Dust Emission Model Research Articles

ERRATUM: “THE HERSCHEL INVENTORY OF THE AGENTS OF GALAXY EVOLUTION (HERITAGE) IN THE MAGELLANIC CLOUDS, A HERSCHEL OPEN TIME KEY PROGRAM” (2013, AJ, 146, 62)

We provide a corrected Table 4 that lists the total galaxy fluxes for the HERTIAGE bands and corresponding Figure 19 which plots these fluxes in comparison to prior measurements These corrected fluxes differ by up to 41% to what we reported in the original paper. These revised fluxes utilize a more appropriate subtraction of the Milky Way Foreground Cirrus emission which contaminates especially the PACS 100 and 160 micron bands. The subtraction process uses the HI 21 cm emission to develop a model for the MW cirrus dust emission. In addition, the better subtraction process corrected for an over subtraction of the background in the SPIRE images of the SMC that occurred during the original data processing. The need for these better foreground subtractions was realized while working on an analysis of the dust masses and gas-to-dust ratios in the LMC and SMC reported by Gordon et al. (2014) and Roman-Duval et al. (2014). After the subtraction has been done, the fluxes were derived by simply summing up all the pixels in the image. The errors we quote for the fluxes reflect the absolute flux calibration errors for extended sources which are approx.10% for PACS and approx. 8% for SPIRE. In the revised Figure 19, we confirm that these corrected global fluxes remain within the range of prior global measurements for both the LMC and SMC. Indeed, the shape of the corrected spectral energy distributions appears better aligned with prior measurements.

Study of morphology and stellar content of the Galactic H ii region IRAS 16148−5011

An investigation of the IRAS 16148−5011 region – a cluster at a distance of 3.6 kpc – is presented here, carried out using multiwavelength data in near-infrared (NIR) from the 1.4 m Infrared Survey Facility telescope, mid-infrared (MIR) from the archival Spitzer GLIMPSE (Galactic Legacy Infrared Midplane Survey Extraordinaire) survey, far-infrared (FIR) from the Herschel archive, and low-frequency radio continuum observations at 1280 and 843 MHz from the Giant Metrewave Radio Telescope and Molonglo Survey archive, respectively. A combination of NIR and MIR data is used to identify 7 Class I and 133 Class II sources in the region. Spectral energy distribution (SED) analysis of selected sources reveals a 9.6 M⊙ high-mass source embedded in nebulosity. However, Lyman continuum luminosity calculation using radio emission – which shows a compact H ii region – indicates the spectral type of the ionizing source to be earlier than B0-O9.5. Free–free emission SED modelling yields the electron density as 138 cm−3, and thus the mass of the ionized hydrogen as ∼16.4 M⊙. Thermal dust emission modelling, using the FIR data from Herschel and performing modified blackbody fits, helped us construct the temperature and column density maps of the region, which show peak values of 30 K and 3.3 × 1022 cm−2, respectively. The column density maps reveal an AV > 20 mag extinction associated with the nebular emission, and weak filamentary structures connecting dense clumps. The clump associated with this IRAS object is found to have dimensions of ∼ 1.1 pc × 0.8 pc, and a mass of 1023 M⊙.

