Dust Belt Research Articles

UV Index Forecasting under the Influence of Desert Dust: Evaluation against Surface and Satellite-Retrieved Data

Human exposure to healthy doses of UV radiation is required for vitamin D synthesis, but exposure to excessive UV irradiance leads to several harmful impacts ranging from premature wrinkles to dangerous skin cancer. However, for countries located in the global dust belt, accurate estimation of the UV irradiance is challenging due to a strong impact of desert dust on incoming solar radiation. In this work, a UV Index forecasting capability is presented, specifically developed for dust-rich environments, that combines the use of ground-based measurements of broadband irradiances UVA (320–400 nm) and UVB (280–315 nm), NASA OMI Aura satellite-retrieved data and the meteorology-chemistry mesoscale model WRF-Chem. The forecasting ability of the model is evaluated for clear sky days as well as during the influence of dust storms in Doha, Qatar. The contribution of UV radiation to the total incoming global horizontal irradiance (GHI) ranges between 5% and 7% for UVA and 0.1% and 0.22% for UVB. The UVI forecasting performance of the model is quite encouraging with an absolute average error of less than 6% and a correlation coefficient of 0.93. In agreement with observations, the model predicts that the UV Index at local noontime can drop from 10–11 on clear sky days to approximately 6–7 during typical dusty conditions in the Arabian Peninsula—an effect similar to the presence of extensive cloud cover.

Retrieving the global distribution of the threshold of wind erosion from satellite data and implementing it into the Geophysical Fluid Dynamics Laboratory land–atmosphere model (GFDL AM4.0/LM4.0)

Abstract. Dust emission is initiated when surface wind velocities exceed the threshold of wind erosion. Many dust models used constant threshold values globally. Here we use satellite products to characterize the frequency of dust events and land surface properties. By matching this frequency derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue aerosol products with surface winds, we are able to retrieve a climatological monthly global distribution of the wind erosion threshold (Vthreshold) over dry and sparsely vegetated surfaces. This monthly two-dimensional threshold velocity is then implemented into the Geophysical Fluid Dynamics Laboratory coupled land–atmosphere model (AM4.0/LM4.0). It is found that the climatology of dust optical depth (DOD) and total aerosol optical depth, surface PM10 dust concentrations, and the seasonal cycle of DOD are better captured over the “dust belt” (i.e., northern Africa and the Middle East) by simulations with the new wind erosion threshold than those using the default globally constant threshold. The most significant improvement is the frequency distribution of dust events, which is generally ignored in model evaluation. By using monthly rather than annual mean Vthreshold, all comparisons with observations are further improved. The monthly global threshold of wind erosion can be retrieved under different spatial resolutions to match the resolution of dust models and thus can help improve the simulations of dust climatology and seasonal cycles as well as dust forecasting.

P3420Is there an association between Saharan dust events and acute coronary syndrome incidence?

Abstract Background Asian dust and air pollution have been recently recognized as triggers in the incidence of acute myocardial infarction. The inflow of dust from the Sahara into Spain causes an increase in particulate matter (PM) levels in the atmosphere. The proximity to the Western Coast of Morocco and the Sahara Desert promotes the seasonality arrival of natural PM on the Canary Islands (Spain), leading to high concentrations of PM with an aerodynamic diameter over 10μm (PM10). The association of dust transport from the Sahara to the Atlantic Ocean and Mediterranean areas over the incidence of acute coronary syndromes (ACS), is unknown. Purpose The aim of the present study was to elucidate whether Saharan dust events in the dust belt - Canary Islands - is associated with the incidence of ACS. Methods We retrospectively collected data of hospitalizations due to ACS in 2416 consecutive patients from a tertiary care hospital in Tenerife (Canary Islands–Spain), from December 2012 to December 2017. Taking advantage of Canary Islands location, we characterized the Saharan dust events using PMx measurements and dust modeling. Concentrations of PM10 and reactive gases are measured in the Air Quality Network of the Canary Islands by using the European reference method. We applied the time-stratified case crossover design to examine the association between Saharan dust events and the incidence of ACS. This design allows us to adjust for individual confounders, season, time trend and the day of week. Using conditional Poisson regression models, we estimated the impact of PM10 Saharan dust events on the incidence of ACS. Because the effects of Saharan dust events could persist over the course of a few days, we examined the lag effect from Day 0 to Day 5. Results The occurrence of Saharan dust events observed 0–5 days before the ACS was not significantly associated with the incidence of ACS. PM10 (μg/m3) effect was: lag 0 (IRR: 0.999, 95% CI: 0.977–1.022), lag 1 (IRR: 1.025, 95% CI: 0.988–1.063), lag 2 (IRR: 0.98, 95% CI: 0.928–1.042), lag 3 (IRR: 0.976, 95% CI: 0.944–1.011), lag 4 (IRR: 0.996, 95% CI: 0.983–1.008) and lag 5 (IRR: 0.996, 95% CI: 0.984–1.007). (Figure 1) Poisson regression model of PM10 Conclusions This negative study, the first to assess the impact of Saharan dust events as a potential trigger in the onset of ACS, shows that African dust is unlikely to be associated with the incidence of ACS.

