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The summertime Sahara and Sahel are the world’s largest source of airborne mineral dust. Cold-pool outflows from moist convection (‘haboobs’) are a dominant source of summertime uplift but are essentially missing in global models, raising major questions on the reliability of climate projections of dust and dust impacts. Here we use convection-permitting simulations of pan-African climate change, which explicitly capture haboobs, to investigate whether this key limitation of global models affects projections. We show that explicit convection is key to capturing the observed summertime maximum of dust-generating winds, which is missed with parameterised convection. Despite this, future climate changes in dust-generating winds are more sensitive to the effects of explicit convection on the wider meteorology than they are to the haboobs themselves, with model differences in the change in dust-generating winds reaching 60% of current values. The results therefore show the importance of improving convection in climate models for dust projections.

On 2 June 2014, a Haboob dust storm occurred in Tehran, which lasted less than 2 h, caused severe damages to the properties and involved loss of human life. This paper describes the behavior of this Haboob dust storm, by analyzing of metrological satellites data, as well as assessing the mesoscale and microscale patterns that led to the occurrence of the dust. A dust detection scheme was developed to monitor the dust formation using the Infrared (IR) channels of the Spinning-Enhanced Visible and Infrared Imager (SEVIRI), carried on board MSG satellites. Restrictive thresholds were placed on the individual components to maximize detection success, and to minimize the misidentification of dust. The results indicated cold and strong downdrafts along with the cold front activity during the maximum temperature over the central hot desert caused a strengthened and intensified wind velocity that led to a strong Haboob in Tehran province. The synoptic analysis indicated that a low-pressure system stretching from the southeast of Iran to the northwest of Iran and Iraq was the dominant feature, despite the presence of a weak high-pressure in the center of Iran. The satellite analysis indicates an extreme dustiness discernible in the southwest of Tehran following the formation of a convective storm; however, uncertainty in dust identification increases as the IR dust signal weakens because of underlying dust cloud beneath the thick convective clouds. The analysis of could physical properties reveals the formation of a convective storm after dramatically decrease in cloud top temperature (CTT) and cloud top pressure (CTP), and increasing the cloud optical depth (COT) which led to development of an overshooting cold cloud over Tehran province before dust formation.

Dust storms, such as those associated with haboobs and strong regional winds, are frequently assumed to cause increases in cases of Valley fever (coccidioidomycosis). The disease is caused by inhaling arthroconidia of Coccidioides fungi that, after being disturbed from semi‐desert subsoil, have become airborne. Fungal arthroconidia can be transported in low‐wind conditions as well as in individual dust events, but there is no reliable evidence that all or most dust storms consistently lead to subsequent increases in coccidioidomycosis cases. Following a review of the relevant literature, this study examines the relationship between dust storms and coccidioidomycosis cases to determine if there is a consistent and general association between them. All recorded dust storms from 2006 to 2020 in and near the Phoenix area of Maricopa County, Arizona and the Bakersfield area of Kern County, California were used in a compositing analysis (superposed epoch analysis) of subsequent coccidioidomycosis cases in each area. Analyses of monthly and weekly disease case data showed no statistical differences in the patterns of coccidioidomycosis cases following dust storms versus non‐dust storm conditions, for the entire data set as well as for seasonal subsets of the data. This study thoroughly analyzes post‐dust storm coccidioidomycosis cases for a large set of dust storms, and it confirms and expands upon previous literature, including a recent study that measured airborne arthroconidia and found no consistent links connecting wind and dust conditions to increases in coccidioidomycosis., Key Points It is often asserted that large dust storms like haboobs generally lead to increases in cases of Valley fever (coccidioidomycosis)This study thoroughly tests that assertion using dust storm and coccidioidomycosis case data over many yearsConsistent with literature, results show no statistical difference in cases of the disease after dust storm and non‐dust‐storm conditions

The Saharan Air Layer (SAL) is known as an elevated, well-mixed, warm, dry, frequently dusty layer and plays an important role in regional climate and dust transport. A new analysis of aircraft observations of haboob-driven dust events shows that although increased dustiness in the SAL is associated with drier conditions in the lower-SAL as expected, dustiness is also associated with increased moisture in the upper-SAL, likely originating from cold pool outflows driving the dust uplift. We assess the radiative effects of the observed dust and increased water vapor (WV). The observed WV in the upper-SAL affects the top-of-atmosphere (TOA) direct radiative effect (DRE), while lower-SAL WV affects the surface DRE and column atmospheric heating. TOA DRE is negative for dust-only, while including both the observed dust and WV reduces the magnitude of the negative TOA DRE by 17% (3.0±0.8 Wm-2) when AOD>0.6. The observed WV structure increases the magnitude of the negative surface DRE from dust by 8% (5.1±0.8 Wm-2) and increases atmospheric heating by 17% (8.0±0.6 Wm-2). These effects are driven by longwave (LW) radiation, whereby WV changes increase the positive TOA LW DRE, decrease the surface LW DRE and change the sign of LW atmospheric heating from negative to positive. WV leads to enhanced cooling in the moist upper-SAL and heating in the dry lower-SAL under dustier conditions. Increased WV in the SAL is consistent with other studies demonstrating increasing Saharan WV. This work demonstrates the importance of upper-SAL WV in determining the radiative effect of dust.

