CloudRoots: Integration of advanced instrumental techniques and process modelling of sub-hourly and sub-kilometre land-atmosphere interactions

Abstract

<jats:p>Abstract. The CloudRoots field experiment was designed to obtain a comprehensive observational data set that includes soil, plant and atmospheric variables to investigate the interaction between a heterogeneous land surface and its overlying atmospheric boundary layer at the sub-hourly and sub–kilometre scale. Our findings demonstrate the need to include measurements at leaf level in order to obtain accurate parameters for the mechanistic representation of photosynthesis and stomatal aperture. Once the new parameters are implemented, the mechanistic model reproduces satisfactorily the stomatal leaf conductance and the leaf-level photosynthesis. At the canopy scale, we find a consistent diurnal pattern on the contributions of plant transpiration and soil evaporation using different measurement techniques. From the high frequency and vertical resolution state variables and CO2 measurements, we infer a profile of the plant assimilation that shows a strong non-linear behaviour. Observations taken by a laser scintillometer allow us to quantify the non-steadiness of the surface turbulent fluxes during the rapid changes driven by perturbation of the photosynthetically active radiation (PAR) by clouds, the so-called cloud flecks. More specifically, we find two-minute delays between the cloud radiation perturbation and ET. The impact of surface heterogeneity was further studied using ET estimates infer from the sun-induced fluorescence data and show small variation of ET in spite of the plant functional type differences. To study the relevance of advection and surface heterogeneity on the land-atmosphere interaction, we employ a coupled surface-atmospheric conceptual model that integrates the surface and upper-air observations taken at different scales: from the leaf-level to the landscape. At the landscape scale, we obtain the representative sensible heat flux that is consistent with the evolution of the boundary-layer depth evolution. Finally, throughout the entire growing season, the wide variations in stomatal opening and photosynthesis lead to large variations of plant transpiration at the leaf and canopy scales. The use of different instrumental techniques enables us to compare the total ET at various growing stages, from booting to senescence. There is satisfactory agreement between evapotranspiration of total ET, but the values remain sensitive to the scale at which ET is measured or modelled. </jats:p>

Comment on gmd-2020-371

“…The results of the present work indicate that the tabulated values, which were developed for other region/dates or even with a different type of conifer or density of trees, should be revised. This is consistent with the scientific demand for systematic experimental observations representative of different scales (Vilà-Guerau de Arellano et al, 2020), from the leaf-level (as stomatal conductance) to the landscape and model grid-scales (for example reliable area-averaged fluxes).…”

Evapotranspiration over Land from a Boundary-Layer Meteorology Perspective

“…They are more difficult to apply for natural vegetation, since it is usually a mixture of several plant species. A recent attempt to combine these methods with standard micrometeorological measurements is the CloudRoots field experiment (Vilà-Guerau de Arellano et al, 2020), that shows that information at the leaf level is necessary to obtain accurate parameters for the mechanistic representation of photosynthesis and stomatal aperture, and that sun-induced fluorescence data can be used to estimate the spatial variability of ET.…”

Investigating the Diurnal Radiative, Turbulent, and Biophysical Processes in the Amazonian Canopy‐Atmosphere Interface by Combining LES Simulations and Observations

“…Possible causes for the misrepresentation are of soil and ecophysiological origin: an underestimation of soil respiration or the overestimation of CO 2 uptake at leaf level. These issues reinforce the need to have detailed measurements for the photosynthesis dependance on PAR and on the carbon gradient between the leaf and surrounding air at short spatiotemporal scales (Vilà‐Guerau de Arellano, Ney, et al., 2020). The BULK simulation shows larger discrepancies, falling outside the standard deviation, with the observed fluxes in Figures 8a–8c.…”

“…Long term co‐located measurements of all these processes would be the end goal, while intensive and short campaigns would already be of use for the modeling community. As coupled models advance in the explicit solving of those processes, the availability of data sets with high‐spatiotemporal resolution against which numerical experiments can be validated in terms of, for example, upwards and downwards radiation, leaf temperatures or stomatal conductance, is indispensable (Helbig et al., 2021; Vilà‐Guerau de Arellano, Ney, et al., 2020). In the case of leaf measurements such as leaf‐level fluxes, leaf temperature and stomatal conductance, there is plenty of data on laboratory conditions.…”