Functional metagenomic analysis of dust-associated microbiomes above the Red Sea

Atmospheric transport is a major vector for the long-range transport of microbial communities, maintaining connectivity among them and delivering functionally important microbes, such as pathogens. Though the taxonomic diversity of aeolian microorganisms is well characterized, the genomic functional traits underpinning their survival during atmospheric transport are poorly characterized. Here we use functional metagenomics of dust samples collected on the Global Dust Belt to initiate a Gene Catalogue of Aeolian Microbiome (GCAM) and explore microbial genetic traits enabling a successful aeolian lifestyle in Aeolian microbial communities. The GCAM reported here, derived from ten aeolian microbial metagenomes, includes a total of 2,370,956 non-redundant coding DNA sequences, corresponding to a yield of ~31 × 106 predicted genes per Tera base-pair of DNA sequenced for the aeolian samples sequenced. Two-thirds of the cataloged genes were assigned to bacteria, followed by eukaryotes (5.4%), archaea (1.1%), and viruses (0.69%). Genes encoding proteins involved in repairing UV-induced DNA damage and aerosolization of cells were ubiquitous across samples, and appear as fundamental requirements for the aeolian lifestyle, while genes coding for other important functions supporting the aeolian lifestyle (chemotaxis, aerotaxis, germination, thermal resistance, sporulation, and biofilm formation) varied among the communities sampled.

On the Properties of the Galactic Dust Layer within 700 pc of the Sun

We compare the spatial stellar color variations with our 3D model of the spatial dust distribution to refine the properties of the dust layer in Galactic solar neighborhoods. We use a complete sample of 93992 clump giants with an admixture of branch giants from the Gaia DR2 catalogue in a spatial cylinder with a radius of 700 pc around the Sun extending to |Z|=1800 pc. Accurate data of these stars in the Gaia DR2 GRP and WISE W3 bands have allowed the spatial GRP-W3 color variations to be used to calculate the model parameters and two characteristics of the sample, the mode of the dereddened color (GRP-W3)0 of the giant clump and the linear change of this mode with coordinate |Z|. As a result, an improved version of the three-dimensional model first proposed by Gontcharov (2009b) has been obtained. As in the previous version, the model suggests two dust layers, along the Galactic equator and in the Gould Belt, that intersect near the Sun at an angle of 18\pm2 degs. In contrast to the previous version of the model with a midplane of the Gould Belt dust layer in the form of a circle with the center at the Sun, in the new version this midplane is an ellipse decentered relative to the Sun. A scale height of 170\pm40 pc has been found for both dust layers. The modes of the absolute magnitude MW3=-1.70\pm0.02 and the dereddened color (GRP-W3)0=(1.43\pm0.01)-(0.020\pm0.007)|Z|, where Z is expressed in kpc, have been calculated for the giant clump near the Sun. The dispersions of the quantities under consideration have allowed the natural small-scale density fluctuations of the dust medium relative to the mean reddening calculated from the model to be characterized. These fluctuations make a major contribution to the uncertainty in the reddening.