This study characterizes a massive African dust intrusion into the Caribbean Basin and southern US in June 2020, which is nicknamed the “Godzilla” dust plume, using a comprehensive set of satellite and ground-based observations (including MODIS, CALIOP, SEVIRI, AERONET, and EPA Air Quality network) and the NASA GEOS global aerosol transport model. The MODIS data record registered this massive dust intrusion event as the most intense episode over the past 2 decades. During this event, the aerosol optical depth (AOD) observed by AERONET and MODIS peaked at 3.5 off the coast of West Africa and 1.8 in the Caribbean Basin. CALIOP observations show that the top of the dust plume reached altitudes of 6–8 km in West Africa and descended to about 4 km altitude over the Caribbean Basin and 2 km over the US Gulf of Mexico coast. The dust intrusion event degraded the air quality in Puerto Rico to a hazardous level, with maximum daily PM10 concentration of 453 µg m−3 recorded on 23 June. The dust intrusion into the US raised the PM2.5 concentration on 27 June to a level exceeding the EPA air quality standard in about 40 % of the stations in the southern US. Satellite observations reveal that dust emissions from convection-generated haboobs and other sources in West Africa were large albeit not extreme on a daily basis. However, the anomalous strength and northern shift of the North Atlantic Subtropical High (NASH) together with the Azores low formed a closed circulation pattern that allowed for accumulation of the dust near the African coast for about 4 d. When the NASH was weakened and wandered back to the south, the dust outflow region was dominated by a strong African easterly jet that rapidly transported the accumulated dust from the coastal region toward the Caribbean Basin, resulting in the record-breaking African dust intrusion. In comparison to satellite observations, the GEOS model reproduced the MODIS observed tracks of the meandering dust plume well as it was carried by the wind systems. However, the model substantially underestimated dust emissions from haboobs and did not lift up enough dust to the middle troposphere for ensuing long-range transport. Consequently, the model largely missed the satellite-observed elevated dust plume along the cross-ocean track and underestimated the dust intrusion into the Caribbean Basin by a factor of more than 4. Modeling improvements need to focus on developing more realistic representations of moist convection, haboobs, and the vertical transport of dust.

Haboob occurrence strongly impacts the annual variability of airborne desert dust in North Africa. In fact, more dust is raised from erodible surfaces in the early summer (monsoon) season when deep convective storms are common but soil moisture and vegetation cover are low. On 27 June 2018, a large dust storm is initiated over North Africa associated with an intensive westward dust transport. Far away from emission sources, dust is transported over the Atlantic for the long distance. Dust plume is emitted by a strong surface wind and further becomes a type of haboob when it merges with the southwestward deep convective system in central Mali at 0200 UTC (27 June). We use satellite observations to describe and estimate the dust mass concentration during the event. Approximately 93% of emitted dust is removed the dry deposition from the atmosphere between sources (10°N–25°N; 1°W–8°E) and the African coast (6°N–21°N; 16°W–10°W). The convective cold pool has induced large economic and healthy damages, and death of animals in the northeastern side of Senegal. ERA5 reanalysis has shown that the convective mesoscale impacts strongly the climatological location of the Saharan heat low (SHL).

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.

On the evening of May 02, 2018, an unusually severe dust storm (DS) from a convective system, which developed over the Thar Desert, struck northwest India resulting in more than 100 casualties. Analysis of its genesis from surface measurements and reanalysis data indicates that this DS was �Haboob� type which are formed when strong downdrafts from a convective system reaches the surface in arid regions. Surface observations show that this DS was accompanied by a sharp drop in temperature and visibility and increase in relative humidity. Model simulation at convective-permitting scale reveals the complex structure of dust transport in space and time. In contrast to the generally observed dust storms over the Indo-Gangetic Plain being mostly associated with westerly wind bringing dust from Southwest Asia and Eastern Africa, this particular DS was triggered by strong easterly wind. The moisture-laden easterly wind at the surface level colliding against the dry westerlies from the desert region along a steep front resulted in strong convection over northwest India leading to the formation of strong downdrafts. This, in turn, was largely due to the positioning of the upper level jet stream, which modulated the location and the strengths of surface lows and highs. The importance of this study is that while recent studies indicate that dust aerosol over India is on the decline partly due to reduction in westerly wind strength, the present work shows that anomalous easterlies can provide an alternate pathway to intense dust storms over the region. © 2021. American Geophysical Union. All Rights Reserved.

