Constraining dust-driver relationships in global climate models using remote sensing observations over Australia

Abstract

Mineral dust is the most abundant aerosol by dry mass in the Earth’s atmosphere. Its interactions with our planet are wide-ranging and multidisciplinary in nature. It plays an important role in maintaining the net radiation budget of our planet by scattering and absorbing short and long-wave radiation, affecting cloud microphysics, and fertilizing distant ecosystems. Airborne mineral dust may also present a hazard to human health by decreasing air quality and acting as a catalyst to disease spread. However, due to the complexity of interactions, forcings, and feedbacks in which dust is involved, researchers are unsure of whether the increased dust loading over the past century has encouraged or hindered climate changes. It is crucial that researchers understand what changes may emerge in the future because of enhanced dust emissions in order to help inform environmental policy at both local and global levels. As a first stage in this thesis, satellite retrievals of aerosol optical depth (AOD) from two distinct algorithms, MAIAC and DB, are evaluated over a 20-year period (2001-2020 inclusive) to determine the suitability of each for deriving a climatology of Australian dust activity. Whilst both algorithms can retrieve AOD to a good standard, it is found that MAIAC slightly outperforms DB, although both algorithms show better performance over vegetated surfaces and reduced performance over land surfaces classed as bare. Following this, two databases of dust optical depth (DOD) are derived from MAIAC and DB and subsequently evaluated against ground truth, with the comparative advantages of each discussed. These dust observations are used as a basis to evaluate dust in the UKESM family of global climate models. In-depth testing and analysis of the key drivers of dust activity reveal that near-surface wind speeds and top-layer soil moisture are critical in simulating the observed interannual variability of DOD in Australia.