The controlling factors regulating moisture supply across the CRC1211 study areas are dominated by water vapor and fog, although seldom (extreme) precipitation events can significantly influence landscapes and life in the Atacama Desert. In the first phase of the CRC, a ground-based remote sensing supersite was installed which, together with the CRC’s meteorological station network, builds a unique data base for gaining process understanding and to anchor modelling and satellite efforts. In the second funding period high resolution modelling, using an unprecedented resolution (~600 m) and realistic forcing conditions, was established as a tool to better understand the governing processes at the local scale. To provide knowledge on Atacama-wide fog and low cloud occurrence for various CRC projects, novel machine learning algorithms for satellite data exploiting station data were developed and applied. Satellite and reanalysis data gave new insights into the large-scale transport of moisture including its importance for extreme precipitation. Comparisons between the Atacama and Namib deserts identified distinct differences in the seasonal behavior of the moisture supply pointing at reasons for the more hyper-arid conditions within the Atacama Desert.

During phase 3 of the CRC, we will build upon the established observational and modelling infrastructure as well as on the obtained understanding about the processes governing moisture supply to the Atacama and Namib deserts. The synthesis of our findings now makes it possible to quantify the different moisture sources and their spatial-temporal variability for the Atacama Desert and investigate the dependence on large-scale forcing factors. While our efforts are mainly geared towards the recent climate for which excellent data are available, we will also reach out to project the results to the paleoclimate and information gained from other CRC projects during Phase 1 and 2. Particular interest is in quantifying fog water deposition as an important input for biological and pedogenic processes for which we plan to transfer the obtained detailed knowledge on the local scale to develop parameterizations for the broader scale. Three main research questions will be addressed in phase 3:

1. Can we – by using a synergy of satellite, ground-based in-situ and high-resolution modelling – quantify typical horizontal and vertical fog-water fluxes into Atacama Desert?
2. How does the fog-water input vary in time and space and how does this relate to time-of-day, weather situation, season, ENSO mode?
3. How do the horizontal and vertical (fog)-water fluxes in the recent climate differ compared to the warmer climate of the Mid-Pliocene?

Modern and past climate: Investigation of atmospheric water supply to the Atacama Desert and comparative studies with the Namib Desert

Research areas: Atmospheric Science and Oceanography

Principal investigators: Prof. Dr. Susanne Crewell, Dr. Ulrich Löhnert

Overall research theme: "On which paths does water reach the Atacama and Namib Deserts?"

The controlling factors regulating moisture supply across the CRC study area in Chile are dominated by the transport of water vapor and the formation of fog. Here, we plan to characterize related multi‐scale circulation features and quantify their impact on the Atacama Desert moisture supply. Land‐sea circulation patterns from the Pacific over the coastal cliff, the Costal Cordillera, the Central Depression, towards the Andes and back will be identified from east‐west meteorological station transects (available in the CRC since 2017), the remote sensing station at Iquique airport (deployment 2018/2019), high‐altitude astronomy‐driven measurements of temperature and water vapor and the high‐resolution GOES16 satellite in a synergistic manner. The high‐resolution (~100 m) ICON Large Eddy Model (LEM) will be used in a multiple‐nest‐framework to fill the observational gap in order to constrain the distribution of water within the Atacama Desert. Furthermore, we aim to identify robust characteristics of the large‐scale circulation during the present climate as a proxy for moisture supply which can serve the interpretation of palaeo records (A02, A04). For this, we will continue to exploit the longest reanalysis available, e.g. the 110‐year record of ERA‐20C, for both the Atacama and the Namib study area and investigate climate variability of the water cycle, e.g. associated to large‐scale climate modes. Satellite measurements which are not assimilated into ERA‐20C are now available since several decades and will thus allow linking the local to the larger scale. Based on these comprehensive satellite data records and reanalysis, a comparative assessment of the water cycle in the Atacama and the Namib Deserts will be performed.

Modern and past climate: Investigation of atmospheric water supply to the Atacama desert (Chile) from combined in-situ, ground-based and satellite remote sensing observations

Research areas: Atmospheric Science and Oceanography

The extremely dry regions of northern Chile pose a challenging environment for vegetation and fauna in respect to moisture supply. The meteorological situation is complex due to ocean-atmosphere-land coupling under the strong influence of orography and (anthropogenic) aerosol.

Few operational measurements are performed in the region and the rare satellite studies have been limited by resolution aspects due to the structured relief. We aim to characterise present day climate based on a combination of in-situ meteorological stations to be deployed along three transects, various satellite observations as well as ground-based remote sensing observations. The long-term objective is to link the local availability of atmospheric water (i.e. water vapour and fog) to larger scale proxies (i.e. synoptic weather pattern, multi-decadal forcing) in order to establish downscaling rules for past and future climate. For an enhanced process understanding we will carry out a measurement campaign employing (amongst others) a novel type of highly sensitive cloud radar at the fog research site Alto Patache and analyse in-situ measurements by meteorological stations operated at locations not assessed before. By combination with long-term satellite and atmospheric reanalysis data, an unprecedented characterization of the local and large-scale processes leading to low-cloud and fog occurring over the transition region between Eastern Pacific and the Chilean high altitude desert region will be possible. Atmospheric reanalysis and long-term satellite data stream will also enable to describe the spatiotemporal availability of water vapour for different types of climatic variability, such as the Pacific Decadal Oscillation.

Former members:

• Prof. Dr. Susanne Crewell (Principal Investigator)
• Dr. Ulrich Löhnert (Principal Investigator)

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