Scientists Share Results of Dust Belt Research

Central Asian Dust Conference; Dushanbe, Tajikistan, 8–12 April 2019

Numerical simulation study on the coupling mechanism of composite-source airflow–dust field in a fully mechanized caving face

The dust produced during the process of coal mining is the main cause of the lung disease pneumoconiosis in miners. The study using Fluent software to perform a numerical study of the multi-source dust field in a fully mechanized caving face. The results of the simulation showed that the airflow velocities at the inlet and return air corners increase considerably, and that the overall air velocity in the coal mining face first decreases, from 2.33 to 0.41 m/s, before increasing to 1.91 m/s. The diffusion laws of dust produced by coal-cutting and the advancing of the hydraulic support at the working face tend to be consistent. Following dust superposition, a high-concentration dust belt is formed to the downwind side of the coal mining machine; this dust belt is about 16 m in length, about 1.2 m high, and with an average mass concentration of 1640 mg/m3.

Numerical Simulation of Dust Dispersion and Pollution in Breathing Zone of Fully Mechanized Mining Face

In order to more accurately analyze the law of dust escape in the position of breathing zone of fully mechanized coal face, a geometric model of fully mechanized coal face is established in 1205 fully mechanized coal face of Xinan Coal Mine. The movement law of dust with the wind field in the fully mechanized coal face is simulated by FLUENT software, and the dust in the area of breathing zone at different positions is also simulated. The situation is analyzed in detail. The simulation results show that the overall movement law of air flow in the whole working face is from small to large and then to small. When the air flow passes through the area near the shearer, the local space becomes smaller, the wind speed increases and transverse movement occurs. The dust produced by the shearer cutter diffuses into the space of the shearer and its downwind side roadway accompanied by the air flow. A high concentration dust belt is formed in the area near the shearer. The dust contaminated area in front of the Hydraulic support and the space breathing belt of the sidewalk increases gradually with the prolongation of dust production time and covers the height of the whole breathing belt after 80 s of dust production.

Variability and Trends in Dust Storm Frequency on Decadal Timescales: Climatic Drivers and Human Impacts

Dust storms present numerous hazards to human society and are particularly significant to people living in the Dust Belt which stretches from the Sahara across the Middle East to northeast Asia. This paper presents a review of dust storm variability and trends in frequency on decadal timescales from three Dust Belt settlements with long-term (>50 years) meteorological records: Nouakchott, Mauritania; Zabol, Iran, and Minqin, China. The inhabitants of each of these settlements have experienced a decline in dust storms in recent decades, since the late 1980s at Nouakchott, since 2004 at Zabol, and since the late 1970s at Minqin. The roles of climatic variables and human activities are assessed in each case, as drivers of periods of high dust storm frequency and subsequent declines in dust emissions. Both climatic and human variables have been important but overall the balance of research conclusions indicates natural processes (precipitation totals, wind strength) have had greater impact than human action, in the latter case both in the form of mismanagement (abandoned farmland, water management schemes) and attempts to reduce wind erosion (afforestation projects). Understanding the drivers of change in dust storm dynamics at the local scale is increasingly important for efforts to mitigate dust storm hazards as climate change projections suggest that the global dryland area is likely to expand in the twenty-first century, along with an associated increase in the risk of drought and dust emissions.

Direct radiative effect of dust–pollution interactions

Abstract. The chemical ageing of aeolian dust, through interactions with air pollution, affects the optical and hygroscopic properties of the mineral particles and hence their atmospheric residence time and climate forcing. Conversely, the chemical composition of the dust particles and their role as coagulation partners impact the abundance of particulate air pollution. This results in a change in the aerosol direct radiative effect that we interpret as an anthropogenic radiative forcing associated with mineral dust–pollution interactions. Using the ECHAM/MESSy atmospheric chemistry climate model (EMAC), which combines the Modular Earth Submodel System (MESSy) with the European Centre Hamburg (ECHAM) climate model, including a detailed parametrisation of ageing processes and an emission scheme accounting for the chemical composition of desert soils, we study the direct radiative forcing globally and regionally, considering solar and terrestrial radiation. Our results indicate positive and negative forcings, depending on the region. The predominantly negative forcing at the top of the atmosphere over large parts of the dust belt, from West Africa to East Asia, attains a maximum of about −2 W m−2 south of the Sahel, in contrast to a positive forcing over India. Globally averaged, these forcings partially counterbalance, resulting in a net negative forcing of −0.05 W m−2, which nevertheless represents a considerable fraction (40 %) of the total dust forcing.

