thermal low play the key roles in formation of this pattern. Summer and transitional patterns are two sub-categories of summer Shamal wind pattern. In summer trough pattern, the mid-tropospheric trough leads to intensify the surface thermal systems in the Middle East and causes instability and rising of wind speed in the region. In synthetic pattern of Shamal wind and summer trough, dust is created by the impact of a trough in mid-levels of troposphere as well as existing the mentioned regional systems which are contributed in formation of summer Shamal wind pattern.

The 18-year (2000–2017) spatio-temporal distribution of the annual, seasonal and monthly mean wave energy based on the significant height of combined wind waves and swell, mean wave direction and energy wave period are presented using the European Center for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis dataset. Moreover, a new wave energy assessment equation for both shallow and deep waters is derived, which improves the accuracy of the wave energy estimation for various water depths, especially for nearshore shallow water areas. Our detailed analysis results depict that the central parts of the region have a higher level of wave energy potential, especially during the winter, when it is affected by dominant winter-time Shamal wind. The prevailing direction of waves is consistently northwest. The 18-year annual mean results show significant wave heights are found mostly less than 1 m, with annual mean energy densities reaching up to 1.2 kW/m in offshore parts. The wave energy is a higher in the winter and diminishes during spring and summer to reach their lowest values in the fall. Generally, the most and the least abundant wave energy occur in February and September, respectively. The wave energy is mainly arisen due to the energy periods between 2 and 6 s and significant wave heights between 0.5 and 1 m.

Shamal events are extra-tropical weather systems which occur in winter (cold and dry winds) as well as summer (hot and humid winds) with strong northwesterly or northerly winds blowing over the Arabian Peninsula. We have used Weather Research and Forecasting (WRF) model to simulate a major winter shamal event (having duration of 3-5 days), which occurred in 2008 and analyzed the spatial structure and time evolution of shamal winds over the Arabian Sea. The study reveals that horizontally, shamal winds extend upto 14oN and bring out significant changes in the atmospheric temperature longitudinally from Arabian coast to west coast of India; its vertical extension is upto to approximately 8km near Oman and approximately 3km near Ratnagiri coast. Along the Arabian coast a temperature drop of 12oC is observed and along west coast of India a drop of 5oC. It gets dissipated when northeast monsoon winds dominate. Its speed reduces from 15 m/s (Oman coast) to 9m/s (central Arabian Sea) as it propagates into Arabian Sea. As the present work is limited to a case study, the results are not in any way has a Climatological reference.

Major sources of dust in the Middle East have been identified by analyzing the surface meteorological records from weather stations for the period 1998–2003. The geographical distribution, possible sources, and the wind patterns favoring the occurrence of four different types of dust events, i.e. dust-in-suspension, blowing dust, dust storm and severe dust storm, are examined. Four major regions of dust events are found in the study domain. These regions cover Sudan, parts of Saudi Arabia and Iraq, Pakistan, and parts of Iran and Afghanistan. The highest frequency of dust events occurs in Sudan, where the number of dust-in-suspension and severe dust storm is maximum. These events generally occur when north-easterly and north-westerly winds of less than 8 ms −1 prevail. The maximum numbers of blowing dust and dust storm are observed over Iran and Afghanistan as a result of strong north-westerlies, known as Sistan’s 120-day winds. The highest values of mean dust concentration, estimated based on visibility, are found in Pakistan. The region of Saudi Arabia and Iraq are associated with relatively strong wind speeds during dust events that may carry dust particles from the sources. Because the synoptic features responsible for dust emission are different, the peak of the seasonal cycle of dust events occurs in different months of the year in different dust source regions. The major sources of dust are seen in the western parts of the domain during the winter months and shift to the east progressing towards the summer.

