Modelling the 2021 East Asia super dust storm using FLEXPART and FLEXDUST and its comparison with reanalyses and observations

The 2021 East Asia sandstorm began from the Eastern Gobi desert steppe in Mongolia on March 14, and later spread to northern China and the Korean Peninsula. It was the biggest sandstorm to hit China in a decade, causing severe air pollution and a significant threat to human health. Capturing and predicting such extreme events is critical for society. The Lagrangian particle dispersion model FLEXPART and the associated dust emission model FLEXDUST have been recently developed and applied to simulate global dust cycles. However, how well the model captures Asian dust storm events remains to be explored. In this study, we applied FLEXPART to simulate the recent 2021 East Asia sandstorm, and evaluated its performance comparing with observation and observation-constrained reanalysis datasets, such as the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and CAMS global atmospheric composition forecasts (CAMS-F). We found that the default setting of FLEXDUST substantially underestimates the strength of dust emission and FLEXPART modelled dust concentration in this storm compared to that in MERRA-2 and CAMS-F. An improvement of the parametrization of bare soil fraction, topographical scaling, threshold friction velocity and vertical dust flux scheme based on Kok et al. (Atmospheric Chemistry and Physics, 2014, 14, 13023-13041) in FLEXDUST can reproduce the strength and spatio-temporal pattern of the dust storm comparable to MERRA-2 and CAMS-F. However, it still underestimates the observed spike of dust concentration during the dust storm event over northern China, and requires further improvement in the future. The improved FLEXDUST and FLEXPART perform better than MERRA-2 and CAMS-F in capturing the observed particle size distribution of dust aerosols, highlighting the importance of using more dust size bins and size-dependent parameterization for dust emission, and dry and wet deposition schemes for modelling the Asian dust cycle and its climatic feedbacks.Peer reviewe

Aeolian dust sources, transport and deposition over the Chinese Loess Plateau during 1999-2019: A study using the FLEXDUST and FLEXPART models

The aeolian dust deposits over the Chinese Loess Plateau (CLP) contain valuable information about past environmental changes in Asia. Unlocking this information requires understanding the East Asian dust cycle (EADC) and, particularly, the components of the EADC regarding the emissions, transport and deposition of aeolian dust over the CLP. In this work, the dust emission model FLEXDUST and the FLEXible PARTicle Dispersion Model (FLEXPART) were employed to study the dust cycle over the CLP (referred to as the EADC) from 1999 until 2019, during the dust event season March until May. Backward dust transport trajectories were calculated using FLEXPART from seven sites across the CLP. Two particle size bins 1.7μm-2.5μm representing clay particles and 15μm-20μm representing silt particles were included to examine the influence of particle size on dust transport and deposition, with wet and dry deposition being simulated, respectively. The trajectory information from FLEXPART is combined with the dust emission field from FLEXDUST to produce a high-resolution map of the source contribution for each deposition site. The FLEXPART/FLEXDUST modelling setup was found to reasonably represent the EADC compared to observations, especially its spatial and temporal variations. The main source of the dust deposited to CLP is the deserts to the northwest of the CLP. Wet deposition is the major contributor to the deposition of dust particles over the CLP, especially for the coarse silt particles through high-level tropospheric transport. An extensive correlation analysis between spring dust emissions, deposition and several climate indices reveals a strong correlation of dust deposition over the CLP with the winter AO, but not with the EAWM. This contrasts with previous studies presuming a strong control of the EAWM on the dust deposition over the CLP. Our results show that strong dust deposition years were characterised by a negative AO and an anomaly in the winter 500hPa geopotential height over Mongolia/Siberia. The location of the geopotential height anomaly was consistent with previous studies on the cold air outbreak (CAOB) paths, indicating a key role of AO in regulating the frequency, intensity and path of CAOB intruding into East Asia, which primarily causes dust events in East Asia