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Essential Ecosystem Variables
Abstract:
Interactions between the biosphere and the atmosphere can be well characterized by fluxes between
the two. In particular, carbon and energy fluxes play a major role in understanding biogeochemical processes on
an ecosystem level or global scale. However, the fluxes can only be measured at individual sites, e.g., by eddy
covariance towers, and an upscaling of these local observations is required to analyze global patterns. Previous
work focused on upscaling monthly, 8-day, or daily average values, and global maps for each flux have been provided
accordingly. In this paper, we raise the upscaling of carbon and energy fluxes between land and atmosphere
to the next level by increasing the temporal resolution to subdaily timescales.We provide continuous half-hourly
fluxes for the period from 2001 to 2014 at 0:5 spatial resolution, which allows for analyzing diurnal cycles
globally. The data set contains four fluxes: gross primary production (GPP), net ecosystem exchange (NEE),
latent heat (LE), and sensible heat (H). We propose two prediction approaches for the diurnal cycles based on
large-scale regression models and compare them in extensive cross-validation experiments using different sets
of predictor variables. We analyze the results for a set of FLUXNET tower sites showing the suitability of our
approaches for this upscaling task. Finally, we have selected one approach to calculate the global half-hourly
data products based on predictor variables from remote sensing and meteorology at daily resolution as well as
half-hourly potential radiation. In addition, we provide a derived product that only contains monthly average
diurnal cycles, which is a lightweight version in terms of data storage that still allows studying the important
characteristics of diurnal patterns globally. We recommend to primarily use these monthly average diurnal cycles,
because they are less affected by the impacts of day-to-day variation, observation noise, and short-term
fluctuations on subdaily timescales compared to the full half-hourly flux products. The global half-hourly data
products are available at https://doi.org/10.17871/BACI.224.
