Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment

Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment
Name	Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment
Location	Sahara Desert; Atlantic Ocean; Canary Islands

Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment The Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment was a coordinated field campaign that investigated mineral dust emission from the Sahara Desert, transatlantic transport across the Atlantic Ocean, and interactions with cloud systems affecting regions such as the Canary Islands and the Caribbean. The campaign brought together researchers from institutions including National Aeronautics and Space Administration, European Space Agency, National Oceanic and Atmospheric Administration, and multiple universities to combine airborne, ship-based, and ground-based measurements with satellite remote sensing and numerical modeling. The experiment aimed to quantify dust source processes, long-range transport pathways, aerosol optical properties, and aerosol-cloud interactions to improve predictive capabilities for weather, climate, and air quality.

Background and Objectives

The campaign built on prior programs such as ACE-2, SAMUM, AMMA, and Dust Observations from the Mediterranean to the North Atlantic (DOMENA) to address unresolved questions about dust uplift in the Harmattan, lofting mechanisms over the Sahara Desert, and export by the African Easterly Jet and trade winds. Primary objectives included characterizing emission fluxes at source regions near Bodélé Depression and Mauritania, determining aerosol size distribution and mineralogy relevant to radiative forcing studies referenced by the Intergovernmental Panel on Climate Change, and constraining aerosol indirect effects on cloud microphysics observed over the Atlantic Ocean and the Caribbean Sea. Collaborations involved agencies such as US Geological Survey, Met Office, Max Planck Institute for Chemistry, and research programs funded by the European Commission.

Experimental Design and Instrumentation

The experiment used instrument suites similar to those deployed in CALIPSO-era studies and incorporated airborne platforms like research aircraft from NASA Armstrong Flight Research Center and Deutsches Zentrum für Luft- und Raumfahrt alongside ships from NOAA Ship Ronald H. Brown and coastal sites on Lanzarote and Tenerife. In situ probes included optical particle counters, aerodynamic particle sizers, and cascade impactors for mineralogical analysis comparable to techniques used at Scripps Institution of Oceanography and Lamont–Doherty Earth Observatory, while remote sensors included sunphotometers in the AERONET network and lidar systems akin to EARLINET deployments. Instruments for cloud microphysics featured cloud droplet probes used in studies by National Center for Atmospheric Research and radiometers like those developed at European Centre for Medium-Range Weather Forecasts facilities.

Field Campaign Operations and Data Collection

Field operations were coordinated through command centers similar to those used in INTEX and VOCALS campaigns, with flight planning informed by forecasts from ECMWF and GFS model output and satellite observations from MODIS, SEVIRI, and CALIPSO. Ship transects sampled plume evolution from near-source regions off Dakar to downwind locations near Barbados while ground stations on islands collected continuous aerosol optical depth and chemical speciation data. Ancillary datasets included radiosonde releases in patterns established by RAOB programs and ozonesonde measurements modeled after WOUDC protocols to assess photochemical impacts noted in studies by Harvard University and MIT.

Modeling and Data Analysis Methods

Data assimilation and transport analyses used Eulerian and Lagrangian frameworks implemented in models like WRF, GOCART, and GEOS-Chem with emissions constrained by satellite retrievals from OMI and surface reflectance data from Copernicus products. Microphysical process evaluation employed cloud-resolving models and parameterizations similar to those in CAM5 and techniques developed at NOAA GFDL, while radiative transfer calculations used tools comparable to RRTMG and spectrally resolved models from NASA Goddard. Source attribution applied trajectory analysis methodologies based on HYSPLIT and receptor modeling analogues used in EPA receptor studies, integrating mineralogical fingerprinting approaches from USGS and isotopic tracing methods pioneered at Columbia University.

Key Findings and Scientific Results

The experiment produced quantitative estimates of dust emission fluxes that refined source strength assessments for regions like Bodélé Depression and coastal Mauritania, demonstrated frequent lofting into the mid-troposphere by convective systems influenced by the African Easterly Wave, and documented long-range transport episodes reaching the Caribbean and Amazon Basin. Observations confirmed substantial aerosol radiative forcing at both shortwave and longwave bands consistent with results reported by IPCC AR5 assessments, and showed modification of cloud droplet number concentrations and cloud albedo in marine stratocumulus regimes akin to findings from CLARIFY and RICO. Mineralogical analyses linked iron-bearing dust to potential fertilization effects in ocean biogeochemistry studies related to GEOTRACES and productivity shifts observed by BATS and HOT programs.

Impacts on Weather, Climate, and Air Quality

Results informed improved representation of dust in operational forecasts at Met Office and NOAA centers, reducing biases in radiative heating profiles and convective initiation associated with dust radiative effects studied in Monsoon dynamics. Air quality implications included elevated particulate matter concentrations downwind affecting public health assessments guided by World Health Organization criteria and exacerbating aerosol–ozone chemistry interactions reported in Tropospheric Chemistry studies. Climatic implications encompassed forcing contributions to regional energy budgets and potential modulation of precipitation patterns over the Sahel and adjacent ocean basins, reinforcing linkages explored in CMIP6 model intercomparisons.

Legacy, Data Availability, and Ongoing Research

The campaign legacy includes open-access datasets archived in repositories patterned after NASA EarthData and PANGAEA standards, integration with long-term networks such as AERONET and EARLINET, and follow-on studies by groups at Imperial College London, ETH Zurich, and University of Miami. Ongoing research leverages the dataset for improved aerosol–cloud parameterizations in CMIP7-era experiments, continues mineral dust source attribution using approaches from Machine Learning applications at Google DeepMind-affiliated research, and supports interdisciplinary work linking dust transport to marine ecology initiatives like SOCCOM and paleoclimate reconstructions used by NOAA Paleoclimatology programs. Category:Atmospheric sciences