The electrification of dust-lofting gust fronts (‘haboobs’) in the Sahel

Williams, Earle; Nathou, N.; Hicks, E.; Pontikis, Constantin; Russell, Bruce A.; Miller, Mark A.; Bartholomew, Mary Jane

doi:10.1016/j.atmosres.2008.05.017

Cited by 103 publications

(87 citation statements)

References 21 publications

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“…These short-lived convective systems and their related cold pools could be responsible for the dust mobilisation seen in the lidar data in the vicinity of Niamey. For instance, Williams et al (2008) have shown that virtually every cold outflow from moist convection in the vicinity of Niamey was a source of substantial dust uplift throughout the wet season. Lidar measurements evidence that the reduction of the dust load over Benin and southern Niger occurred consistently north of 8 • N (this is corroborated at the local scale by AERONET and MODIS AODs), which suggests that this decrease is mostly related to the variability of the dust load upstream.…”

Section: The Vertical Distribution Of Dust Over Southern Niger and Bementioning

confidence: 99%

Multi‐platform observations of a springtime case of Bodélé and Sudan dust emission, transport and scavenging over West Africa

Flamant¹,

Lavaysse²,

Todd³

et al. 2009

Quart J Royal Meteoro Soc

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ABSTRACT:The structure of the Saharan air layer over Niger and Benin during a major springtime dust event from the Bodélé region and Sudan is investigated using airborne lidar and dropsonde measurements. Aircraft operations were conducted on 13 and 14 June 2006, within the framework of the African Monsoon Multidisciplinary Analysis Special Observing Period. Complementary ground-based and satellite observations, as well as European Centre for Medium-range Weather Forecasts analyses are used to investigate the regional aspects of emission, transport and deposition in the period from 9 to 14 June 2006, to provide a framework for the interpretation of the airborne measurements. The study details the transport patterns of dust from eastern Saharan sources towards the southwest in the springtime, and highlights the role of the intertropical discontinuity and the Darfur mountains in injecting the aerosols from Bodélé and Sudan, respectively, over the monsoon flow, and in the African easterly jet (AEJ) region. It also illustrates the impact of the daily variability of the emissions in the source regions on the dust load advected westward by the AEJ and observed over Benin. The impact of a mesoscale convective system (MCS) on the dust load and vertical distribution observed over Benin and southern Niger was also investigated, nearly 12 hours after its passage over Benin. The only discernible impact on the dust distribution is observed to be associated with widespread subsidence in the wake of the MCS, over northern Benin and Niger. Wet scavenging related to convective or stratiform rain could not be observed, as processed air masses were replaced by fresh dust transported in the upper Saharan air layer by the AEJ. Over southern Benin, the dust distribution appeared to be mostly controlled by processes affecting the planetary boundary layer upstream, i.e. over Nigeria or Chad. Because springtime dust from remote eastern sources (such as observed in this case) is mainly transported into the AEJ, it could impact on the radiation budget in the AEJ region, thereby possibly modifying the West African weather at the synoptic scale. Copyright

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Section: The Vertical Distribution Of Dust Over Southern Niger and Bementioning

confidence: 99%

Multi‐platform observations of a springtime case of Bodélé and Sudan dust emission, transport and scavenging over West Africa

Flamant¹,

Lavaysse²,

Todd³

et al. 2009

Quart J Royal Meteoro Soc

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“…Z DR was as low as -5 dB in regions with horizontal reflectivity factor (Z H ) near 10 dBZ. For this dust storm, which was observed to reach an altitude of nearly 3 km, negative Z DR values were attributed to debris elements such as sticks and grass that were oriented vertically in a strong electric field (Zhang et al 2015)-as has been measured in a Sahelian dust event (Williams et al 2009). It was hypothesized that such strongly negative values of Z DR may be operationally useful for dust storm monitoring.…”

Section: Introductionmentioning

confidence: 99%

“…Non-meteorological applications of polarimetric radar observations have included military chaff (Zrnić and Ryzhkov 2004), sea clutter (e.g., Alku et al 2015), smoke plumes (Melnikov et al 2009), and biological scatterers (e.g., Van Den Broeke 2013). While radar observations of dust storms have been presented in the literature (e.g., Williams et al 2009), polarimetric dust storm observations have been relatively sparse. S-band polarimetric dust storm observations have been presented from an Arizona event in which large, consistent regions of strongly negative Z DR were noted (Zhang et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Polarimetric radar observations of dust storms at C- and S-band

Broeke

Alsarraf²

2016

J. Operational Meteor.

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“…Among the sonde flights, six of them were carrying integrated packages of water vapour, ozone and particle measuring instruments. They were flown as close as possible to MCSs identified on Meteosat Second Generation (MSG) and MIT C-band radar images (Williams et al, 2009). The instruments flown on each were a FLASH-B Lyman-alpha hygrometer (Yushkov et al, 1998), a backscatter sonde (Rosen and Kjome, 1991), an Electro-Chemical Cell (ECC) ozonesonde and a Vaisala RS-92 meteorological package (pressure, temperature, humidity and GPS 3-D location).…”

Section: Introductionmentioning

confidence: 99%

Hydration of the lower stratosphere by ice crystal geysers over land convective systems

et al. 2009

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Abstract. The possible impact of deep convective overshooting over land has been explored by six simultaneous soundings of water vapour, particles and ozone in the lower stratosphere next to Mesoscale Convective Systems (MCSs) during the monsoon season over West Africa in Niamey, Niger in August 2006. The water vapour measurements were carried out using a fast response FLASH-B Lyman-alpha hygrometer. The high vertical resolution observations of the instrument show the presence of accumulation of enhanced water vapour layers between the tropopause at 370 K and the 420 K level. Most of these moist layers are shown connected with overshooting events occurring upwind as identified from satellite IR images over which the air mass probed by the sondes passed during the three previous days. In the case of a local overshoot identified by echo top turrets above the tropopause by the MIT C-band radar also in Niamey, tight coincidence was found between enhanced water vapour, ice crystal and ozone dip layers indicative of fast uplift of tropospheric air across the tropopause. The water vapour mixing ratio in the enriched layers exceeds frequently by 1-3 ppmv the average 6 ppmv saturation ratio at the tropopause and by up to 7 ppmv in the extreme case of local storm in coincidence with the presence of ice crystals. The presence of such layers strongly suggests hydration of the lower stratosphere by geyser-like injection of ice particles over overshooting turrets. The pile-like increase of water vapour up to 19 km seen by the high-resolution hygrometer during the season of maximum temperature of the tropopause, suggests that the above Correspondence to: S. Khaykin (sehamic@yandex.ru) hydration mechanism may contribute to the summer maximum moisture in the lower stratosphere. If this interpretation is correct, hydration by ice geysers across the tropopause might be an important contributor to the stratospheric water vapour budget.

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The electrification of dust-lofting gust fronts (‘haboobs’) in the Sahel

Cited by 103 publications

References 21 publications

Multi‐platform observations of a springtime case of Bodélé and Sudan dust emission, transport and scavenging over West Africa

Multi‐platform observations of a springtime case of Bodélé and Sudan dust emission, transport and scavenging over West Africa

Polarimetric radar observations of dust storms at C- and S-band

Hydration of the lower stratosphere by ice crystal geysers over land convective systems

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