MODELING THERMAL DUST EMISSION WITH TWO COMPONENTS: APPLICATION TO THEPLANCKHIGH FREQUENCY INSTRUMENT MAPS

We apply the Finkbeiner et al. (1999) two-component thermal dust emission model to the Planck HFI maps. This parametrization of the far-infrared dust spectrum as the sum of two modified blackbodies serves as an important alternative to the commonly adopted single modified blackbody (MBB) dust emission model. Analyzing the joint Planck/DIRBE dust spectrum, we show that two-component models provide a better fit to the 100-3000 GHz emission than do single-MBB models, though by a lesser margin than found by Finkbeiner et al. (1999) based on FIRAS and DIRBE. We also derive full-sky 6.1' resolution maps of dust optical depth and temperature by fitting the two-component model to Planck 217-857 GHz along with DIRBE/IRAS 100 micron data. Because our two-component model matches the dust spectrum near its peak, accounts for the spectrum's flattening at millimeter wavelengths, and specifies dust temperature at 6.1' FWHM, our model provides reliable, high-resolution thermal dust emission foreground predictions from 100 to 3000 GHz. We find that, in diffuse sky regions, our two-component 100-217 GHz predictions are on average accurate to within 2.2%, while extrapolating the Planck Collaboration (2013a) single-MBB model systematically underpredicts emission by 18.8% at 100 GHz, 12.6% at 143 GHz and 7.9% at 217 GHz. We calibrate our two-component optical depth to reddening, and compare with reddening estimates based on stellar spectra. We find the dominant systematic problems in our temperature/reddening maps to be zodiacal light on large angular scales and the cosmic infrared background anisotropy on small angular scales.

An improved dust emission model – Part 2: Evaluation in the Community Earth System Model, with implications for the use of dust source functions

Abstract. The complex nature of mineral dust aerosol emission makes it a difficult process to represent accurately in weather and climate models. Indeed, results in the companion paper indicate that many large-scale models underestimate the dust flux's sensitivity to the soil's threshold friction velocity for erosion. We hypothesize that this finding explains why many dust cycle simulations are improved by using an empirical dust source function that shifts emissions towards the world's most erodible regions. Here, we both test this hypothesis and evaluate the performance of the new dust emission parameterization presented in the companion paper. We do so by implementing the new emission scheme into the Community Earth System Model (CESM) and comparing the resulting dust cycle simulations against an array of measurements. We find that the new scheme shifts emissions towards the world's most erodible regions in a manner that is strikingly similar to the effect of implementing a widely used source function based on satellite observations of dust source regions. Furthermore, model comparisons against aerosol optical depth measurements show that the new physically based scheme produces a statistically significant improvement in CESM's representation of dust emission, which exceeds the improvement produced by implementing a source function. These results indicate that the need to use an empirical source function is eliminated, at least in CESM, by the additional physics in the new scheme, and in particular by its increased sensitivity to the soil's threshold friction velocity. Since the threshold friction velocity is affected by climate changes, our results further suggest that many large-scale models underestimate the global dust cycle's climate sensitivity.

An improved dust emission model – Part 1: Model description and comparison against measurements

Abstract. Simulations of the dust cycle and its interactions with the changing Earth system are hindered by the empirical nature of dust emission parameterizations in weather and climate models. Here we take a step towards improving dust cycle simulations by using a combination of theory and numerical simulations to derive a physically based dust emission parameterization. Our parameterization is straightforward to implement into large-scale models, as it depends only on the wind friction velocity and the soil's threshold friction velocity. Moreover, it accounts for two processes missing from most existing parameterizations: a soil's increased ability to produce dust under saltation bombardment as it becomes more erodible, and the increased scaling of the dust flux with wind speed as a soil becomes less erodible. Our treatment of both these processes is supported by a compilation of quality-controlled vertical dust flux measurements. Furthermore, our scheme reproduces this measurement compilation with substantially less error than the existing dust flux parameterizations we were able to compare against. A critical insight from both our theory and the measurement compilation is that dust fluxes are substantially more sensitive to the soil's threshold friction velocity than most current schemes account for.

