A Climatology of Dust Activity in the Atacama for 1950-2021

Arid and semi-arid regions are sources of mineral-dust aerosols but very little is known of the dust activity in the hyper-arid Atacama Desert. The limited moisture supply and barren landscape should promote dust emission via wind erosion but the Atacama rarely sees strong dust outbreaks. Our study is the first detailed assessment of the observed dust reports for the Atacama. We analysed dust reports and meteorological data from surface synoptic observations spanning 72 years (1950-2021) to quantify the frequency distribution of dust events in the Atacama Desert, analyze changes over time, and evaluate influencing factors on dust events. Furthermore, we computed the threshold wind speeds for dust events at the different stations. A total of 1920 dusty days were recorded over a period of 72 years across the Atacama, where a dusty day is defined as a day with at least one recorded dust event. There is no perceptible trend visible but the results indicate several year-long periods with enhanced dust activity. Most dust events were observed in the 1990s with a rapid decline in dust activity post the early 2000s. Of the 1920 dust days, 72 days had a visibility of less than a kilometre, of which 12 days also reported dust storms. Chañaral was the dustiest station in the region with about 20 dust days per year. There is little seasonality in the dust activity, but a strong diurnal cycle with most dust events between 1500 and 1800 local time. Threshold wind speeds, t5, t25 and t50, are estimated as the minimum wind speed required for 5, 25 and 50% of the dust event frequency distribution. The thresholds allow us to determine the lowest winds capable of emitting dust from the surface and infer spatial differences in soil conditions due to soil moisture or land cover. Given the varying geomorphology of the surfaces in the Atacama, different threshold wind speeds are found at the stations in the Atacama. The t5 threshold wind speeds range from 6 ms^-1to 14 ms^-1across the desert. The evaluation of all stations yields annual mean threshold wind speeds of 10.9 ±1.6 ms^-1, 13.2 ±1.9 ms^-1and 15.6 ±2.3 ms^-1for t5, t25 and t50. Ongoing research aims to evaluate the findings for the threshold wind speed against measurements from the pi-swerL Atacama Measurement EXperiment (LAMEX) conducted in October 2022.