Sub-millimetre non-contaminated detection of the disc around TWA 7 by ALMA

Debris disks can be seen as the left-overs of giant planet formation and the possible nurseries of rocky planets. While M-type stars out-number more massive stars we know very little about the time evolution of their circumstellar disks at ages older than $\sim 10$\,Myr. Sub-millimeter observations are best to provide first order estimates of the available mass reservoir and thus better constrain the evolution of such disks. Here, we present ALMA Cycle\,3 Band\,7 observations of the debris disk around the M2 star TWA\,7, which had been postulated to harbor two spatially separated dust belts, based on unresolved far-infrared and sub-millimeter data. We show that most of the emission at wavelengths longer than $\sim 300$\,$\mu$m is in fact arising from a contaminant source, most likely a sub-mm galaxy, located at about 6.6" East of TWA\,7 (in 2016). Fortunately, the high resolution of our ALMA data allows us to disentangle the contaminant emission from that of the disc and report a significant detection of the disk in the sub-millimeter for the first time with a flux density of 2.1$\pm$0.4 mJy at 870 $\mu$m. With this detection, we show that the SED can be reproduced with a single dust belt.

Vertical Structures of Dust Aerosols over East Asia Based on CALIPSO Retrievals

The spatiotemporal and especially the vertical distributions of dust aerosols play crucial roles in the climatic effect of dust aerosol. In the present study, the spatial-temporal distribution of dust aerosols over East Asia was investigated using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) retrievals (01/2007–12/2011) from the perspective of the frequency of dust occurrence (FDO), dust top layer height (TH) and profile of aerosol subtypes. The results showed that a typical dust belt was generated from the dust source regions (the Taklimakan and Gobi Deserts), in the latitude range of 25°N~45°N and reaching eastern China, Japan and Korea and, eventually, the Pacific Ocean. High dust frequencies were found over the dust source regions, with a seasonal sequence from high to low as follows: spring, summer, autumn and winter. Vertically, FDOs peaked at about 2 km over the dust source regions. In contrast, FDOs decreased with altitude over the downwind regions. On the dust belt from dust source regions to downwind regions, the dust top height (TH) was getting higher and higher. The dust TH varied in the range of 1.9–3.1 km above surface elevation (a.s.e.), with high values over the dust source regions and low values in the downwind areas, and a seasonally descending sequence of summer, spring, autumn and winter in accord with the seasonal variation of the boundary layer height. The annual AOD (Aerosol Optical Depth) was generally characterized by two high and two low AOD centers over East Asia. The percent contribution of the Dust Aerosol Optical Depth to the total AOD showed a seasonal variation from high to low as follows: spring, winter, autumn and summer. The vertical profile of the extinction coefficient revealed the predominance of pure dust particles in the dust source regions and a mixture of dust particles and pollutants in the downwind regions. The dust extinction coefficients over the Taklimakan Desert had a seasonal pattern from high to low as follows: spring, winter, summer and autumn. The results of the present study offered an understanding of the horizontal and vertical structures of dust aerosols over East Asia and can be used to evaluate the performance aerosol transport models.

