Periodic Reporting for period 2 - FRAGMENT (FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe)
Reporting period: 2020-04-01 to 2021-09-30
The overarching goal of FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) is to understand, constrain and calculate the global mineralogical composition of dust along with its effects upon climate. FRAGMENT aims at fundamentally advancing the treatment of dust mineralogy by fulfilling several objectives: 1) It will contribute new fundamental understanding to reduce the large uncertainties in the emitted dust PSD and mineralogy by evaluating and extending current theoretical paradigms, based on an unprecedented ensemble of coordinated measurement campaigns and laboratory analyses. 2) Precise knowledge of dust mineral content requires more detailed and widespread measurements of soil mineralogy. We are evaluating airborne and spaceborne hyperspectral imaging to improve global atlases of soil mineralogy for dust modelling. The new methods and understanding will anticipate the coming innovation of retrieving soil mineralogy through high-quality spaceborne hyperspectral measurements. 3) While the impact of dust mineralogy upon climate is potentially large, the interconnection of mechanisms has been neglected in the few models that represent mineral variations. FRAGMENT will generate integrated and quantitative knowledge regarding the effects of dust mineral composition based on modelling experiments constrained with the theoretical innovations, field measurements and the new soil mineralogical map.
FRAGMENT is intimately linked to EMIT, a NASA instrument mission that will sample the Earth’s surface mineral composition using hyperspectral imaging spectroscopy on the International Space Station (ISS) by 2022. Analyses of all spectral data thus far include statistical principal component analyses and analyses of the depths of key absorption features indicative of different minerals, focusing on understanding the compositional diversity by grain size and geographic location. We are investigating correlations between spectral proxies for mineral abundance and results from XRD measurements. FRAGMENT is also extending Tetracorder, which is the key mineralogical mapping tool that is used in EMIT. We are developing three additional models beyond the default EMIT model that assumes that linear band depth is proportional mineral abundance. The four models have been coded and results are being refined by obtaining better optical constants. In a next step the models will be tested against laboratory spectra of known samples and applied to airborne spectroscopy data.
In terms of climate modelling, two models (MONARCH and EC-Earth3) are being further developed to include dependencies upon the dust mineralogical composition. We have enhanced and evaluated our MONARCH model with additional emission schemes and optical properties. We have also extended and implemented soil mineralogical maps using available data and quantified the associated uncertainties. We are using inversion modelling and data assimilation techniques to constrain the dust emission spatiotemporal variability. For future assimilation and evaluation work, we have co-developed new global estimates of dust optical depth. We have contributed to quantify for the first time the range in dust direct radiative effect at the top of the atmosphere due to current uncertainties in the surface soil mineralogy. We have also shown that part of the range of dust absorption retrieved from sun photometers can only be explained by regional variations in aerosol mineral composition.