scholarly journals The fate of saharan dust across the atlantic and implications for a central american dust barrier

2011 ◽  
Vol 11 (16) ◽  
pp. 8415-8431 ◽  
Author(s):  
E. Nowottnick ◽  
P. Colarco ◽  
A. da Silva ◽  
D. Hlavka ◽  
M. McGill
Keyword(s):  
Central America ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Saharan Dust ◽  
Sensitivity Analyses ◽  
Transport Barrier ◽  
Dust Transport ◽  
Transport Dynamics ◽  
The Caribbean ◽  
Wet Removal

Abstract. Saharan dust was observed over the Caribbean basin during the summer 2007 NASA Tropical Composition, Cloud, and Climate Coupling (TC4) field experiment. Airborne Cloud Physics Lidar (CPL) and satellite observations from MODIS suggest a barrier to dust transport across Central America into the eastern Pacific. We use the NASA GEOS-5 atmospheric transport model with online aerosol tracers to perform simulations of the TC4 time period in order to understand the nature of this barrier. Our simulations are driven by the Modern Era Retrospective-Analysis for Research and Applications (MERRA) meteorological analyses. Compared to observations from MODIS and CALIOP, GEOS-5 reproduces the observed location and magnitude of observed dust events, but our baseline simulation does not develop as strong a barrier to dust transport across Central America as observations suggest. Analysis of the dust transport dynamics and loss processes suggest that while both mechanisms play a role in defining the dust transport barrier, loss processes by wet removal of dust are about twice as important as transport. Sensitivity analyses with our model showed that the dust barrier would not exist without convective scavenging over the Caribbean. The best agreement between our model and the observations was obtained when dust wet removal was parameterized to be more aggressive, treating the dust as we do hydrophilic aerosols.

scholarly journals The fate of Saharan dust across the Atlantic and implications for a Central American dust barrier

2011 ◽  
Vol 11 (3) ◽  
pp. 8337-8384 ◽  
Author(s):  
E. Nowottnick ◽  
P. Colarco ◽  
A. da Silva ◽  
D. Hlavka ◽  
M. McGill
Keyword(s):  
Central America ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Saharan Dust ◽  
Sensitivity Analyses ◽  
Transport Barrier ◽  
Dust Transport ◽  
Transport Dynamics ◽  
The Caribbean ◽  
Wet Removal

Abstract. Saharan dust was observed over the Caribbean basin during the summer 2007 NASA Tropical Composition, Cloud, and Climate Coupling (TC4) field experiment. Airborne Cloud Physics Lidar (CPL) and satellite observations from MODIS suggest a barrier to dust transport across Central America into the eastern Pacific. We use the NASA GEOS-5 atmospheric transport model with online aerosol tracers to perform simulations of the TC4 time period in order to understand the nature of this barrier. Our simulations are driven by the Modern Era Retrospective-Analysis for Research and Applications (MERRA) meteorological analyses. We evaluate our baseline simulated dust distributions using MODIS and CALIOP satellite and ground-based AERONET sun photometer observations. GEOS-5 reproduces the observed location, magnitude, and timing of major dust events, but our baseline simulation does not develop as strong a barrier to dust transport across Central America as observations suggest. Analysis of the dust transport dynamics and lost processes suggest that while both mechanisms play a role in defining the dust transport barrier, loss processes by wet removal of dust are about twice as important as transport. Sensitivity analyses with our model showed that the dust barrier would not exist without convective scavenging over the Caribbean. The best agreement between our model and the observations was obtained when dust wet removal was parameterized to be more aggressive, treating the dust as we do hydrophilic aerosols.

scholarly journals Compositional changes of present-day transatlantic Saharan dust deposition

2016 ◽  
Author(s):  
Laura F. Korte ◽  
Geert-Jan Brummer ◽  
Michèlle van der Does ◽  
Catarina V. Guerreiro ◽  
Rick Hennekam ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Sediment Trap ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Saharan Dust ◽  
The West ◽  
Dust Transport ◽  
Mass Fluxes ◽  
The Caribbean ◽  
Particle Fluxes