DUST AND GAS IN THE MAGELLANIC CLOUDS FROM THE HERITAGEHERSCHELKEY PROJECT. I. DUST PROPERTIES AND INSIGHTS INTO THE ORIGIN OF THE SUBMILLIMETER EXCESS EMISSION

The dust properties in the Large and Small Magellanic Clouds are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 micron. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a power- law emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models we investigate the origin of the submm excess; defined as the submillimeter (submm) emission above that expected from SMBB models fit to observations < 200 micron. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 micron submm excesses of 27% and 43% for the LMC and SMC, respectively. Adopting gas masses from previous works, the gas-to-dust ratios calculated from our the fitting results shows that the TTMBB fits require significantly more dust than are available even if all the metals present in the interstellar medium (ISM) were condensed into dust. This indicates that the submm excess is more likely to be due to emissivity variations than a second population of colder dust. We derive integrated dust masses of (7.3 +/- 1.7) x 10^5 and (8.3 +/- 2.1) times 10^4 M(sun) for the LMC and SMC, respectively. We find significant correlations between the submm excess and other dust properties; further work is needed to determine the relative contributions of fitting noise and ISM physics to the correlations.

Modeling and predicting the shape of the far-infrared to submillimeter emission in ultra-compact HII regions and cold clumps

Dust properties are very likely affected by the environment in which dust grains evolve. For instance, some analyses of cold clumps (7 K- 17 K) indicate that the aggregation process is favored in dense environments. However, studying warm (30 K-40 K) dust emission at long wavelength ($\lambda$$>$300 $\mu$m) has been limited because it is difficult to combine far infared-to-millimeter (FIR-to-mm) spectral coverage and high angular resolution for observations of warm dust grains. Using Herschel data from 70 to 500 $\mu$m, which are part of the Herschel infrared Galactic (Hi-GAL) survey combined with 1.1 mm data from the Bolocam Galactic Plane Survey (BGPS), we compared emission in two types of environments: ultra-compact HII (UCHII) regions, and cold molecular clumps (denoted as cold clumps). With this comparison we tested dust emission models in the FIR-to-mm domain that reproduce emission in the diffuse medium, in these two environments (UCHII regions and cold clumps). We also investigated their ability to predict the dust emission in our Galaxy. We determined the emission spectra in twelve UCHII regions and twelve cold clumps, and derived the dust temperature (T) using the recent two-level system (TLS) model with three sets of parameters and the so-called T-$\beta$ (temperature-dust emissvity index) phenomenological models, with $\beta$ set to 1.5, 2 and 2.5. We tested the applicability of the TLS model in warm regions for the first time. This analysis indicates distinct trends in the dust emission between cold and warm environments that are visible through changes in the dust emissivity index. However, with the use of standard parameters, the TLS model is able to reproduce the spectral behavior observed in cold and warm regions, from the change of the dust temperature alone, whereas a T-$\beta$ model requires $\beta$ to be known.

Comparison of the predictions of two road dust emission models with the measurements of a mobile van

Abstract. The predictions of two road dust suspension emission models were compared with the on-site mobile measurements of suspension emission factors. Such a quantitative comparison has not previously been reported in the reviewed literature. The models used were the Nordic collaboration model NORTRIP (NOn-exhaust Road TRaffic Induced Particle emissions) and the Swedish–Finnish FORE model (Forecasting Of Road dust Emissions). These models describe particulate matter generated by the wear of road surface due to traction control methods and processes that control the suspension of road dust particles into the air. An experimental measurement campaign was conducted using a mobile laboratory called SNIFFER, along two selected road segments in central Helsinki in 2007 and 2008. The suspended PM10 concentration was measured behind the left rear tyre and the street background PM10 concentration in front of the van. Both models reproduced the measured seasonal variation of suspension emission factors fairly well during both years at both measurement sites. However, both models substantially under-predicted the measured emission values. The article illustrates the challenges in conducting road suspension measurements in densely trafficked urban conditions, and the numerous requirements for input data that are needed for accurately applying road suspension emission models.

Introduction to a Special Issue of Aeolian Research Airborne mineral dust contaminants: Impacts on human health and the environment.

Introduction to a Special Issue of Aeolian Research Airborne mineral dust contaminants: Impacts on human health and the environment.

How important are atmospheric depressions and mobile cyclones for emitting mineral dust aerosol in North Africa?