This study characterizes a massive African dust intrusion into the Caribbean Basin and southern U.S. in June 2020, which is nicknamed the Godzilla dust plume, using a comprehensive set of satellite and ground-based observations (including MODIS, CALIOP, SEVIRI, AERONET, and EPA Air Quality network) and the NASA GEOS global aerosol transport model. The MODIS data record registered this massive dust intrusion event as the most intense episode over the past two decades. During this event, the aerosol optical depth observed by AERONET and MODIS peaked at 3.5 off the coast of West Africa and 1.8 in the Caribbean Basin. CALIOP observations show that the top of dust plume reached altitudes of 6–8 km in West Africa and descended to about 4 km altitude over the Caribbean Basin and 2 km over the U.S. Gulf coast. The dust plume degraded the air quality in Puerto Rico to the hazardous level, with maximum daily PM10 concentration of 453 μg m−3 recorded on June 23. The dust intrusion into the U.S. raised the PM2.5 concentration on June 27 to a level exceeding the EPA air quality standard in about 40 % of the stations in the southern U.S. Satellite observations reveal that dust emissions from convection-generated haboobs and other sources in West Africa were large albeit not extreme on a daily basis. However, the anomalous strength and northern shift of the North Atlantic Subtropical High (NASH) together with the Azores low formed a closed circulation pattern that allowed for accumulation of the dust near the African coast for about four days. When the NASH was weakened and wandered back to south, the dust outflow region was dominated by a strong African Easterly Jet that rapidly transported the accumulated dust from the coastal region toward the Caribbean Basin, resulting in the record-breaking African dust intrusion. In comparison to satellite observations, the GEOS model well reproduced the MODIS observed tracks of the meandering dust plume as it was carried by the wind systems. However, the model substantially underestimated dust emissions from haboobs and did not lift up enough dust to the middle troposphere for ensuing long-range transport. Consequently, the model largely missed the satellite-observed elevated dust plume along the cross-ocean track and underestimated the dust intrusion into the Caribbean Basin by a factor of more than 4. Modeling improvements need to focus on developing more realistic representations of moist convection, haboobs, and the vertical transport of dust.

Cold pool outflows (CPOs) are thought to be the most significant meteorological mechanism of mineral dust emission from the world's largest source in the central and western Sahara in boreal summer. An absence of CPOs from numerical models and reanalyses used to simulate Saharan dust emission leads to considerable error in modeling of dust fluxes from the Sahara. As such, the role of CPOs in the observed variability of dust through the monsoon season remains unclear. To remedy these issues, an improved observational benchmark is needed. In this research, an automated approach to identify and track CPOs in dust imagery from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) is derived. The approach is found to flag 74.2% of events identified manually (26/35). 1,559 events are tracked for June, July and August of 2004–2017. CPOs follow a clear diurnal cycle, peaking at 1700–1900 Universal Time Coordinated. Propagation speeds decay exponentially through their lifetime, but on average speeds are 1.5 ms−1 higher at night. About 22.5% of the observed events exceed a total traveled distance of 300 km, with an overwhelming preference for northwestwards propagation. Common across the southern central and western Sahara, CPO activity shifts north through summer in line with observed dust emission. The exception to this is the development of an intense hotspot of CPO activity in southern Algeria in August, which does not parallel any known late season outbreaks of dust. The results underline the importance of the southernmost Saharan dust sources, activated by frequent CPO occurrence in early summer.

