This study investigates the atmospheric dynamics of the major dust storm that occurred in June 2020 over the Sahara and during which dust clouds associated with the highest-on-record aerosol optical depths were transported towards the America. An anomalous atmospheric circulation pattern in the mid-latitudes, linked to a circum-global wavetrain, resulted in the development of a subtropical high-pressure system to the west of the Saharan Heat Low. This created a pressure dipole and generated anomalously strong northeasterlies over the Sahara, which caused continuous dust emissions over 4 days. Occurring along the northern fringes of the Intertropical Discontinuity, the dust was transported to higher altitudes (6 km) by the strong updraft in this region. This injected the dust at the African Easterly Jet (AEJ) altitudes and favored a rapid westward long-range transport. The AEJ was also anomalously strong, being strengthened by the anticyclonic circulation associated with the anomalous high. Plain Language Summary Dust is an important constituent of the Earth's atmosphere, with a wide range of impacts ranging from human health to effects on climate. In June 2020, massive amounts of dust were lifted from the Sahara, the major dust source region in the world, and transported all the way into the Americas across the tropical Atlantic Ocean. This event was caused by the development of a subtropical high-pressure system over northwest Africa which resulted in sustained strong northeasterlies over the Sahara generating continuous dust emissions for 4 days. Due to the strong low-level convergence along the intertropical discontinuity region, the dust was lifted to roughly 5-6 km above the surface, and then transported westward by the stronger mid-atmospheric winds (>20 m s-1). At Cape Verde and over large swaths of the Atlantic Ocean, the amount of dust suspended in the atmosphere was associated with the largest aerosol optical depths on record.

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Abstract. Cloud vertical structure, including top and base altitudes, thickness of cloud layers, and the vertical distribution of multilayer clouds, affects large-scale atmosphere circulation by altering gradients in the total diabatic heating and cooling and latent heat release. In this study, longterm (11 years) observations of high-vertical-resolution radiosondes are used to obtain the cloud vertical structure over a tropical station at Gadanki (13.5 • N, 79.2 • E), India. The detected cloud layers are verified with independent observations using cloud particle sensor (CPS) sonde launched from the same station. High-level clouds account for 69.05 %, 58.49 %, 55.5 %, and 58.6 % of all clouds during the premonsoon, monsoon, post-monsoon, and winter seasons, respectively. The average cloud base (cloud top) altitudes for low-level, middle-level, high-level, and deep convective clouds are 1.74 km (3.16 km), 3.59 km (5.55 km), 8.79 km (10.49 km), and 1.22 km (11.45 km), respectively. Singlelayer, two-layer, and three-layer clouds account for 40.80 %, 30.71 %, and 19.68 % of all cloud configurations, respectively. Multilayer clouds occurred more frequently during the monsoon with 34.58 %. Maximum cloud top altitude and cloud thickness occurred during the monsoon season for single-layer clouds and the uppermost layer of multiple-layer cloud configurations. In multilayer cloud configurations, diurnal variations in the thickness of upper-layer clouds are larger than those of lower-layer clouds. Heating and cooling in the troposphere and lower stratosphere due to these cloud layers are also investigated and peak cooling (peak warming) is found below (above) the cold-point tropopause (CPT) altitude. The magnitude of cooling (warming) increases from single-layer to four-or more-layer cloud occurrence. Further, the vertical structure of clouds is also studied with respect to the arrival date of the Indian summer monsoon over Gadanki.

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