Abstract. This study presents the first quantitative estimate of the mineral dust emission associated with atmospheric depressions and mobile cyclones in North Africa. Atmospheric depressions are automatically tracked at 925 hPa based on ERA-Interim data from the European Centre for Medium-Range Weather Forecasts for 1989–2008. A set of filter criteria is applied to identify mobile cyclones, i.e. migrating and long-lived cyclones. The shorter term cyclone is used as a synonym for mobile cyclones. Dust emission is calculated with a dust emission model driven by 10 m winds and soil moisture from ERA-Interim. Emission peaks during winter and spring with spatial averages of 250–380 g m−2 per month. Comparison of the dust source activation frequency from the model against SEVIRI satellite observation shows a good agreement in the Bodélé Depression but differences in the north and west of North Africa. Depressions are abundant, particularly in summer when the Saharan heat low is situated over West Africa and during spring in the lee of the Atlas Mountains. Up to 90% (55% annually and spatially averaged) of dust emission occurs within 10 degrees of these depressions, with embedded mechanisms such as nocturnal low-level jets playing a role. Cyclones are rarer and occur primarily north of 20° N in spring in agreement with previous studies and over summertime West Africa consistent with near-surface signatures of African Easterly Waves. Dust emission within 10 degrees of cyclones peaks over Libya with up to 25% in spring. Despite the overall small contribution of 4% annually and spatially averaged, cyclones coincide with particularly intense dust emission events exceeding the climatological mean by a factor of four to eight. Soil moisture weakens dust emission during cyclone passage by about 10%.

Modelling desertification risk in the north-west of Jordan using geospatial and remote sensing techniques

Remote sensing, climate, and ground data were used within a geographic information system (GIS) to map desertification risk in the north-west of Jordan. The approach was based on modelling wind and water erosion and incorporating the results with a map representing the severity of drought. Water erosion was modelled by the universal soil loss equation, while wind erosion was modelled by a dust emission model. The extent of drought was mapped using the evapotranspiration water stress index (EWSI) which incorporated actual and potential evapotranspiration. Output maps were assessed within GIS in terms of spatial patterns and the degree of correlation with soil surficial properties. Results showed that both topography and soil explained 75% of the variation in water erosion, while soil explained 25% of the variation in wind erosion, which was mainly controlled by natural factors of topography and wind. Analysis of the EWSI map showed that drought risk was dominating most of the rainfed areas. The combined effects of soil erosion and drought were reflected on the desertification risk map. The adoption of these geospatial and remote sensing techniques is, therefore, recommended to map desertification risk in Jordan and in similar arid environments.

SPITZEROBSERVATIONS OF DUST EMISSION FROM H II REGIONS IN THE LARGE MAGELLANIC CLOUD

Massive stars can alter physical conditions and properties of their ambient interstellar dust grains via radiative heating and shocks. The HII regions in the Large Magellanic Cloud (LMC) offer ideal sites to study the stellar energy feedback effects on dust because stars can be resolved, and the galaxy's nearly face-on orientation allows us to unambiguously associate HII regions with their ionizing massive stars. The Spitzer Space Telescope survey of the LMC provides multi-wavelength (3.6 to 160 $\mu$m) photometric data of all HII regions. To investigate the evolution of dust properties around massive stars, we have analyzed spatially-resolved IR dust emission from two classical HII regions (N63 and N180) and two simple superbubbles (N70 and N144) in the LMC. We produce photometric spectral energy distributions (SEDs) of numerous small subregions for each region based on its stellar distributions and nebular morphologies. We use DustEM dust emission model fits to characterize the dust properties. Color-color diagrams and model fits are compared with the radiation field (estimated from photometric and spectroscopic surveys). Strong radial variations of SEDs can be seen throughout the regions, reflecting the available radiative heating. Emission from very small grains drastically increases at locations where the radiation field is the highest, while polycyclic aromatic hydrocarbons (PAHs) appear to be destroyed. PAH emission is the strongest in the presence of molecular clouds, provided that the radiation field is low.

