Publications by authors named "Ullar Rannik"

Article Synopsis
  • - The FLUXNET2015 dataset encompasses ecosystem-scale data on carbon dioxide, water, and energy exchange, collected from 212 global sites contributing over 1500 site-years of data until 2014.
  • - The dataset was systematically quality controlled and processed, facilitating consistency for various applications in ecophysiology, remote sensing, and ecosystem modeling.
  • - For the first time, derived data products such as time series, ecosystem respiration, and photosynthesis estimates are included, and 206 sites are made accessible under a Creative Commons license, with the processing methods available as open-source codes.
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Nitrous oxide (N2O) is an important greenhouse gas produced in soil and aquatic ecosystems. Its warming potential is 296 times higher than that of CO2. Most N2O emission measurements made so far are limited in temporal and spatial resolution causing uncertainties in the global N2O budget.

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In species that disperse by airborne propagules an inverse relationship is often assumed between propagule size and dispersal distance. However, for microscopic spores the evidence for the relationship remains ambiguous. Lagrangian stochastic dispersion models that have been successful in predicting seed dispersal appear to predict similar dispersal for all spore sizes up to -40 microm diameter.

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In contrast with recent advances on the dynamics of the flow at a forest edge, few studies have considered its role on scalar transport and, in particular, on CO2 transfer. The present study addresses the influence of the abrupt roughness change on forest atmosphere CO2 exchange and contrasts the concentration and flux fields against those of a uniform forested surface. We use an atmospheric boundary layer two-equation closure model that accounts for the flow dynamics and vertical divergence of CO2 sources/sinks within a plant canopy.

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We simulated the REA system with dynamic deadband to study numerical value and the effect of atmospheric conditions on the empirical constant beta which relates vertical flux to concentration difference between updrafts and downdrafts. We found that the value of beta depends only weakly on the friction velocity and atmospheric stability. In agreement with previous studies, the median value obtained for a system with dynamic deadband proportional to 0.

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