“Seeing” beneath the clouds - machine-learning-based reconstruction of
North African dust events
Abstract
Mineral dust is one of the most abundant atmospheric aerosol species and
has various far-reaching effects on the climate system and adverse
impacts on air quality. Satellite observations can provide
spatio-temporal information on dust emission and transport pathways.
However, satellite observations of dust plumes are frequently obscured
by clouds. We use a method based on established, machine-learning-based
image in-painting techniques to restore the spatial extent of dust
plumes for the first time. We train an artificial neural net (ANN) on
modern reanalysis data paired with satellite-derived cloud masks. The
trained ANN is applied to gray-scaled and cloud-masked false-color
daytime images for dust aerosols from 2021 and 2022, obtained from the
SEVIRI instrument onboard the Meteosat Second Generation satellite. We
find up to 15 \% of summertime observations in West
Africa and 10 \% of summertime observations in Nubia by
satellite images miss dust events due to cloud cover. The diurnal and
seasonal patterns in the reconstructed dust occurrence frequency are
consistent with known dust emission and transport processes. We use the
new dust-plume data to validate the operational forecasts provided by
the WMO Dust Regional Center in Barcelona from a novel perspective. The
comparison elucidates often similar dust plume patterns in the forecasts
and the satellite-based reconstruction, but the latter computation is
substantially faster. Our proposed reconstruction provides a new
opportunity for validating dust aerosol transport in numerical weather
models and Earth system models. It can be adapted to other aerosol
species and trace gases.