Life Cycle of Stratocumulus Clouds over one Year at the Coast of the Atacama Desert

Abstract. Marine stratocumulus clouds of the Eastern Pacific play an essential role in the Earth's energy and radiation budget. Parts of these clouds off the west coast of South America form the major source of water to the hyper-arid Atacama Desert coastal region at the northern coast of Chile. For the first time, a full year of vertical structure observations of the coastal stratocumulus and their environment are presented and analysed. Installed at Iquique Airport in northern Chile in 2018/2019, three state-of-the-art remote sensing instruments provide vertical profiles of cloud macro- and micro-physical properties, wind, turbulence and temperature, as well as integrated values of water vapor and liquid water. Distinct diurnal and seasonal patterns of the stratocumulus life-cycle are observed. Embedded in a land-sea circulation with a super-imposed southerly wind component, maximum cloud occurrence and vertical extent occurs at night, whereas minima during local noon. Night-time clouds are maintained by cloud-top cooling, whereas afternoon clouds re-appear within a convective boundary layer driven through local moisture advection from the Pacific. During the night, these clouds finally re-connect to the maritime clouds in the upper branch of the land-sea circulation. The diurnal cycle is much more pronounced in austral winter with lower, thicker and more abundant (5x) clouds than in summer. This can be associated to different SST gradients in summer and winter, leading to a stable, respectively neutral stratification of the maritime boundary layer at the coast of the Atacama Desert in Iquique.