International audience; We present a new characterisation of the three-dimensional (3D) distribution of dust over the Sahara during summer, exemplified for June 2011. Our approach, called AEROIASI, is based on the innovative retrieval of vertical profiles of the dust extinction coefficient from daily cloud-free hyperspectral Infrared Atmospheric Sounder Interferometer (IASI) satellite observations. AEROIASI observations clearly agree with other widely used measurements (from lidar and radiometers). The 3D charac-terisation is focused on the dust maximum in June 2011, located in the central Sahara (17-23 • N, 1-7 • E) and linked to the major atmospheric dynamical drivers associated with the West African Monsoon (WAM) system. AEROIASI shows the near-surface dust load to be dominated by five major emission events occurring every 3-4 days. These all occur when the study region is under the influence of northward bursts of the WAM and convection-related cold pools, likely associated with orographic forcing by the Aïr Mountains. During the earliest (June 10) and the dustiest (June 17) cases, northward advection of moisture over the hotspot is favoured by the super-position of cyclonic circulations related to an extratropical disturbance northwest of the Sahara and to the Saharan heat low over Mauritania, respectively. Convec-tion over the hotspot also triggers wave-like disturbances that travel westwards. The three dustiest events are characterised by elongated dust fronts moving northwards, with a leading edge spanning 200-300 km horizontally and extending from the surface up to 2 km of altitude. Further south, the dust layer progressively elevates to 3.5 km along the slanted isentropes at the interface of the monsoon and the har-mattan, increasingly losing contact with the ground. When northerlies blow over the study region, elevated dust layers at 3-5 km are observed, which are transported southwards within the Saharan air layer and westwards along the northern edge of the African easterly jet (after June 13). K E Y W O R D S cold pools, dust vertical profile, haboobs, West African monsoon bursts Q J R Meteorol Soc. 2020;1-25. wileyonlinelibrary.com/journal/qj

Dust events are important geomorphological phenomena in many of the world’s dry lands and four main types can be defined: dust storms, dust haze, blowing dust and dust devils. This paper is concerned with the first two of these categories. Methods for their investigation include the examination of terrestrially observed meteorological data, remote sensing, and deep-sea core sediments. Meteorological data are widely available, but care needs to be exercised in their use. Three main types of remote sensing platforms have proved to be useful: geostationary meteorological satellites, polar orbiting satellites, and the space shuttle orbiters. The deep-sea record provides a long sequence of deposition and helps in the identification of major sinks. Combining the data from these three sources, the major locations of dust storm activity can be identified. However, dust storm frequencies are prone to variation from year to year, and land-use and climatic changes can substantially affect their occurrence. Among important controls of the distributional pattern are the meteorological conditions that entrain dust, including low pressure fronts with intense baroclinal gradients, the convergence zone between cold air masses in regions of monsoonal airflow, katabatic winds, and local convectional cells (haboobs). Another major control is the nature of the surface upon which deflational activity works.

Blowing dust events are a common feature of life in West Texas and the Southwestern United States and are increasing in frequency. The composition of inhaled air varies from region to region and may include harmful particles, such as particulate matter, bacteria, fungi, and viruses. There are several types of blowing dust events that can be characterized by physical observations, including the source of dust, the direction of the wind, the density of the particulate matter, and several other physical parameters. All blowing dust events have the potential to cause adverse health effects. Inhalation of dust can cause direct respiratory effects that range from transient cough to acute fungal infection to acute respiratory failure. Asian dust storms increase all-cause and respiratory disease emergency room visits and pneumonia admissions. There is an association between meningococcal meningitis and Saharan dust storm intrusions into West Africa. Haboob (Arabic for strong wind) dust storms stir up large amounts of dust from the environment and can blow it into densely populated areas. The “haboob lung syndrome” has been reported in patients from West Texas who presented with dusty sputum, sterile cultures, and multilobar infiltrates. Some of these patients required admission to the hospital for acute respiratory failure and mechanical ventilation. Blowing dust events are a serious public health issue that can be avoided with prevention. Therefore, it is important to forecast blowing dust events and to get this information out to the public on days with an increase in particulate density. The population can benefit from these warnings by simply wearing a respirator mask on these days and by avoiding unnecessary trips outside.

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 research provides a comprehensive long term time series analysis of the spatiotemporal variability of aerosol optical depth (AOD) over the United Arab Emirates (UAE) using MODIS (Moderate-resolution imaging spectroradiometer) MAIAC (Multi-Angle Implementation of Atmospheric Correction) AOD (aerosol optical depth) product for the period 2003–2018. The UAE is located in one of the driest places on earth, the Arabian Peninsula, with two large extended desert regions that form major atmospheric dust sources in the world. The atmospheric dust emitted by these vast deserts is transported locally and regionally and it is the primary major contributor to the overall aerosol optical depth in this area. The investigation of the spatiotemporal trends of AOD over the UAE showed a significant obvious annual seasonal variability. Results showed a significant increase in AOD during summer due to high wind speed, resulting in scattered events of small to large scale haboobs within the study area, high temperature, and high relative humidity. The increased humidity levels are due to increased temperatures in the summer season leading to significant evaporation from the neighbouring water bodies (mainly the Arabian Gulf and the Sea of Oman) leading to a significant increase in water vapour levels in the atmosphere. Summar AOD values during the study period ranged between 0.42 – 0.73. The second highest AOD was observed in spring followed by winter. Spring AOD values ranged between 0.33-0.58 and winter values ranged between 0.25 – 0.41. The spatial distributions of AOD showed higher values over the coastal and desert areas. Coastal areas portrayed higher values as well likely due to the high levels of evaporation and increased anthropogenic activities such as coastal urban developments and automobile pollution. Time series analysis of the multitemporal dataset confirmed the SARIMA forecast model as the best fit which can be used to provide an accurate and reliable monthly forecast for the AOD concentrations in the UAE.