Abstract. Massive amounts of Saharan dust are blown from the African coast across the Atlantic Ocean towards the Americas each year. This dust has, depending on its chemistry, direct and indirect effects on global climate including reflection and absorption of solar radiation as well as transport and deposition of nutrients and metals fertilizing both ocean and land. To determine the temporal and spatial variability of Saharan dust transport and deposition and their marine environmental effects across the equatorial North Atlantic Ocean, we have set up a monitoring experiment using deep-ocean sediment traps as well as land-based dust collectors. The sediment traps were deployed at five ocean sites along a transatlantic transect between northwest Africa and the Caribbean along 12⁰ N, in a down-wind extension of the land-based dust collectors placed at 19⁰ N on the Mauritanian coast in Iwik. In this paper, we lay out the setup of the monitoring experiment and present the particle fluxes from sediment trap sampling over 24 continuous and synchronised intervals from October 2012 through to November 2013. We establish the temporal distribution of the particle fluxes deposited in the Atlantic and compare chemical compositions with the land-based dust collectors propagating to the down-wind sediment trap sites, and with satellite observations of Saharan dust outbreaks. First-year results show that the total mass fluxes in the ocean are highest at the sampling sites in the east and west, closest to the African continent and the Caribbean, respectively. Element ratios reveal that the lithogenic particles deposited nearest to Africa are most similar in composition to the Saharan dust collected in Iwik. Down-wind increasing Al, Fe and K contents suggest a downwind change in the mineralogical composition of Saharan dust and indicate an increasing contribution of clay minerals towards the west. In the westernmost Atlantic, admixture of re-suspended clay-sized sediments advected towards the deep sediment trap cannot be excluded. Seasonality is most prominent near both continents but generally weak, with mass fluxes dominated by calcium carbonate and clear seasonal maxima of biogenic silica towards the west. The monitoring experiment is now extended with autonomous dust sampling buoys for better quantification Saharan dust transport and deposition from source to sink and its impact on fertilization and carbon export to the deep ocean.

scholarly journals Downward particle fluxes of biogenic matter and Saharan dust across the equatorial North Atlantic

2017 ◽  
Vol 17 (9) ◽  
pp. 6023-6040 ◽  
Author(s):  
Laura F. Korte ◽  
Geert-Jan A. Brummer ◽  
Michèlle van der Does ◽  
Catarina V. Guerreiro ◽  
Rick Hennekam ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Sediment Trap ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Saharan Dust ◽  
Dust Transport ◽  
Mass Fluxes ◽  
The Caribbean ◽  
Particle Fluxes

Abstract. Massive amounts of Saharan dust are blown from the coast of northern Africa across the Atlantic Ocean towards the Americas each year. This dust has, depending on its chemistry, direct and indirect effects on global climate which include reflection and absorption of solar radiation as well as transport and deposition of nutrients and metals fertilizing both ocean and land. To determine the temporal and spatial variability of Saharan dust transport and deposition and their marine environmental effects across the equatorial North Atlantic Ocean, we have set up a monitoring experiment using deep-ocean sediment traps as well as land-based dust collectors. The sediment traps were deployed at five ocean sites along a transatlantic transect between north-west Africa and the Caribbean along 12° N, in a downwind extension of the land-based dust collectors placed at 19° N on the Mauritanian coast in Iouîk. In this paper, we lay out the setup of the monitoring experiment and present the particle fluxes from sediment trap sampling over 24 continuous and synchronized intervals from October 2012 through to November 2013. We establish the temporal distribution of the particle fluxes deposited in the Atlantic and compare chemical compositions with the land-based dust collectors propagating to the downwind sediment trap sites, and with satellite observations of Saharan dust outbreaks. First-year results show that the total mass fluxes in the ocean are highest at the sampling sites in the east and west, closest to the African continent and the Caribbean, respectively. Element ratios reveal that the lithogenic particles deposited nearest to Africa are most similar in composition to the Saharan dust collected in Iouîk. Downwind increasing Al, Fe and K contents suggest a downwind change in the mineralogical composition of Saharan dust and indicate an increasing contribution of clay minerals towards the west. In the westernmost Atlantic Ocean, admixture of re-suspended clay-sized sediments advected towards the deep sediment trap cannot be excluded. Seasonality is most prominent near both continents but generally weak, with mass fluxes dominated by calcium carbonate and clear seasonal maxima of biogenic silica towards the west. The monitoring experiment is now extended, with autonomous dust sampling buoys for better quantification of Saharan dust transport and deposition from source to sink and their impact on fertilization and carbon export to the deep ocean.

scholarly journals Transatlantic Saharan dust transport: Model simulation and results

