Quantifying the transport of subcloud layer reactants by shallow cumulus clouds over the Amazon

Abstract

[1] We investigate the vertical transport of atmospheric chemical reactants from the subcloud layer to the cumulus cloud layer driven by shallow convection over the Amazon during the dry season. The dynamical and chemical assumptions needed for mesoscale and global chemistry transport model parametrizations are systematically analyzed using a Large Eddy Simulation model. We quantify the mass flux transport contribution to the temporal evolution of reactants. Isoprene, a key atmospheric compound over the tropical rain forest, decreases by 8.5% h -1 on average and 15% h -1 at maximum due to mass-flux-induced removal. We apply mass flux parametrizations for the transport of chemical reactants and obtain satisfactory agreement with numerically resolved transport, except for some reactants like O 3 , NO, and NO 2 . The latter is caused by the local partitioning of reactants, influenced by UV radiation extinction by clouds and small-scale variability of ambient atmospheric compounds. By considering the longer-lived NO x (NO + NO 2 ), the transport is well represented by the parametrization. Finally, by considering heterogeneous surface exchange conditions, it is demonstrated that the parametrizations are sensitive to boundary conditions due to changes in the boundary layer dynamics.

Cloud Shading Effects on Characteristic Boundary-Layer Length Scales

“…The initial atmospheric conditions used are based on the TROpical Forest and Fire Emissions Experiment (TROFFEE) (Karl et al 2007;Vilà-Guerau de Arellano et al 2011), adapted by Ouwersloot et al (2013) to ensure that shallow Cu convection occurs with no deep convection. The initial conditions follow Amazonian surface and upper-air conditions: the initial boundary-layer height is 200 m with a potential temperature (θ ) of 300 K and a specific humidity (q) of 16 × 10 −6 kg kg −1 .…”

Large Eddy Simulation of the Interaction Between Biogenic Volatile Organic Compound Transport and Chemistry Within a Tropical Forest Canopy

“…Chemical species are included in the LES as reactive tracers. Isoprene oxidation processes related to ozone, the nitrate and hydroxyl radicals are included by using the atmospheric chemistry module from the Dutch Atmospheric LES (DALES) (Ouwersloot et al, 2013).…”

“…MC and JDF acknowledge partial funding from DOE through the Office of Biological and Environmental Research (BER) Atmospheric Ouwersloot, H.G., de Arellano, J.V., H. van Stratum, B.J., Krol, M.C., Lelieveld, J., (2013 Kruijt, B., Malhi, Y., Lloyd, J., Norbre, A.D., Miranda, A.C., Pereira, M.G.P., Culf, A., Grace, J., (2000). Turbulence statistics above and within two Amazon rain forest canopies.…”

On the interactions between clouds, radiation, turbulence and vegetation in the atmospheric boundary layer

“…Since we are also interested in the properties of the clouds during the experiment, we make further use of a three-dimensional conditional average over the grid, similar to that used in other studies Ouwersloot et al, 2013;Sikma and Ouwersloot, 2015). In this case, we mainly focus on the conditional averages for clouds (q l > 0) and for the buoyant part of clouds or cloud cores (q l > 0 and θ v > θ v ), where the overbar stands for domain average properties at each vertical level).…”