Convective dust storms have significant impacts on atmospheric conditions and air quality and are a major source of dust uplift in summertime. However, regional-to-global models generally do not accurately simulate these storms, a limitation that can be attributed to (1) using a single mean value for wind speed per grid box, i.e., not accounting for subgrid wind variability and (2) using convective parametrizations that poorly simulate cold pool outflows. This study aims to improve the simulation of convective dust storms by tackling these two issues. Specifically, we incorporate a probability distribution function for surface wind in each grid box to account for subgrid wind variability due to dry and moist convection. Furthermore, we use lightning assimilation to increase the accuracy of the convective parameterization and simulated cold pool outflows. This updated model framework is used to simulate a massive convective dust storm that hit Phoenix, AZ, on 6 July 2011. The results show that lightning assimilation provides a more realistic simulation of precipitation features, including timing and location, and the resulting cold pool outflows that generated the dust storm. When those results are combined with a dust model that accounts for subgrid wind variability, the prediction of dust uplift and concentrations are considerably improved compared to the default model results. This modeling framework could potentially improve the simulation of convective dust storms in global models, regional climate simulations, and retrospective air quality studies.

In 1917, T. E. Lawrence recorded his experience of the passage of a dust storm, or haboob, while travelling in Hejaz in Arabia. The account was published that year in The Arab Bulletin, an intelligence journal. The description of this encounter is vivid, and it is sufficiently detailed that it allows comparison with more recent scientific investigations of the phenomena described. These storms are still subjects of research, which is aimed at improving representation of their weather- and climate-related effects.

Meso-scale weather systems, such as convective haboobs, are considered to be an important dust generation mechanism. In Israel, however, rather than of meso-scale weather systems, most dust storms are generated by synoptic-scale systems, originating from Sahara and Arabia. Consequently, only distal sources of suspended and deposited dust in Israel are currently reported. Here we report the first detailed study on the merging of synoptic- and meso-scale weather systems leading to a prominent dust outbreak over the Negev, Israel. During the afternoon of May 2 nd , 2007, a massive dust storm covered the northern Negev, forming a one kilometer high wall of dust. The haboob was associated with PM 10 concentrations of 1000–1500 μg m −3 that advanced at a speed of 10–15 m s −1 and caused temporary closure of local airports. In contrast to most reported haboobs, this one was generated by a sea breeze front acting as a weak cold front enhanced by a cold core cyclone positioned over Libya and Egypt. The sea breeze that brought cold and moist marine air acted as a gravity current with strong surface winds. The sources for the haboob were the loessial soils of the northwestern Negev, especially agricultural fields that were highly disturbed in late spring to early summer. Such surface disturbance is caused by agricultural and/or intensive grazing practices. Our study emphasizes the importance of local dust sources in the Negev and stresses loess recycling as an important process in contemporary dust storms over Israel.

Dust storms known as ‘haboobs’ occur in Tempe, AZ during the North American monsoon season. This work presents a catalog of haboob occurrence over the time period 2005–2014. A classification method based on meteorological and air quality measurements is described. The major factors that distinguish haboobs events from other dust events and from background conditions are event minimum visibility, maximum wind or gust speed, and maximum PM10 (particulate matter with aerodynamic diameters of 10 μm or less) concentration. We identified from 3 to 20 haboob events per year over the period from 2005 to 2014. The calculated annual TSP (total suspended particulate) dry deposition ranged from a low of 259 kg ha−1 in 2010 to a high of 2950 kg ha−1 in 2011 with a mean of 950 kg ha−1 yr−1. The deposition of large particles (PM>10) is greater than the deposition of PM10. The TSP dry deposition during haboobs is estimated to contribute 74% of the total particulate mass deposited in Tempe.

Severe weather, which is a regular occurrence in the American Southwest, includes more than high temperatures and haboobs (dust storms). Severe thunderstorms, often accompanied by high winds and hail, are regularly experienced and have the potential to cause damage to roofing systems and other exterior building components. Insurance claims for storm damage — both legitimate and unwarranted — have come under increased scrutiny due to indistinct and altered dates of loss, the amending and broadening of damage causes, and the offering of technically unsupportable opinions by individuals who are less than qualified. Further, these claims often end in appraisal hearings that are decided by umpires for whom there are no minimum educational or experiential requirements.