Discriminating between clouds and aerosols in the CALIOP version 4.1 data products

Abstract. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Operations (CALIPSO) mission released version 4.1 (V4) of their lidar level 2 cloud and aerosol data products in November 2016. These new products were derived from the CALIPSO V4 lidar level 1 data, in which the calibration of the measured backscatter data at both 532 and 1064 nm was significantly improved. This paper describes updates to the V4 level 2 cloud–aerosol discrimination (CAD) algorithm that more accurately differentiate between clouds and aerosols throughout the Earth's atmosphere. The level 2 data products are improved with new CAD probability density functions (PDFs) that were developed to accommodate extensive calibration changes in the level 1 data. To enable more reliable identification of aerosol layers lofted into the upper troposphere and lower stratosphere, the CAD training dataset used in the earlier data releases was expanded to include stratospheric layers and representative examples of volcanic aerosol layers. The generic “stratospheric layer” classification reported in previous versions has been eliminated in V4, and cloud–aerosol classification is now performed on all layers detected everywhere from the surface to 30 km. Cloud–aerosol classification has been further extended to layers detected at single-shot resolution, which were previously classified by default as clouds. In this paper, we describe the underlying rationale used in constructing the V4 PDFs and assess the performance of the V4 CAD algorithm in the troposphere and stratosphere. Previous misclassifications of lofted dust and smoke in the troposphere have been largely improved, and volcanic aerosol layers and aerosol layers in the stratosphere are now being properly classified. CAD performance for single-shot layer detections is also evaluated. Most of the single-shot layers classified as aerosol occur within the dust belt, as may be expected. Due to changes in the 532 nm calibration coefficients, the V4 feature finder detects ∼9.0 % more features at night and ∼2.5 % more during the day. These features are typically weakly scattering and classified about equally as clouds and aerosols. For those tropospheric layers detected in both V3 and V4, the CAD classifications of more than 95 % of all cloud and daytime aerosol layers remain unchanged, as do the classifications of ∼89 % of nighttime aerosol layers. Overall, the nighttime net cloud and aerosol fractions remain unchanged from V3 to V4, but the daytime net aerosol fraction is increased by about 2 % and the daytime net cloud fraction is decreased by about 2 %.

Detection of scattered light from the hot dust in HD 172555

Context. Debris disks or belts are important signposts for the presence of colliding planetesimals and, therefore, for ongoing planet formation and evolution processes in young planetary systems. Imaging of debris material at small separations from the star is very challenging but provides valuable insights into the spatial distribution of the so-called hot dust produced by solid bodies located in or near the habitable zone. We report the first detection of scattered light from the hot dust around the nearby (d = 28.33 pc) A star HD 172555. Aims. We want to constrain the geometric structure of the detected debris disk using polarimetric differential imaging (PDI) with a spatial resolution of 25 mas and an inner working angle of about 0.1″. Methods. We measured the polarized light of HD 172555, with SPHERE/ZIMPOL, in the very broadband (VBB) or RI filter (λc = 735 nm, Δλ = 290 nm) for the projected separations between 0.08″ (2.3 au) and 0.77″ (22 au). We constrained the disk parameters by fitting models for scattering of an optically thin dust disk taking the limited spatial resolution and coronagraphic attenuation of our data into account. Results. The geometric structure of the disk in polarized light shows roughly the same orientation and outer extent as obtained from thermal emission at 18 μm. Our image indicates the presence of a strongly inclined (i ≈ 103.5°), roughly axisymmetric dust belt with an outer radius in the range between 0.3″ (8.5 au) and 0.4″ (11.3 au). An inner disk edge is not detected in the data. We derive a lower limit for the polarized flux contrast ratio for the disk of (Fpol)disk/F∗ > (6.2 ± 0.6) × 10−5 in the VBB filter. This ratio is small, only ~9%, when compared to the fractional infrared flux excess (≈ 7.2 × 10−4). The model simulations show that more polarized light could be produced by the dust located inside ≈2 au, which cannot be detected with the instrument configuration used. Conclusions. Our data confirm previous infrared imaging and provide a higher resolution map of the system, which could be further improved with future observations.