[1] Temporal and spatial characteristics of Saudi Arabian dust storms, with focus on associated air parcel trajectories, are investigated using station and gridded weather observations and remotely-sensed aerosol optical depth (AOD). For 13 focal stations, an extensive pool of 84-h backward trajectories is developed for dust storm days, and the trajectories are grouped into 3–5 representative clusters based on the K-means technique and Silhouette Coefficients. Saudi Arabian dust storms are most prominent during February–June, with a mid-winter peak along the southern coast of the Red Sea, spring peak across northern Saudi Arabia around the An Nafud Desert, and early summer peak in eastern Saudi Arabia around the Ad Dahna Desert. Based on backward trajectories, the primary local dust source is the Rub Al Khali Desert and the primary remote sources are the Saharan Desert, for western Saudi Arabia, and Iraqi Deserts, for northern and eastern Saudi Arabia. During February–April, the Mediterranean storm track is active, with passing cyclones and associated cold fronts carrying Saharan dust to Saudi Arabian stations along the northern coast of the Red Sea. Across Saudi Arabia, the highest AOD is achieved during dust storms that originate from the Rub Al Khali and Iraqi Deserts. Most stations are dominated by local dust sources (primarily Rub Al Khali), are characterized by three dominant trajectory paths, and achieve AOD values exceeding 1. In contrast, for stations receiving predominantly remote dust (particularly Saharan), 3–5 trajectory paths emerge and AOD values only reach approximately 0.6 as dust is lost during transport.

The origins of the pre-Debby (2006) mesoscale convective system (MCS) and African easterly wave (AEW) and their precursors were traced back to the southwest Arabian Peninsula, Asir Mountains (AS), and Ethiopian Highlands (EH) in the vicinity of the ITCZ using satellite imagery, GFS analysis data and ARW model. The sources of the convective cloud clusters and vorticity perturbations were attributed to the cyclonic convergence of northeasterly Shamal wind and the Somali jet, especially when the Mediterranean High shifted toward east and the Indian Ocean high strengthened and its associated Somali jet penetrated farther to the north. The cyclonic vorticity perturbations were strengthened by the vorticity stretching associated with convective cloud clusters in the genesis region—southwest Arabian Peninsula. A conceptual model was proposed to explain the genesis of convective cloud clusters and cyclonic vorticity perturbations preceding the pre-Debby (2006) AEW–MCS system.

In order to examine the seasonal characteristics of the dust events over western parts of Iran, surface observations from 27 meteorological stations for the period 1951–2014 were analyzed to obtain spatial distributions and temporal variations and trend of dusty day frequency (DDF). Trends of DDF were analyzed by Mann–Kendall and Sen’s estimator of slope nonparametric statistics. Three meteorological stations were selected in north (Tabriz), middle (Kermanshah), and south of the study area (Ahwaz) as reference stations for detecting the regional differences of DDFs. The results showed that DDF is a variable season by season but in general, DDF increases from north to south and from east to west of Iran. The maximum of DDF is monitored in May, June, and July. There are tangible seasonal increasing–decreasing periods in which these changes are logically related with seasonal changes. Regardless of the existence of the maximum DDF in south and southwest of study area, the most intensive increasing DDF trend is calculated in west middle areas. The most widespread and intensive increasing DDF pattern in west of Iran is observed when it is spring. In this case, the dust storms replaced the rainfalls. Distance from dust sources, major movement ways of dust transporting synoptic systems, regional effective wind activity (such as Shamal wind), and arrangement of high mountains are the known factors affecting frequency variation, distribution, and rate of the trend of all the dust phenomena in west of Iran.

Over the past 22 years, annual mean temperatures have increased by 1°C in Qatar and even greater increases are projected in the future. Since lizards depend on thermoregulation to survive, how do such rises in air temperature affect the Eastern sandfish Scincus mitranus in Qatar? S. mitranus exclusively inhabit Barchan dunes, which are restricted to the South-Eastern region of the country and are currently disappearing due to the North-Westerly Al Shamal winds driving them into the sea. Loss of this ecosystem, coupled with climate change pose serious risk to the survival of S. mitranus. Our study was carried out in two tiers. In the first we set out to estimate dune-dependent population densities, while in the second tier of the study we observed sandfish activity in relation to soil temperature. Sandfish (106) were captured and tagged from 5 terrestrial Barchan dunes in Qatar over a period of 10 months. The captured sandfish ranged from 6 to 29 cm in length and, weighed between 2 and 47 g. Sandfish population estimates were generated for 3 large dunes (Slip face area 1.7 × 104 − 2.5 × 104 m2) and ranged from 30–92 individuals while survival probability ranged from 0.39–0.76 per dune, respectively. Population size (R2 = 0.645) and survival probability (R2 = 0.953) were positively correlated with insect abundance within each dune. Sandfish were observed on the surface of sand dunes at soil temperatures of 35 to 55°C. However sandfish were absent at the mean soil temperature of 44.7°C and present at the mean soil temperature of 43.5°C, a small difference of 1.2°C between the 2 means. Heating of the sandfish significantly affected their ability to carry out activities such as foraging, traveling and interacting. This is the first attempt at creating population baselines and understanding the ecology of S. mitranus in the Barchan dunes of Qatar. Our results may be used to inform environmental management policies in order to preserve this fragile ecosystem.