The local strong sandstorms (LSS), similar to haboobs in Sahara and the North America, often occur suddenly, in tens of minutes during the late afternoon, and before dusk in deserts in China, causing a significant impact on the local atmospheric environment. The Sudan haboob or American haboob often appears in the wet season, followed by thunderstorm events. In contrast, the LSS in China appears most frequently in relatively dry season. The lack of observational data in weather conditions before their formation, during their development and after their disappearance have hindered our understanding of the evolution mechanism of LSS/haboobs. This paper provides a review of the current status and model studies on LSS/haboobs in different time and space to characterize the weather conditions and triggering mechanisms for LSS/haboobs occurrence, as well as highlight the subject for further understanding of LSS/haboobs. LSS are always followed by the occurrence of a dry squall. The interaction of dust radiation heating in the near-surface mixing layer with a mesoscale anticyclone air mass (cold-air pool) in the upper layer is the key process that leads to an LSS. Haboobs are followed by the occurrence of a wet squall. The release of latent heat due to the condensation of water vapor, involving moist convection and cold downdraughts, is the main driving force that cause the occurrence of a haboob. For a better understanding of the characteristics of the wind-sand two-phase flow and the mechanism of energy dissipation in LSS/haboobs, further accumulation of meteorological observation data and small-scale multiple-phase numerical simulations are required.

Severe dust outbreaks and high dust loading over Eastern Africa and the Red Sea are frequently detected in the summer season. Observations suggest that small-scale dynamic and orographic effects, from both the Arabian and African sides, strongly contribute to dust plume formation. To better understand these processes, we present here the first high-resolution modeling study of a dust outbreak in June 2012 developed over East Africa, the Red Sea, and the Arabian Peninsula. Using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) component, we identified several dust generating dynamical processes that range from convective to synoptic scales, including synoptic cyclones, nocturnal low-level jets, and cold pools of mesoscale convective systems. The simulations reveal an eastward transport of African dust across the Red Sea. Over the northern part of the Red Sea, most of the dust transport occurs above 2 km height, whereas across the central and southern parts of the sea; dust is mostly transported below 2 km height. Dust is the dominant contributor (87%) to the aerosol optical depth, producing a domain average cooling effect of −12.1 W m−2 at the surface, a warming of 7.1 W m−2 in the atmosphere, and a residual cooling of −4.9 W m−2 at the top of the atmosphere. Both dry and wet deposition processes contribute significantly to dust removal from the atmosphere. Model results compare well with available ground-based and satellite observations but generally underestimate the observed maximum values of aerosol optical depth. The satellite-retrieved mean optical depth at some locations is underestimated by a factor of 2. A sensitive experiment suggests that these large local differences may result from poor characterization of dust emissions in some areas of the modeled domain. In this case study we successfully simulate the major fine-scale dust generating dynamical processes, explicitly resolving convection and haboob formation. The future development of this novel approach will be beneficial for dust research, assuming steady growth of available computational power.

Recent eld campaigns have shown that haboob dust storms, formed by convective cold pool outflows, contribute a significant fraction of dust uplift over the Sahara and Sahel in summer. However, in-situ observations are sparse and haboobs are frequently concealed by clouds in satellite imagery. Furthermore, most large-scale weather and climate models lack haboobs, because they do not explicitly represent convection. Here a one-year long model run with explicit representation of convection delivers the first full seasonal cycle of haboobs over northern Africa. Using conservative estimates, the model suggests that haboobs contribute one fifth of the annual dust-generating winds over northern Africa, one fourth between May and October, and one third over the western Sahel during this season. A simple parameterization of haboobs has recently been developed for models with parameterized convection, based on the downdraft mass flux of convection schemes. It is applied here to two model runs with different horizontal resolutions, and assessed against the explicit run. The parameterization succeeds in capturing the geographical distribution of haboobs and their seasonal cycle over the Sahara and Sahel. It can be tuned to the different horizontal resolutions, and different formulations are discussed with respect to the frequency of extreme events. The results show that the parameterization is reliable and may solve a major and long-standing issue in simulating dust storms in large-scale weather and climate models.

