The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

[1] Measurements of the energy balance components of a small boreal lake (area 0.041 km 2 , mean depth 2.5 m) in southern Finland were performed during four open water periods (April-October) in [2005][2006][2007][2008]. Turbulent fluxes of sensible and latent heat acquired using the eddy covariance technique were accompanied by net radiation and water heat storage measurements. In April the lake was near isothermal, whereas in May the development of a thermocline was enabled by dark water color and a sheltered location. The thermocline continued to deepen until September down to the depth of 3.5 m and prevented the deeper water from interacting with the atmosphere. The sensible heat flux was governed by the air-water temperature difference and had its minimum in the afternoon (values down to −45 W m Citation: Nordbo, A., S. Launiainen, I. Mammarella, M. Leppäranta, J. Huotari, A. Ojala, and T. Vesala (2011), Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique,

In this study the high-frequency loss of carbon dioxide (CO 2 ) and water vapor (H 2 O) fluxes, measured by a closed-path eddy covariance system, were studied, and the related correction factors through the cospectral transfer function method were calculated. As already reported by other studies, it was found that the age of the sampling tube is a relevant factor to consider when estimating the spectral correction of water vapor fluxes. Moreover, a time-dependent relationship between the characteristic time constant (or response time) for water vapor and the ambient relative humidity was disclosed. Such dependence is negligible when the sampling tube is new, but it becomes important already when the tube is only 1 yr old and increases with the age of the tube. With a new sampling tube, the correction of water vapor flux measurements over a Scots pine forest in Hyytiä lä , Finland, amounted on average to 7%. After 4 yr the correction increased strongly, ranging from 10%-15% during the summer to 30%-40% in wintertime, when the relative humidity is typically high. For this site the effective correction improved the long-term energy and water balance.Results suggest that the relative humidity effect on high-frequency loss of water vapor flux should be taken into account and that the effective transfer function should be estimated experimentally at least once per year. On the other hand, this high correction can be avoided by a correct choice and periodic maintenance of the eddy covariance system tube, for example, by cleaning or changing it at least once per year.

[1] Long-term measurements of sensible and latent heat and carbon dioxide fluxes were performed over a boreal lake in southern Finland using the direct micrometeorological eddy covariance (EC) technique. The water column was sampled weekly for dissolved carbon dioxide, and the CO 2 flux was estimated also applying the concentration gradient method. Temperature and oxygen profiles of the lake were measured twice a week. The measurements covered one full open-water period from April to November 2003, and it is the longest continuous CO 2 record ever measured over a lake by EC. The sensible heat flux H was positive, that is, from the lake to the atmosphere, except in May, when it was >0 W/m 2 at night and <0 W/m 2 in daytime. The latent heat flux dominated clearly over H in spring and summer; that is, the Bowen ratio was less than 1. Highermoment turbulence statistics proved to be efficient in detection of frequent nonstationary situations. Applying the statistical criteria for CO 2 concentration and vertical wind speed, averaging over a 5-min period and selecting only the wind direction with longest fetch, we could obtain lake-representative CO 2 fluxes. Footprint analysis based on a closure model revealed that the source areas were relatively short because of the presence of turbulence generated by the surrounding forest, compared to a larger lake with an extended smooth surface. We observed a net CO 2 source of 0.2-0.4 mmol m À2 s À1 excluding July, when the flux was closer to zero. The results are consistent with the gradient method, based on more infrequent sampling, and both methods gave the same average flux, 0.2 mmol m À2 s À1 , over the whole open-water period.