THE HEATING OF MID-INFRARED DUST IN THE NEARBY GALAXY M33: A TESTBED FOR TRACING GALAXY EVOLUTION

Because the 8 {\mu}m polycyclic aromatic hydrocarbon (PAH) emission has been found to correlate with other well-known star formation tracers, it has widely been used as a star formation rate (SFR) tracer. There are, however, studies that challenge the accuracy and reliability of the 8 {\mu}m emission as a SFR tracer. Our study, part of the Herschel M33 Extended Survey (HERM33ES) open time key program, aims at addressing this issue by analyzing the infrared emission from the nearby spiral galaxy M33 at the high spatial scale of 75 pc. Combining data from the Herschel Space Observatory and the Spitzer Space Telescope we find that the 8 {\mu}m emission is better correlated with the 250 {\mu}m emission, which traces cold interstellar gas, than with the 24 {\mu}m emission. The L(8)/L(24) ratio is highly depressed in 24 {\mu}m luminous regions, which correlate with known HII regions. We also compare our results with the dust emission models by Draine & Li (2007). We confirm that the depression of 8 {\mu}m PAH emission near star-forming regions is higher than what is predicted by models; this is possibly an effect of increased stellar radiation from young stars destroying the dust grains responsible for the 8 {\mu}m emission as already suggested by other authors. We find that the majority of the 8 {\mu}m emission is fully consistent with heating by the diffuse interstellar medium, similar to what recently determined for the dust emission in M31 by Draine at al. (2013). We also find that the fraction of 8 {\mu}m emission associated with the diffuse interstellar radiation field ranges between 60% and 80% and is 40% larger than the diffuse fraction at 24 {\mu}m.

Numerical validation of a near-field fugitive dust model for vehicles moving on unpaved surfaces

This paper presents a numerical model for evaluating fugitive dust emissions and transport in a near field induced by a moving vehicle. The dust emission model describes the quantity and location of emitted dust. The transport of the dust is recorded by the Lagrangian particle-tracking method, and the turbulence dispersion of particles is modeled stochastically. The presented model is validated numerically for the prediction of dust concentration in a region near the vehicles through a careful comparison with the available experimental data. The simulation results compare reasonably well with the experimental data. This model provides, for the first time, a validated dust emission and transport model suitable for the near field of moving vehicles.

Effect of dead leaves on early spring dust emission in East Asia

Dead leaves remaining after the growing season can suppress dust emission by wind erosion, but this has not been considered in numerical models of dust emission. We investigated the effect of dead leaves by analyzing surface meteorological data and numerical simulations for early spring Asian dust events, and propose a parameterization of the dead-leaf effect. World Meteorological Organization (WMO) synoptic data indicate that high vegetation cover from the previous year can increase the threshold friction velocity for early spring of the following year. The reduction rate of dead leaves is calculated using 10-year averaged monthly vegetation cover data derived from the Normalized Difference Vegetation Index (NDVI), assuming that the amount of dead leaves decreases linearly, and the amount of dead leaves is included in calculating threshold friction velocity. To investigate the effect of dead leaves in simulations of Asian dust events, case studies were carried out with and without the dead-leaf effect for early spring Asian dust events using a Weather Research and Forecasting with Chemistry (WRF-Chem) model with a new dust emission scheme. Including the dead-leaf effect improved the model results, and the modeled surface concentrations are similar to the observed PM10 concentrations.

