Comment on egusphere-2022-18

Abstract

Drought is an extreme hydroclimate event that has been shown to cause the increase of surface fine dust near source regions, while the drought-dust relationship in regions predominantly influenced by long-range transported dust such as the southeastern US (SEUS) has received less attention. Using long-term surface fine dust observations, weekly US Drought Monitor (USDM), and monthly Standardized Precipitation-Evapotranspiration Index (SPEI), this study unmasks spatial disparity in drought-dust relationships where the SEUS stands out as being abnormous in that it shows a decrease in surface dust concentrations during drought in contrast to the expected increase in dust found in other contiguous US (CONUS) regions. Surface fine dust was found to decrease by ~0.5 µg/m3 with a unit decrease of SPEI in the SEUS, as opposed to an increase of ~0.15 µg/m3 in the west. The anomalies of elemental ratios, satellite aerosol optical depth (AOD), and dust extinction coefficients suggest that both the emissions and trans-Atlantic transport of African dust are weakened when the SEUS is under droughts. Through the teleconnection patterns of negative North Atlantic Oscillation (NAO), a lower than normal and more northeastward displacement of the Bermuda High (BH) was present during SEUS droughts which resulted in less dust being transported into the SEUS. At the same time, enhanced precipitation in Sahel associated with the northward shift of the Intertropical Convergence Zone (ITCZ) leads to lower dust emissions therein. Of the four selected models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6), GISS-E2-1-G was found to perform the best in capturing the drought-dust sensitivity in the SEUS. This study reveals the mechanism of how regional-scale droughts influence aerosol abundance through changing long-range transport of dust.