Reddy: An open-source toolbox for analyzing eddy-covariance measurements in heterogeneous environments

Abstract: Land-atmosphere exchange processes are determined by turbulent fluxes, which can be derived from eddy-covariance measurements. This method was established to quantify ecosystem-scale vertical atmosphere-vegetation exchange processes, but is also used to validate atmospheric turbulence theories with the ultimate aim to improve the representation of turbulence in numerical models. While the focus has long been on turbulence over idealized, homogeneous and flat surfaces, recent scientific developments are shifting towards investigating turbulent exchange processes in complex heterogeneous environments under non-idealized conditions, which pose particular challenges, e.g. advective fluxes between different surface types or non-stationarity of nighttime turbulence. This requires to rethink standard post-processing routines for determining turbulent fluxes from the high-frequency sonic and gas analyzer measurements. Here, we introduce the open-source R-package 'Reddy', which provides modular-built functions for post-processing, analysis and visualization of eddy-covariance measurements, including investigating spectra, coherent structures, anisotropy, flux footprints and surface energy balance closure. The 'Reddy' package is accompanied by a detailed documentation and a set of jupyter notebooks introducing new users hands-on to eddy-covariance data analysis. We showcase 'Reddy' based on measurements from three different sites in Norway: A case study during strong stratification over alpine tundra, for determining suitable averaging times during ice-cover transition at a boreal lake, and for fitting flux-variance relations for a permafrost peatland. 'Reddy' serves as extension of previously developed software packages, paving the way towards holistic turbulence data analysis in heterogeneous real-world environments.