Estimating aerodynamic roughness over complex surface terrain

AbstractSurface roughness plays a key role in determining aerodynamic roughness length (zo) and shear velocity, both of which are fundamental for determining wind erosion threshold and potential. While zo can be quantified from wind measurements, large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach. Alternative approaches therefore seek to relate zo to morphological roughness metrics. However, dust‐emitting landscapes typically consist of complex small‐scale surface roughness patterns and few metrics exist for these surfaces which can be used to predict zo for modeling wind erosion potential. In this study terrestrial laser scanning was used to characterize the roughness of typical dust‐emitting surfaces (playa and sandar) where element protrusion heights ranged from 1 to 199 mm, over which vertical wind velocity profiles were collected to enable estimation of zo. Our data suggest that, although a reasonable relationship (R2 &gt; 0.79) is apparent between 3‐D roughness density and zo, the spacing of morphological elements is far less powerful in explaining variations in zo than metrics based on surface roughness height (R2 &gt; 0.92). This finding is in juxtaposition to wind erosion models that assume the spacing of larger‐scale isolated roughness elements is most important in determining zo. Rather, our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting zo. This finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments.

Soil organic carbon dust emission: an omitted global source of atmospheric CO2

Soil erosion redistributes soil organic carbon (SOC) within terrestrial ecosystems, to the atmosphere and oceans. Dust export is an essential component of the carbon (C) and carbon dioxide (CO(2)) budget because wind erosion contributes to the C cycle by removing selectively SOC from vast areas and transporting C dust quickly offshore; augmenting the net loss of C from terrestrial systems. However, the contribution of wind erosion to rates of C release and sequestration is poorly understood. Here, we describe how SOC dust emission is omitted from national C accounting, is an underestimated source of CO(2) and may accelerate SOC decomposition. Similarly, long dust residence times in the unshielded atmospheric environment may considerably increase CO(2) emission. We developed a first approximation to SOC enrichment for a well-established dust emission model and quantified SOC dust emission for Australia (5.83 Tg CO(2)-e yr(-1)) and Australian agricultural soils (0.4 Tg CO(2)-e yr(-1)). These amount to underestimates for CO(2) emissions of ≈10% from combined C pools in Australia (year = 2000), ≈5% from Australian Rangelands and ≈3% of Australian Agricultural Soils by Kyoto Accounting. Northern hemisphere countries with greater dust emission than Australia are also likely to have much larger SOC dust emission. Therefore, omission of SOC dust emission likely represents a considerable underestimate from those nations' C accounts. We suggest that the omission of SOC dust emission from C cycling and C accounting is a significant global source of uncertainty. Tracing the fate of wind-eroded SOC in the dust cycle is therefore essential to quantify the release of CO(2) from SOC dust to the atmosphere and the contribution of SOC deposition to downwind C sinks.

Modeling dust emission response to North Atlantic millennial-scale climate variations from the perspective of East European MIS 3 loess deposits

Abstract. European loess sequences of the Marine Isotope Stage 3 (~60–25 kyr BP) show periods of strong dust accumulation alternating with episodes of reduced sedimentation, favoring soil development. In the western part of the loess belt centered around 50° N, these variations appear to have been related to the North Atlantic rapid climate changes: the Dansgaard–Oeschger (DO) and Heinrich (H) events. It has been recently suggested that the North Atlantic climate signal can be detected further east, in loess deposits from Stayky (50°05.65' N, 30°53.92' E), Ukraine. Here we use climate and dust emission modeling to investigate this data interpretation. We focus on the areas north and northeast of the Carpathians, where loess deposits can be found, and the corresponding main dust sources must have been located as well. The simulations were performed with the LMDZ atmospheric general circulation model and the ORCHIDEE land surface model. They represent a reference "Greenland stadial" state and two perturbations, seen as sensitivity tests with respect to changes in the North Atlantic surface conditions between 30° and 63° N: a "Greenland interstadial" and an "H event". The main source for the loess deposits in the studied area is identified as a dust deflation band, with two very active spots located west-northwest from our reference site. Emissions only occur between February and June. Differences from one deflation spot to another, and from one climate state to another, are explained by analyzing the relevant meteorological and surface variables. Over most of the source region, the annual emission fluxes in the "interstadial" experiment are 30 to 50% lower than the "stadial" values; they would only be about 20% lower if the inhibition of dust uplift by the vegetation were not taken into account. Assuming that lower emissions result in reduced dust deposition leads us to the conclusion that the loess–paleosol stratigraphic succession in the Stayky area reflects indeed North Atlantic millennial variations. In the main deflation areas of Western Europe, the vegetation effect alone determined most of the (~50% on average) stadial–interstadial flux differences. Even if its impact in Eastern Europe is less pronounced, this effect remains a key factor in modulating aeolian emissions at the millennial timescale. Conditions favorable to initiating particularly strong dust storms within a few hundred kilometers upwind from our reference site, simulated in the month of April of the H event experiment, support the correlation of H events with peaks in grain size index in some very detailed loess profiles, indicating increased coarse sedimentation.