Tibetan Plateau Impacts on Global Dust Transport in the Upper Troposphere

Dust is a major component of atmospheric aerosol worldwide, greatly affecting regional and global climate. In this study dust aerosol optical depth (DAOD) and dust mass fluxes (DMF) were evaluated at different altitudes using measurements by the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) and ERA-Interim data from March through May (MAM) for the period 2007–16. Significantly higher upper-tropospheric (above ~8 km) dust loads and DMF downstream of the Tibetan Plateau (TP) relative to those over other major dust sources of the Northern Hemisphere were found during spring. A DMF magnitude of 1010 g integrated across a 2°-latitude segment during spring was estimated downstream of the TP in the upper troposphere. A dust belt can be clearly seen at altitudes higher than 6 km over the downwind direction of the TP at latitudes of around 30°–40°N, crossing the Pacific Ocean and extending to North America during spring. A pathway for transporting dust aerosols into the upper troposphere is proposed, as follows. Dust is uplifted to the midtroposphere over the source regions; then, frequent, deep, dry convection prevailing over the TP during spring can cause convective overshooting that uplifts the dust aerosols to the upper troposphere. The TP thus acts as a channel for transporting dust from the lower atmosphere to the upper troposphere, enabling the long-range zonal transport of dust around the Northern Hemisphere.

Detection of a Millimeter Flare from Proxima Centauri

Abstract We present new analyses of ALMA 12 m and Atacama Compact Array (ACA) observations at 233 GHz (1.3 mm) of the Proxima Centauri system with sensitivities of 9.5 and 47 μJy beam−1, respectively, taken from 2017 January 21 through April 25. These analyses reveal that the star underwent a significant flaring event during one of the ACA observations on 2017 March 24. The complete event lasted for approximately 1 minute and reached a peak flux density of 100 ± 4 mJy, nearly a factor of 1000 times brighter than the star’s quiescent emission. At the flare peak, the continuum emission is characterized by a steeply falling spectral index with frequency F ν ∝ ν α with α = −1.77 ± 0.45, and a lower limit on the fractional linear polarization of . Because the ACA observations do not show any quiescent excess emission, we conclude that there is no need to invoke the presence of a dust belt at 1–4 au. We also posit that the slight excess flux density of 101 ± 9 μJy observed in the 12 m observations, compared to the photospheric flux density of 74 ± 4 μJy extrapolated from infrared wavelengths, may be due to coronal heating from continual smaller flares, as is seen for AU Mic, another nearby well-studied M dwarf flare star. If this is true, then the need for warm dust at ∼0.4 au is also removed.

Shaping HR8799’s outer dust belt with an unseen planet

HR8799 is a benchmark system for direct imaging studies. It hosts two debris belts, which lie internally and externally to four giant planets. This paper considers how the four known planets and a possible fifth planet, interact with the external population of debris through N-body simulations. We find that when only the known planets are included, the inner edge of the outer belt predicted by our simulations is much closer to the outermost planet than recent ALMA observations suggest. We subsequently include a fifth planet in our simulations with a range of masses and semi-major axes, which is external to the outermost known planet. We find that a fifth planet with a mass and semi-major axis of 0.1$\mathrm{M_J}$ and 138au predicts an outer belt that agrees well with ALMA observations, whilst remaining stable for the lifetime of HR8799 and lying below current direct imaging detection thresholds. We also consider whether inward scattering of material from the outer belt can input a significant amount of mass into the inner belt. We find that for the current age of HR8799, only $\sim$1\% of the mass loss rate of the inner disk can be replenished by inward scattering. However we find that the higher rate of inward scattering during the first $\sim$10Myr of HR8799 would be expected to cause warm dust emission at a level similar to that currently observed, which may provide an explanation for such bright emission in other systems at $\sim10$Myr ages.

In situ observations of dust particles in Martian dust belts using a large-sensitive-area dust sensor

In order to determine whether Martian dust belts (ring or torus) actually exist and, if so, to determine the characteristics of the dust, we propose a Circum-Martian Dust Monitor (CMDM) to be deployed on the Martian Moons Exploration (MMX) project, in which JAXA plans to launch the spacecraft in 2024, investigate Phobos and Deimos, and return samples back to Earth. The CMDM is a newly developed instrument that is an impact dust detector. It weighs only 650 g and has a sensor aperture area of ∼1 m2, according to the conceptual design study. Detectable velocities (v) range from 0.5 km/s to more than 70 km/s, which will cover all possible dust particles: circummartian (low v), interplanetary (mid v), and interstellar (high v) particles. The measurable mass ranges from 1.3 × 10−9 g to 7.8 × 10−7 g at v = 0.5 km/s. Since the MMX spacecraft will take a quasi-circular, prograde orbit around Mars, the CMDM will be able to investigate particles from Phobos and Deimos with relative velocities lower than 1 km/s. Therefore, the CMDM will be able to determine whether or not a confined dust ring exists along Phobos' orbit and whether an extended dust torus exists along Deimos' orbit. It may also be able to clarify whether or not any such ring or torus are self-sustained.

