Abstract
AbstractThe explicit coupling at meter and second scales of vegetation's responses to the atmospheric‐boundary layer dynamics drives a dynamic heterogeneity that influences canopy‐top fluxes and cloud formation. Focusing on a representative day during the Amazonian dry season, we investigate the diurnal cycle of energy, moisture and carbon dioxide at the canopy top, and the transition from clear to cloudy conditions. To this end, we compare results from a large‐eddy simulation technique, a high‐resolution global weather model, and a complete observational data set collected during the GoAmazon14/15 campaign. The overall model‐observation comparisons of radiation and canopy‐top fluxes, turbulence, and cloud dynamics are very satisfactory, with all the modeled variables lying within the standard deviation of the monthly aggregated observations. Our analysis indicates that the timing of the change in the daylight carbon exchange, from a sink to a source, remains uncertain and is probably related to the stomata closure caused by the increase in vapor pressure deficit during the afternoon. We demonstrate quantitatively that heat and moisture transport from the subcloud layer into the cloud layer are misrepresented by the global model, yielding low values of specific humidity and thermal instability above the cloud base. Finally, the numerical simulations and observational data are adequate settings for benchmarking more comprehensive studies of plant responses, microphysics, and radiation.
Highlights
Two of the most important uncertainties in climate studies are associated with the impact of clouds on radiative transfer (Schneider et al, 2017; Zelinka et al, 2017) and the terrestrial carbon dioxide (CO2) sink (Le Quéré et al, 2009)
Motivated by the interaction between the Amazonian tropical forest and the dynamic spatial patterns formed by clouds, the green-white ocean-atmosphere system, we used our canopy-top and upper-atmospheric observations to evaluate systematically the numerical shallow cumuli experiments interactively coupled to vegetation
This study focuses on the final period of the dry season, in September 2014, which is crucial to the onset of the Amazonian tropical forest wet season
Summary
Two of the most important uncertainties in climate studies are associated with the impact of clouds on radiative transfer (Schneider et al, 2017; Zelinka et al, 2017) and the terrestrial carbon dioxide (CO2) sink (Le Quéré et al, 2009) These uncertainties are typically quantified by global circulation models (Vial et al, 2013). Photosynthesis and stomatal aperture responses to radiative perturbations influence (i) the surface energy balance (Doutriaux-Boucher et al, 2009; Pedruzo-Bagazgoitia et al, 2017; Sikma et al, 2018), (ii) key length scales of clouds such as their horizontal size and cloud separation (Horn et al, 2015), and (iii) cloud transport properties (Sikma & Vilà-Guerau de Arellano, 2019) In reproducing these couplings, the model's representation of the radiative transfer at the canopy top perturbed by clouds plays a key role (Jakub & Mayer, 2017)
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