Cold pool outflows, generated by downdrafts from moist convection, can generate strong winds and therefore uplift of mineral dust. These so-called haboob convective dust storms occur over all major dust source areas worldwide and contribute substantially to emissions in northern Africa, the world’s largest source. Most large-scale models lack convective dust storms because they do not resolve moist convection, relying instead on convection schemes. The authors suggest a parameterization of convective dust storms to account for their contribution in such large-scale models. The parameterization is based on a simple conceptual model, in which the downdraft mass flux from the convection scheme spreads out radially in a cylindrical cold pool. The parameterization is tested with a set of Met Office Unified Model runs for June and July 2006 over West Africa. It is calibrated with a convection-permitting run and applied to a convection-parameterized run. The parameterization successfully produces the extensive area of dust-generating winds from cold pool outflows over the southern Sahara. However, this area extends farther to the east and dust-generating winds occur earlier in the day than in the convection-permitting run. These biases are caused by biases in the convection scheme. It is found that the location and timing of dust-generating winds are weakly sensitive to the parameters of the conceptual model. The results demonstrate that a simple parameterization has the potential to correct a major and long-standing limitation in global dust models.

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.

The dust cycle plays an important role in the atmospheric processes. The levels of dust concentration in the Arabian cities are quite high, a fact that affects air quality. A better understanding of this phenomenon may lead in reduced impacts. Towards this direction, an integrated modeling approach has been selected and applied in SW Saudi Arabia. More specifically, we discuss the characteristics of the dust production processes using the RAMS/ICLAMS multiscale model. A series of very high resolution simulations have been performed and potential mitigation actions are discussed. A reduction in dust concentration is evident by changing the landscape characteristics. Extreme dust events affect the study areas despite the tested activities and changes. A characteristic example is the “haboobs”.

Hundreds to thousands of tons of mineral dust are emitted from the eartha s deserts to the atmosphere each year. Subsequently, mineral dust can be transported over thousands of kilometres with the prevailing winds in the atmosphere until it is deposited on land or in the ocean. On the one hand, the atmospheric dust transport and deposition has an important impact on human health and the eartha s climate system. On the other hand, the dust emission, transport and deposition is controlled by parameters of climate change such as precipitation, wind speed, temperature and vegetation cover. Last but not least, the sensitivity of mineral dust properties to environmental parameters is used as a proxy to reconstruct the climate of the past which is required to test climate models. The large mineral dust emissions, ita s relation to climate and impact on human health underscores the importance to understand the dust cycle. However, research gaps still exist with respect to modern emission, transport and deposition of mineral dust. The Saharan desert is the worlda s largest source of atmospheric mineral dust and has been studied at least since the 18th century. Up to now, the major potential dust source areas are known and it has been unravelled that precipitation results in a decrease in the particle size of deposited Saharan dust on the NW African margin. Further, it is well-known that the seasonal change in insolation on the African continent results in a seasonal change in the altitude of Saharan dust transport. However, research gaps still exists with respect to the influence of the seasonal change in the dust transport on the resulting particle size, mineralogical composition and provenance of Saharan dust. Therefore, the aim of the present Ph.D. thesis was to investigate whether the seasonal change in atmospheric circulation results in a seasonal variation in particle size, mineralogical composition and provenance of Saharan dust. The strategy was to measure the particle size and mineralogy of modern Saharan dust collected during several years onshore NW Africa in continental dust traps and offshore NW Africa in marine sediment trap moorings. By comparing the particle size and mineralogy data to concurrent meteorological data and satellite images, possible connections between the dust properties and meteorological conditions were inferred. Dust which deposited offshore NW Africa was transported with the trades in winter and in the Saharan air layer (SAL) during summer. The particle size of the deposited dust varied seasonally according to dust-storm events year-round, trade-wind speed in winter and wet deposition from the SAL in summer. A seasonal change in the dust mineralogical composition and provenance was observed which could be related to the seasonal change in the dust transport. Onshore NW Africa, the particle size of deposited dust varied seasonally according to meteorological parameters depending on the location of the sampling site. In the major dust source area at 20 AdegreeN, dust was predominantly transported in the trade wind layer year-round. Therefore, the particle size varied seasonally according to the trade wind speed and the mineralogical composition and dust sources according to the direction of the trade winds. In contrast, the particle size of Saharan dust deposited outside a major dust source area at 15 AdegreeN was controlled by the dust transport distance during spring and by the wet deposition from the SAL during summer.