The results from a∼1 km resolution HYbrid Coordinate Ocean Model (HYCOM), forced by 1/2° Navy Operational Global Atmospheric Prediction System (NOGAPS) atmospheric data, were used in order to study the dynamic response of the Persian Gulf to wintertime shamal forcing. Shamal winds are strong northwesterly winds that occur in the Persian Gulf area behind southeast moving cold fronts. The period from 20 November to 5 December 2004 included a well defined shamal event that lasted 4–5 days. In addition to strong winds (16 m s −1 ) the winter shamal also brought cold dry air ( T a =20 °C, q a =10 g kg −1 ) which led to a net heat loss in excess of 1000 W m −2 by increasing the latent heat flux. This resulted in SST cooling of up to 10 °C most notably in the northern and shallower shelf regions. A sensitivity experiment with a constant specific humidity of q a =15 g kg −1 confirmed that about 38% of net heat loss was due to the air–sea humidity differences. The time integral of SST cooling closely followed the air–sea heat loss, indicating an approximate one-dimensional vertical heat balance. It was found that the shamal induced convective vertical mixing provided a direct mechanism for the erosion of stratification and deepening of the mixed layer by 30 m. The strong wind not only strengthened the circulation in the entire Persian Gulf but also established a northwestward flowing Iranian Coastal Current (ICC, 25–30 cm s −1 ) from the Strait of Hormuz to about 52°E, where it veered offshore. The strongest negative sea level of 25–40 cm was generated in the northernmost portion of the Gulf while the wind setup against the coast of the United Arab Emirates established a positive sea level of 15–30 cm. The transport through the Strait of Hormuz at 56.2°E indicated an enhanced outflow of 0.25 Sv (Sv≡10 6 m 3 s −1 ) during 24 November followed by an equivalent inflow on the next day.

Barchan dune fields are a dominant landscape feature in SE Qatar and a key element of the peninsula&rsquo, s geodiversity. The migration of barchan dunes is mainly controlled by dune size, wind patterns, vegetation cover and human impact. We investigate the variability of dune migration in Qatar over a time period of 50 years using high-resolution satellite and aerial imagery. We then explore its relation to the regional Shamal wind system, teleconnection patterns, and limitations in sand supply associated with the transgression of the Arabian Gulf. Strong size-dependent differences in migration rates of individual dunes as well as significant decadal variability on a dune-field scale are detected, which are found to correlate with the intensity of the North Atlantic Oscillation (NAO) and the Indian Summer Monsoon (ISM), in particular during years of relatively strong (weak) summer Shamals. High uncertainties associated with the extrapolation of migration rates back into the Holocene, however, do not permit further examination of the timing of the loss of sand supply and the onset of the mid-Holocene relative sea-level (RSL) highstand. For the youngest phase considered in this study (2006&ndash, 2015), human impact has likely accelerated dune migration under a weakening Shamal regime through sand mining and excessive vehicle traffic upwind of the core study area.

During the Late Quaternary, the climate of Arabia has fluctuated between periods of higher rainfall and fluvial activity, dominated by the influence of the Indian Ocean Monsoon (IOM) and drier/arid conditions under the influence of the westerlies. This has left a rich legacy of landforms from which temporal and spatial patterns of environmental change are reconstructed. The coastal desert region of the southeastern Arabian Gulf has been a focal point for human settlement since ~ 8000 cal yr BP. The region is strategically located on an important trade route between two ‘cradles of civilization’, namely, Mesopotamia and the Indus. Changes in the evolution and modification of this landscape under varying climatic conditions have influenced humans living in and exploiting this landscape for food and water, raw materials and trade routes. In this study, geomorphological and palaeoenvironmental investigations are integrated to provide a framework of environmental change for the Late Glacial and early–mid Holocene periods against which the archaeology of the area can be set. The Late Glacial and earliest Holocene was characterised by intense aridity and accumulation of mega linear dunes driven by the Shamal winds. In the Arabian Gulf region, this continued into the earliest part of the Holocene, whilst southern Arabia was under the influence of the IOM. The monsoon rains migrated into the Gulf region between 8500–6000 cal BP. During this time, semi-nomadic herders occupied this region and grazing their animals in a landscape covered with C3 savanna grassland. The Neolithic peoples also practised hunting and fishing and the collection of shellfish was an important activity. Pottery shows links with Mesopotamia at this time. From 6000 cal BP the IOM retreated south and rainfall was derived from winterly westerly sources. Under drier conditions a switch occurred to a sparser cover of C4 grasses. From 4500 cal BP the climate became much drier with the development of stronger westerly summer Shamal winds and the reactivation of dunes across the region. An intense arid period occurred at 4100 BP which corresponds with major drought conditions in Mesopotamia and the Indus region, which led to major changes in society. This event occurs at a major transition in the Arabian Gulf Bronze Age archaeological record with a decline in population and trade. The last 4000 yr has largely been characterised by arid conditions similar to those found in the region today.