2006 ◽  
Vol 111 (D9) ◽  
Author(s):  
George Kallos ◽  
Anastasios Papadopoulos ◽  
Petros Katsafados ◽  
Slobodan Nickovic
Keyword(s):  
Transport Model ◽  
Model Simulation ◽  
Saharan Dust ◽  
Dust Transport

scholarly journals Dust transport and horizontal fluxes measurement with spaceborne lidars ALADIN, CALIOP and model reanalysis data

2021 ◽  
Author(s):  
Guangyao Dai ◽  
Kangwen Sun ◽  
Xiaoye Wang ◽  
Songhua Wu ◽  
Xiangying E ◽  
...  
Keyword(s):  
Optical Properties ◽  
Atlantic Ocean ◽  
Caribbean Sea ◽  
Saharan Dust ◽  
Trade Wind ◽  
Development Phase ◽  
Dust Event ◽  
Dust Transport ◽  
The Caribbean ◽  
Emission Phase

Abstract. In this paper, a long-term large-scale Sahara dust transport event occurred during 14 June and 27 June 2020 is tracked with the spaceborne lidars ALADIN and CALIOP observations and the models ECMWF and HYSPLIT analysis. We evaluate the performance of the ALADIN and CALIOP on the observations of dust optical properties and wind fields and explore the capability in tracking the dust events and in calculating the dust horizontal mass fluxes with the combination of measurement data from ALADIN and CALIOP coupled with the products from ECMWF and HYSPLIT. Compared with the traditional assessments based on the data from CALIOP and models, the complement of Aeolus-produced aerosol optical properties and wind data will significantly improve the accuracy of dust horizontal flux estimations. The dust plumes are identified with AIRS/Aqua Dust Score Index and with the Vertical Feature Mask products from CALIPSO. The emission, dispersion, transport and deposition of the dust event are monitored using the data from HYSPLIT, CALIPSO and AIRS/Aqua. With the quasi-synchronization observations by ALADIN and CALIOP, combining the wind vectors and relative humidity, the dust horizontal fluxes are calculated. From this study, it is found that the dust event generated on 14 and 15 June 2020 from Sahara Desert in North Africa, and then dispersed and transported westward over the Atlantic Ocean, and finally deposited in the Atlantic Ocean, the Americas and the Caribbean Sea. During the transport and deposition processes, the dust plumes are trapped in the Northeasterly Trade-wind zone between the latitudes of 5° N and 30° N and altitudes of 0 km and 6 km (in this paper we name this space area as “Saharan dust eastward transport tunnel”). From the measurement results on 19 June 2020, influenced by the hygroscopic effect and mixing with other types aerosols, the backscatter coefficients of dust plumes are increasing along the transport routes, with 3.88 × 10−6 ± 2.59 × 10−6 m−1 sr−1 in “dust portion during emission phase”, 7.09 × 10−6 ± 3.34 × 10−6 m−1 sr−1 in “dust portion during development phase” and 7.76 × 10−6 ± 3.74 × 10−6 m−1 sr−1 in “dust portion during deposition phase”. Finally, the horizontal fluxes at different dust parts and heights on 19 June and on entire transport routine during transportation are computed. On 19 June, the dust horizontal fluxes are about 2.17 ± 1.83 mg m−2 s−1 in dust portion during emission phase, 2.72 ± 1.89 mg m−2 s−1 in dust portion during development phase and 3.01 ± 2.77 mg m−2 s−1 in dust portion during deposition phase. In the whole life-time of the dust event, the dust horizontal fluxes are about 1.30 ± 1.07 mg m−2 s−1 on 15 June 2020, 2.62 ± 1.88 mg m−2 s−1 on 16 June 2020, 2.72 ± 1.89 mg m−2 s−1 on 19 June 2020, 1.98 ± 1.41 mg m−2 s−1 on 24 June 2020 and 2.11 ± 1.74 mg m−2 s−1 on 27 June 2020. From this study, it is found that the minimum of the fluxes appears when the dust event is initially generated on 15 June. During the dust development stage, the horizontal fluxes gradually increase and reach to the maximum value on 19 June with the enhancement of the dust event. Then, the horizontal fluxes gradually decrease since most of the dust deposited in the Atlantic Ocean, the Americas and the Caribbean Sea. Combining the Chlorophyll concentrations data provided by MODIS-Aqua, the Saharan Dust is found transported across the oligotrophic regions Atlantic Ocean towards the Americas and Caribbean Sea, which are also oligotrophic regions. The mineral dust delivers micronutrients including soluble Fe and P to the deposition zones and has the potential to fertilizing the ocean and increase the primary productivity in the Atlantic Ocean and Caribbean Sea.

