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Illuminating the dark side of surface meteorology: creating a novel framework to explain atmospheric transport and turbulent mixing in the weak-wind boundary layer

Periodic Reporting for period 3 - DarkMix (Illuminating the dark side of surface meteorology: creating a novel framework to explain atmospheric transport and turbulent mixing in the weak-wind boundary layer)

Reporting period: 2020-05-01 to 2021-10-31

Surface meteorology impacts the abundance and quality of life on Earth through the transfer and mixing of light, heat, water, carbon dioxide, and other substances controlling the resources for humans, plants, and animals. However, current theories and models fail when airflows and turbulence are weak during calm cloudless nights leaving weather, climate, and air quality forecasts uncertain. This ‘dark side’ has also escaped proper experimental investigation because of insufficient representation of the naturally occurring large variability in atmospheric transport and mixing. DarkMix aims at causing a quantum leap in our understanding of air quality issues and the biogeochemical cycling of carbon, water and heat by giving physically meaningful and societally relevant answers to profound questions such as the exchange of greenhouse gases, hazards from ground fog, urban pollution, and agricultural losses through frost damage. The main objective is to combine the technological innovation of the first ever fiber-optics-based high-resolution environmental sensor for temperature and wind with an innovative theory to create a radically novel framework to answer the above-mentioned standing environmental issues.
To date, we have achieved the major part of the technical innovation by developing and demonstrating the exceptional performance of the innovative fiber-optic environmental sensor now capable of also observing wind direction both in laboratory and field settings. We named this new technique Large Eddy Observation (LEO). Distributed observations of wind direction enable computing the direction of the transport and strength of atmospheric mixing. Along this path, we have developed new technologies for enhanced sensor signal calibration and data processing. We disseminated our research achievements to the Earth sciences community including meteorologists, hydrologists, geologists, and biologists by leading the first openly announced interdisciplinary workshop on fiber-optic technology in Europe. The LEO sensor was used to conduct the first large field campaign on an agricultural field in the bottom of a mid-range mountain valley investigating cold airflows, cold-air pools, and frost formation even in summer conditions.
Development of the LEO technique and demonstrating its utility to visualize and quantify airflows in unprecedented detailedness and spatial coverage was a major breakthrough in observational surface meteorology. We will continue to refine the LEO technique and anticipate resolving the remaining technical challenges until the end of the DarkMix funding period. Ongoing analysis and interpretation of the LEO data from the first successfully completed and two forthcoming field campaigns in forest and urban settings will lead to achieving the theoretical innovation by incorporating poorly understood atmospheric mechanisms characteristic for weak winds during calm cloudless nights. Now that LEO is available, its observations will be used to inform and validate simulations of airflows from the well-established Large Eddy Simulation (LES) technique. In DarkMix, LES will be used as a virtual laboratory for hypothesis testing and aiding in formulating the theoretical innovation. Until completion of DarkMix, we expect to formulate a firm understanding when and where cold-air pools often combined with frost and ground fog develop, to have improved estimates of the carbon forest sink, and to better forecast air quality and hazards in cities.
DarkMix technical innovation: the first field-scale LEO element
DarkMix technical innovation:LEO microscopic approach to sensing wind direction with coned fibers
DarkMix Field campaign in agricultural setting: morning cold-air pool and ground fog formation
DarkMix: deploying fiber-optic cables for vertical profiling on tethered balloons (FLYFOX)