The goal of J-WADI is to improve our fundamental understanding of the emission of desert dust, in particular its full-range size distribution and mineralogical composition. Desert dust aerosols are a key component of the Earth system. Created by wind erosion of arid and semi-arid surfaces, dust is the largest contributor to the global aerosol mass load and dominates climate effects over large areas of the Earth. Mineral dust from North Africa and the Middle East is frequently transported to Europe, especially in spring. Dust aerosols are a mixture of different minerals. Their relative abundances, particle size distribution, shape, surface topography and mixing state influence their effect upon climate.
Recent studies have shown that airborne dust particles can be larger than thought. Observations reveal that super-coarse (diameter between 10 and 63 μm) and even giant dust particles (diameter larger than 63 μm) can undergo long-range transport. As large particles not only scatter, but also absorb solar radiation, a misrepresentation of dust-aerosol size leads to biases in estimates of direct and indirect (related to clouds) radiative effects, making it uncertain whether dust has a net warming or cooling climate effect. Dust particles also affect cloud formation and large particles are expected to be particularly efficient. Super-coarse and giant dust particles are currently lacking in modeled dust loadings, because representations of gravitational settling would lead to quick fall-out. Besides dust settling, dust emission also suffers from shortcomings with regard to large particles. Dust emission schemes are normally calibrated against measurements that do not include particles larger than 20 μm and they are not designed to generate giant-particle emission.
Similarly, models typically assume that dust aerosols have a globally uniform composition, neglecting the known local and regional variations in the mineralogical composition of the dust sources. Current soil mineralogical maps are poorly constrained by observations, limiting their applicability. However, new global mineralogical maps based on high-quality spaceborne hyperspectral measurements will soon be available. In this context, a better understanding of the size-resolved mineralogical composition of dust and its relationship with the parent soil mineralogy is required to properly represent dust mineralogy in models. This would pave the way for a more nuanced and accurate representation of dust-cloud and dust-radiation interactions.
All in all, the inclusion of a wider dust particle-size range and dust mineralogical composition call for enhanced or novel parameterizations of dust emission and settling that facilitate entrainment and suspension in the entire size-spectrum and relate the emitted dust composition to the parent surface sediment. To underpin such new parameterizations, field measurements of dust including super-coarse and giant particles and their composition at the source of emission are required, as well as laboratory experiments on their interactions with clouds and radiation.
The main goals of J-WADI are to advance understanding of
- the mechanisms leading to the emission and continued suspension of super-coarse and giant dust particles
- the variability of the emitted dust particle-size distribution or the lack thereof
- the size-resolved mineralogy of dust at emission and its relationship with the parent soil
- the optical properties of the emitted dust
- the mineralogical composition of dust based on spectroscopy
J-WADI is linked to MICOS (Dust-induced ice nucleation: Effects of MIneralogical COmposition and Size), an joint ATMO-ACCESS project between the Barcelona Supercomputing Center and the Karlsruhe Institute of Technology (KIT). MICOS includes experiments with the renowned Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber.
J-WADI is also linked to EMIT, a NASA instrument mission that is sampling the Earth’s surface mineral composition using hyperspectral imaging spectroscopy on the International Space Station (ISS) since August 2022.