Mineral dust is the most important natural aerosol type by mass, with northern Africa the most prominent source region worldwide. Dust particles are lifted into the atmosphere by strong winds over arid or semiarid soils through a range of emission mechanisms, the most important of which is saltation. Dust particles are mixed vertically by turbulent eddies in the desert boundary layer (up to 6km) or even higher by convective and frontal circulations. The meteorological systems that generate winds strong enough for dust mobilization cover scales from dust devils (~100m) to large dust outbreaks related to low- and high-pressure systems over subtropical northern Africa (thousands of kilometers) and include prominent atmospheric features such as the morning breakdown of low-level jets forming in the stable nighttime boundary layer and cold pools emanating from deep convective systems (so-called haboobs). Dust particles are transported in considerable amounts from northern Africa to remote regions such as the Americas and Europe. The removal of dust particles from the atmosphere occurs through gravitational settling, molecular and turbulent diffusion (dry deposition), as well as in-cloud and sub-cloud scavenging (wet deposition). Advances in satellite technology and numerical dust models (including operational weather prediction systems) have led to considerable progress in quantifying the temporal and spatial variability of dust from Africa, but large uncertainties remain for practically all stages of the dust cycle. The annual cycle of dustiness is dominated by the seasonal shift of rains associated with the West African monsoon and the Mediterranean storm track. In summer, maximum dust loadings are observed over Mauritania and Mali, and the main export is directed toward the Caribbean Sea, creating the so-called elevated Saharan Air Layer. In winter the northeasterly harmattan winds transport dust to the tropical Atlantic and across to southern America, usually in a shallower layer. Mineral dust has a multitude of impacts on climate and weather systems but also on humans (air pollution, visibility, erosion). Nutrients contained in dust fertilize marine and terrestrial ecosystems and therefore impact the global carbon cycle. Dust affects the energy budget directly through interactions with short- and long-wave radiation, with details depending crucially on particle size, shape, and chemical composition. Mineral dust particles are the most important ice-nuclei worldwide and can also serve as condensation nuclei in liquid clouds, but details are not well understood. The resulting modifications to cloud characteristics and precipitation can again affect the energy (and water) budget. Complicated responses and feedbacks on atmospheric dynamics are known, including impacts on regional-scale circulations, sea-surface temperatures, surface fluxes and boundary layer mixing, vertical stability, near-surface winds, soil moisture, and vegetation (and therefore again dust emission). A prominent example of such complex interactions is the anti-correlation between African dust and Atlantic hurricane activity from weekly to decadal timescales, the causes of which remain difficult to disentangle. Particularly in the early 21st century, research on African dust intensified substantially and became more interdisciplinary, leading to some significant advances in our understanding of this fascinating and multifaceted element of the Earth system.

A dust storm of fearful proportions hit Phoenix in the early evening hours of 5 July 2011. This storm, an American haboob, was predicted hours in advance because numerical, land–atmosphere modeling, computing power and remote sensing of dust events have improved greatly over the past decade. High-resolution numerical models are required for accurate simulation of the small scales of the haboob process, with high velocity surface winds produced by strong convection and severe downbursts. Dust productive areas in this region consist mainly of agricultural fields, with soil surfaces disturbed by plowing and tracks of land in the high Sonoran Desert laid barren by ongoing draught. Model simulation of the 5 July 2011 dust storm uses the coupled atmospheric-dust model NMME–DREAM (Non-hydrostatic Mesoscale Model on E grid, Janjic et al., 2001; Dust REgional Atmospheric Model, Nickovic et al., 2001; Pérez et al., 2006) with 4 km horizontal resolution. A mask of the potentially dust productive regions is obtained from the land cover and the normalized difference vegetation index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The scope of this paper is validation of the dust model performance, and not use of the model as a tool to investigate mechanisms related to the storm. Results demonstrate the potential technical capacity and availability of the relevant data to build an operational system for dust storm forecasting as a part of a warning system. Model results are compared with radar and other satellite-based images and surface meteorological and PM10 observations. The atmospheric model successfully hindcasted the position of the front in space and time, with about 1 h late arrival in Phoenix. The dust model predicted the rapid uptake of dust and high values of dust concentration in the ensuing storm. South of Phoenix, over the closest source regions (~25 km), the model PM10 surface dust concentration reached ~2500 μg m−3, but underestimated the values measured by the PM10 stations within the city. Model results are also validated by the MODIS aerosol optical depth (AOD), employing deep blue (DB) algorithms for aerosol loadings. Model validation included Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), equipped with the lidar instrument, to disclose the vertical structure of dust aerosols as well as aerosol subtypes. Promising results encourage further research and application of high-resolution modeling and satellite-based remote sensing to warn of approaching severe dust events and reduce risks for safety and health.

A slow-moving complex of thunderstorms formed across northwestern Nevada on 10 June 2013 in the deformation zone of an approaching upper-level low-pressure system. Storm redevelopment along outflow boundaries resulted in urban and rural flash flooding. On the eastern flank of the thunderstorm complex, strong outflow boundaries lofted dust to form a large haboob. The haboob propagated eastward across northcentral Nevada and resulted in a 27-car pileup on Interstate 80 near Winnemucca. Three examples are presented that demonstrate how dual-polarization radar technology aided forecasters in (i) discriminating heavy rain from hail and (ii) tracking the haboob.