THE DUST ENVIRONMENT OF MAIN-BELT COMET P/2012 T1 (PANSTARRS)

Main-Belt Comet P/2012 T1 (PANSTARRS) has been imaged using the 10.4m Gran Telescopio Canarias (GTC) and the 4.2m William Herschel Telescope (WHT) at six epochs in the period from November 2012 to February 2013, with the aim of monitoring its dust environment. The dust tails brightness and morphology are best interpreted in terms of a model of sustained dust emission spanning 4 to 6 months. The total dust mass ejected is estimated at $\sim$6--25$\times10^6$ kg. We assume a time-independent power-law size distribution function, with particles in the micrometer to centimeter size range. Based on the quality of the fits to the isophote fields, an anisotropic emission pattern is favored against an isotropic one, in which the particle ejection is concentrated toward high latitudes ($\pm45^\circ$ to $\pm90^\circ$) in a high obliquity object ($I$=80$^\circ$). This seasonally-driven ejection behavior, along with the modeled particle ejection velocities, are in remarkable agreement to those we found for P/2010 R2 (La Sagra) \citep{Moreno11a}.

The role of deep convection and nocturnal low-level jets for dust emission in summertime West Africa: Estimates from convection-permitting simulations.

[1] Convective cold pools and the breakdown of nocturnal low-level jets (NLLJs) are key meteorological drivers of dust emission over summertime West Africa, the world’s largest dust source. This study is the first to quantify their relative contributions and physical interrelations using objective detection algorithms and an off-line dust emission model applied to convection-permitting simulations from the Met Office Unified Model. The study period covers 25 July to 02 September 2006. All estimates may therefore vary on an interannual basis. The main conclusions are as follows: (a) approximately 40% of the dust emissions are from NLLJs, 40% from cold pools, and 20% from unidentified processes (dry convection, land-sea and mountain circulations); (b) more than half of the cold-pool emissions are linked to a newly identified mechanism where aged cold pools form a jet above the nocturnal stable layer; (c) 50% of the dust emissions occur from 1500 to 0200 LT with a minimum around sunrise and after midday, and 60% of the morning-to-noon emissions occur under clear skies, but only 10% of the afternoon-to-nighttime emissions, suggesting large biases in satellite retrievals; (d) considering precipitation and soil moisture effects, cold-pool emissions are reduced by 15%; and (e) models with parameterized convection show substantially less cold-pool emissions but have larger NLLJ contributions. The results are much more sensitive to whether convection is parameterized or explicit than to the choice of the land-surface characterization, which generally is a large source of uncertainty. This study demonstrates the need of realistically representing moist convection and stable nighttime conditions for dust modeling.Citation: Heinold, B., P. Knippertz, J. H. Marsham, S. Fiedler, N. S. Dixon, K. Schepanski, B. Laurent, and I. Tegen (2013), The role of deep convection and nocturnal low-level jets for dust emission in summertime West Africa: Estimates from convection-permitting simulations, J. Geophys. Res. Atmos., 118, 4385–4400, doi:10.1002/jgrd.50402.