scholarly journals Global modelling of soil carbonyl sulfide exchange

2021 ◽  
Author(s):  
Camille Abadie ◽  
Fabienne Maignan ◽  
Marine Remaud ◽  
Jérôme Ogée ◽  
J. Elliott Campbell ◽  
...  
Keyword(s):  
Land Surface ◽  
Latitudinal Gradient ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Carbonyl Sulfide ◽  
Sensitivity Analyses ◽  
Surface Model ◽  
Small Magnitude ◽  
C Cycle ◽  
The Impact

Abstract. Carbonyl sulfide (COS) is an atmospheric trace gas of interest for C cycle research because COS uptake by continental vegetation is strongly related to terrestrial gross primary productivity (GPP), the largest and most uncertain flux in atmospheric CO2 budgets. However, to use atmospheric COS budgets as an additional tracer of GPP, an accurate quantification of COS exchange by soils is also needed. At present, the atmospheric COS budget is unbalanced globally, with total COS flux estimates from oxic and anoxic soils that vary between −409 and −104 GgS yr−1. This uncertainty hampers the use of atmospheric COS concentrations to constrain GPP estimates through atmospheric transport inversions. In this study we implemented a mechanistic soil COS model in the ORCHIDEE land surface model to simulate COS fluxes in oxic and anoxic soils. Evaluation of the model against flux measurements at 7 sites yields a mean root mean square deviation of 1.6 pmol m−2 s−1, instead of 2 pmol m−2 s−1 when using a previous empirical approach that links soil COS uptake to soil heterotrophic respiration. The new model predicts that, globally and over the 2009–2016 period, oxic soils act as a net uptake of −126 GgS yr−1, and anoxic soils are a source of +96 GgS yr−1, leading to a global net soil sink of only −30 GgS yr−1, i.e., much smaller than previous estimates. The small magnitude of the soil fluxes suggests that the error in the COS budget is dominated by the much larger fluxes from plants, oceans, and industrial activities. The predicted spatial distribution of soil COS fluxes, with large emissions in the tropics from oxic (up to 68.2 pmol COS m−2 s−1) and anoxic (up to 36.8 pmol COS m−2 s−1) soils, marginally improves the latitudinal gradient of atmospheric COS concentrations, after transport by the LMDZ atmospheric transport model. The impact of different soil COS flux representations on the latitudinal gradient of the atmospheric COS concentrations is strongest in the northern hemisphere. We also implemented spatio-temporal variations of near-ground atmospheric COS concentrations in the modelling of biospheric COS fluxes, which helped reduce the imbalance of the atmospheric COS budget by lowering COS uptake by soils and vegetation globally (−10 % for soil, and −8 % for vegetation with a revised mean estimate of −576 GgS y−r1 over 2009–2016). Sensitivity analyses highlighted the different parameters to which each soil COS flux model is the most responsive, selected in a parameter optimization framework. Having both vegetation and soil COS fluxes modelled within ORCHIDEE opens the way for using observed ecosystem COS fluxes and larger scale atmospheric COS mixing ratios to improve the simulated GPP, through data assimilation techniques.

Local Histories/Global Designs

2012 ◽  
Author(s):  
Walter D. Mignolo
Keyword(s):  
Social Sciences ◽  
Central America ◽  
Postcolonial Studies ◽  
The United States ◽  
Philosophy Of History ◽  
South Central ◽  
The Social ◽  
The Caribbean ◽  
Border Thinking ◽  
East West

This book is an extended argument about the “coloniality” of power. In a shrinking world where sharp dichotomies, such as East/West and developing/developed, blur and shift, this book points to the inadequacy of current practices in the social sciences and area studies. It explores the crucial notion of “colonial difference” in the study of the modern colonial world and traces the emergence of an epistemic shift, which the book calls “border thinking.” Further, the book expands the horizons of those debates already under way in postcolonial studies of Asia and Africa by dwelling on the genealogy of thoughts of South/Central America, the Caribbean, and Latino/as in the United States. The book's concept of “border gnosis,” or sensing and knowing by dwelling in imperial/colonial borderlands, counters the tendency of occidentalist perspectives to manage, and thus limit, understanding. A new preface discusses this book as a dialogue with Hegel's Philosophy of History.

Sign in / Sign up

Export Citation Format

Share Document