Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements

Rosenberg, Phil; Parker, Douglas J.; Ryder, Claire L.; Marsham, John H.; Garcia-Carreras, Luis; Dorsey, J. R.; Brooks, Ian M.; Dean, A.; Crosier, Jonathan; McQuaid, James B.; Washington, Richard

doi:10.1002/2013jd021255

Cited by 45 publications

(64 citation statements)

References 64 publications

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“…For this ratio to be consistent with the ~3.4% estimate of global DDP flux, the dust flux per DDP needs to be 700 to 1400 times the dust flux per area caused by resolved winds. This is large, but may be conceivable, given the (i) uncertainty in this value from the uncertainty in σ discussed below and (ii) that dust devil cores have updrafts collocated with intense emission and thus provide good conditions to lift large particles, which affect mass fluxes considerably [ Rosenberg et al ., ].…”

Section: Resultsmentioning

confidence: 99%

Quantifying global dust devil occurrence from meteorological analyses

Jemmett-Smith

Marsham

Knippertz

et al. 2015

Geophysical Research Letters

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Dust devils and nonrotating dusty plumes are effective uplift mechanisms for fine particles, but their contribution to the global dust budget is uncertain. By applying known bulk thermodynamic criteria to European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses, we provide the first global hourly climatology of potential dust devil and dusty plume (PDDP) occurrence. In agreement with observations, activity is highest from late morning into the afternoon. Combining PDDP frequencies with dust source maps and typical emission values gives the best estimate of global contributions of 3.4% (uncertainty 0.9–31%), 1 order of magnitude lower than the only estimate previously published. Total global hours of dust uplift by dry convection are ∼0.002% of the dust-lifting winds resolved by ECMWF, consistent with dry convection making a small contribution to global uplift. Reducing uncertainty requires better knowledge of factors controlling PDDP occurrence, source regions, and dust fluxes induced by dry convection. Key Points Global potential dust devil occurrence quantified from meteorological analyses Climatology shows realistic diurnal cycle and geographical distribution Best estimate of global contribution of 3.4% is 10 times smaller than the previous estimate

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Section: Resultsmentioning

confidence: 99%

Quantifying global dust devil occurrence from meteorological analyses

Jemmett-Smith

Marsham

Knippertz

et al. 2015

Geophysical Research Letters

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“…Dots show the in situ measured dust particle size distribution at emission. Shown are measurements from Gill72 (Gillette et al, 1972), Gill74a (Gillette, 1974), Gill74b , Sow2009 (Sow et al, 2009), Shao2011 (Shao et al, 2011), Frat2 (Fratini et al, 2007), and Ros14 (Rosenberg et al, 2014 downwind these source areas and, thus, is further investigated using the AERONET data in the following section.…”

Section: Spatial Distribution Of Aodmentioning

confidence: 99%

Effects of Particle Nonsphericity on Dust Optical Properties in a Forecast System: Implications for Model‐Observation Comparison

et al. 2019

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Mineral dust is a key player in the Earth system that affects the weather and climate through absorbing and scattering the radiation. Such effects strongly depend on the optical properties of the particles that are in turn affected by the particle shape. For simplicity, dust particles are usually assumed to be spherical. But this assumption can lead to large errors in modeling and remote sensing applications. This study investigates the impact of dust particle shape on its direct radiative effect in a next‐generation atmospheric modeling system ICON‐ART (ICOsahedral Nonhydrostatic weather and climate model with Aerosols and Reactive Trace gases) to verify if accounting for nonsphericity enhances the model‐observation agreement. Two sets of numerical experiments are conducted by changing the optical shape of the particles: one assuming spherical particles and the other one assuming a mixture of 35 randomly oriented triaxial ellipsoids. The simulations are compared to MISR (Multiangle Imaging Spectroradiometer), AERONET (Aerosol Robotic Network), and CALIPSO (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation) observations (with focus on North Africa). The results show that consideration of particle nonsphericity increases the dust AOD (Aerosol Optical Depth) at 550 nm by up to 28% and leads to slight enhancement of the agreement between modeled and measured AOD. However, the model performance varies significantly when focusing on specific regions in North Africa. These differences stem from the uncertainties associated with particle size distribution and emission mechanisms in the model configuration. Regarding the attenuated backscatter, the simulated profile assuming nonsphericity differs by a factor of 2 to 5 from the experiment assuming spherical dust and is in a better agreement with the CALIPSO observations.

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“…Hobby et al, 2013;Marsham et al, 2013;Todd et al, 2013) and from aircraft (e.g. Rosenberg et al, 2014;Ryder et al, 2015; 2013). As one of the few measurement campaigns which has reached into the central Sahara, the combined set of Fennec data is unparalleled in its capacity to provide evidence as to the nature of dust activity over the central desert.…”

Section: Introductionmentioning

confidence: 99%

The influence of dust optical properties on the colour of simulated MSG-SEVIRI Desert Dust infrared imagery

et al. 2018

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Abstract. Satellite imagery of atmospheric mineral dust is sensitive to the optical properties of the dust, governed by the mineral refractive indices, particle size, and particle shape. In infrared channels the imagery is also sensitive to the dust layer height and to the surface and atmospheric environment. Simulations of mineral dust in infrared "Desert Dust" imagery from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) have been performed, using the COSMO-MUSCAT (COSMO: COnsortium for Smallscale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model) dust transport model and the Radiative Transfer for TOVS (RTTOV) program, in order to investigate the sensitivity of the imagery to assumed dust properties. This paper introduces the technique and performs initial validation and comparisons with SEVIRI measurements over North Africa for daytime hours during 6 months covering June and July of 2011-2013. Using T-matrix scattering theory and assuming the dust particles to be spherical or spheroidal, wavelength-and size-dependent dust extinction values are calculated for a number of different dust refractive index databases, along with several values of the particle aspect ratio, denoting the particle shape. The consequences for the infrared extinction values of both the particle shape and the particle orientation are explored: this analysis shows that as the particle asphericity increases, the extinctions increase if the particles are aligned horizontally, and decrease if they are aligned vertically. Randomly oriented spheroidal particles have very similar infrared extinction properties as spherical particles, whereas the horizontally and vertically aligned particles can be considered to be the upper and lower bounds on the extinction values. Inputting these values into COSMO-MUSCAT-RTTOV, it is found that spherical particles do not appear to be sufficient to describe fully the resultant colour of the dust in the infrared imagery. Comparisons of SEVIRI and simulation colours indicate that of the dust types tested, the dust refractive index dataset produced by Volz (1973) shows the most similarity in the colour response to dust in the SEVIRI imagery, although the simulations have a smaller range of colour than do the observations. It is also found that the thermal imagery is most sensitive to intermediately sized particles (radii between 0.9 and 2.6 µm): larger particles are present in too small a concentration in the simulations, as well as with insufficient contrast in extinction between wavelength channels, to have much ability to perturb the resultant colour in the SEVIRI dust imagery.

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Quantifying particle size and turbulent scale dependence of dust flux in the Sahara using aircraft measurements

Cited by 45 publications

References 64 publications

Quantifying global dust devil occurrence from meteorological analyses

Quantifying global dust devil occurrence from meteorological analyses

Effects of Particle Nonsphericity on Dust Optical Properties in a Forecast System: Implications for Model‐Observation Comparison

The influence of dust optical properties on the colour of simulated MSG-SEVIRI Desert Dust infrared imagery

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