Infrared dust aerosol optical depth retrieved daily from IASI and comparison with AERONET over the period 2007–2016

Aerosols represent one of the dominant uncertainties in radiative forcing, partly because of their very high spatiotemporal variability, a still insufficient knowledge of their microphysical and optical properties, or of their vertical distribution. A better understanding and forecasting of their impact on climate therefore requires precise observations of dust emission and transport. Observations from space offer a good opportunity to follow, day by day and at high spatial resolution, dust evolution at global scale and over long time series. Infrared observations allow retrieving dust aerosol optical depth (AOD) as well as the mean dust layer altitude, daytime and nighttime, over oceans and over continents, in particular over desert. Moreover, coarse mode particles are preferentially observed in the infrared, when, in the visible, both larger and finer particles are observed making the distinction between the two modes difficult. Therefore, they appear complementary to observations in the visible. In this study, a decade of the Infrared Atmospheric Sounder Interferometer (IASI) on board European Satellite Metop-A observations, from July 2007 to December 2016, has been processed pixel by pixel, using a “Look-Up-Table” (LUT) physical approach. Important improvements have been brought to our former approach in order to extend it to: 1) daytime retrieval, 2) mid-latitude retrieval, 3) retrieval at the IASI pixel resolution, 4) near real time retrieval (day-1). Moreover, over continents, surface characteristics (pressure, temperature, as well as emissivity spectrum) are now better accounted for. Here, a particular attention is given to the validation of the IASI-retrieved AOD through comparisons with the Spectral Deconvolution Algorithm (SDA) 500nm coarse mode AOD observed at 70 ground-based Aerosol RObotic NETwork (AERONET) sites during the 114months processed. Even if such a comparison requires converting AOD from infrared to visible, inherently leading to significant uncertainties, the two AOD datasets compare well, with an overall correlation of 0.8. For a large majority of sites, correlation ranges from 0.7 to 0.9. Sites with highest correlation are well distributed within the “dust belt” (Sahara, Arabian Peninsula, Mediterranean basin, India and also the Caribbean). Correlations obtained for East-Asia are in general smaller, which might be due to a more complex dust structure (i.e., impact of pollution) and partly due to an increase of the AERONET coarse-mode AOD uncertainty. More generally, the good overall agreement between our restitutions and AERONET AOD demonstrates the ability of infrared sounders to infer dust properties, which opens interesting perspective for a synergy with visible observations.

ALMA Discovery of Dust Belts around Proxima Centauri

Abstract Proxima Centauri, the star closest to our Sun, is known to host at least one terrestrial planet candidate in a temperate orbit. Here we report the Atacama Large Millimeter/submillimeter Array (ALMA) detection of the star at 1.3 mm wavelength and the discovery of a belt of dust orbiting around it at distances ranging between 1 and 4 au, approximately. Given the low luminosity of the Proxima Centauri star, we estimate a characteristic temperature of about 40 K for this dust, which might constitute the dust component of a small-scale analog to our solar system’s Kuiper Belt. The estimated total mass, including dust and bodies up to 50 km in size, is of the order of 0.01 Earth masses, which is similar to that of the solar Kuiper Belt. Our data also show a hint of warmer dust closer to the star. We also find signs of two additional features that might be associated with the Proxima Centauri system that still require further observations to be confirmed: an outer extremely cold (about 10 K) belt around the star at about 30 au, with an orbital plane that is tilted about 45° with respect to the plane of the sky; additionally, we marginally detect a compact 1.3 mm emission source at a projected distance of about 1.2 arcsec from the star, the nature of which is still unknown.