Using long-term oceanographic surveys and a 3-D hydrodynamic model we show that localized peak winds (known as shamals) cause fluctuation in water current speed and direction, and substantial oscillations in sea-bottom salinity and temperature in the southern Persian/Arabian Gulf. Results also demonstrate that short-term shamal winds have substantial impacts on oceanographic processes along the southern Persian/Arabian Gulf coastline, resulting in formation of large-scale (52 km diameter) eddies extending from the coast of the United Arab Emirates (UAE) to areas near the off-shore islands of Iran. Such eddies likely play an important role in transporting larvae from well-developed reefs of the off-shore islands to the degraded reef systems of the southern Persian/Arabian Gulf, potentially maintaining genetic and ecological connectivity of these geographically distant populations and enabling enhanced recovery of degraded coral communities in the UAE.

The normal surface pressure distribution in the Middle East includes high pressure over the eastern Mediterranean Sea and low pressure over the southeastern Arabian Peninsula. The resulting west-east pressure gradient leads to summertime northerly or northwesterly shamal winds across the Arabian Peninsula, which typically result in many days per month with substantial lofted dust, leading to considerable human health and transportation impacts. It would be helpful to understand how the regional pressure gradient may change in the future, as the strength of this gradient exerts predominant control over the strength of the shamal wind. One factor possibly leading to changes in the strength of the pressure gradient is climate variability. We have simulated the regional climate under a presentday scenario (2006-2010) and a mid-century scenario (2056-2060) using the Weather Research and Forecasting (WRF) model. Our results indicate a weakening of the regional pressure gradient by mid-century, resulting in lower average wind speeds and fewer days conducive to dust storms across the Arabian Peninsula.

Two case studies have been investigated using high-resolution WRF model simulations. The purpose of these case studies is to determine the effects of wind patterns on visibility and aerosol transport in the region. In the first case study, strong synoptic-scale forcing led to a large-scale pressure gradient resulting in strong wind and longrange aerosol transport. In the second case study, the mesoscale land/sea breeze offset weak synoptic-scale forcing near the coast. The daytime sea breeze and nighttime land breeze limited the ventilation of air masses and allowed recirculation of contaminants and aerosols near the shoreline, which may strongly influence visibility and air quality locally.

The sand dunes in Wadi Araba Desert, southwestern Jordan, conform to the influence of two main wind systems: (1) the Shamal “ north wind”, the main determinant of dune patterns, and (2) the southerly winds caused by the Red Sea Trough and Khamasin winds. Wadi Araba is a narrow elongated morphotectonic depression bordered by the high eastern and western mountain ranges that would obstruct most of westerlies in winter and the hot dry easterlies in summer. Wadi Araba Desert is caused by the rain shadow of the eastern and western topographic highs, with an arid–hyperarid climate and moisture index between 0.1 and

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The spatial and temporal characteristics of dust storms in the Middle East were studied by an analysis of the visibility reduction in that region. Eight ‘three-hours’ mean values for each month for a period of 21 years (1973–1993) were used. Data were subjected to cluster analysis of their temporal behaviour. Four main regions were identified and mapped. Stations within each cluster (region) have a similar temporal behaviour different from the behaviour of stations out of that cluster. Sudan, Iraq, Saudi Arabia and the Persian Gulf, are the regions that reported the greatest occurrence of dust storms. Dust storms in Iran, north-eastern Iraq and Syria, the Persian Gulf and southern Arabian Peninsula are more frequent in summer. In western Iraq and Syria, Jordan, Lebanon, northern Israel, northern Arabian Peninsula and southern Egypt they occur mainly in the spring, while in southern Israel and in the Mediterranean parts of northern Egypt, in winter and spring.