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. DarkMix aims at a quantum leap in our understanding of atmospheric transport in weak-wind condition relevant for urban air quality, biogeochemical cycling of greenhouse gases in forests, and agricultural frost damage. The main objective is to combine the technological innovation of the first fiber-optics-based high-resolution environmental sensor for temperature and wind with an innovative theory of a novel conceptual framework to answer the above-mentioned environmental processes.
At completion of the project, we conclude that the project was successful in achieving the technological innovation of constructing and validating the first-ever field-scale fiber-optic distributed sensing system able to resolve the spatial structure of fast-lived turbulent atmospheric motions. We name the novel observational technique 'Large Eddy Observation'. LEO is capable of measuring the fast-changing direction of the airflow as well as the heat transported by the air current without any ancillary measurements from classical atmospheric sensors in certain environments. From the results we gained from deploying LEO in combination with classic sensor networks above grasslands in valley bottoms, forests, and an urban area we conclude that the atmospheric motions generating transport and mixing are different across land covers while all occur in weak winds. Motions above the agricultural grassland in the valley favor horizontal transport and longer-lived wind directional changes, while vertical scales are suppressed by the strong vertical temperature differences. In contrast, in forests and urban environments the weak-wind motions are more three dimensional since the vertical temperature differences are weaker and the airflow interacting with trees and built structures creates additional mixing. Despite their differences, we conclude that results start to converge into the theoretical innovation of the new framework. While its construction continues, we formulated a novel universally applicable quantity, which explains vertical mixing and decoupling irrespective of the environment. We have successfully used it to separate mixing regimes in conditions of the Arctic polar night over snow, agricultural lands in mid-latitude, boreal and temperate forests, as well a mid-European city. While the theoretical innovation is not complete yet, we will continue our research in this promising direction.
