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Journal Article

Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings


Ouwersloot,  H. G.
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Pietersen, H. P., Vilà-Guerau de Arellano, J., Augustin, P., van de Boer, A., de Coster, O., Delbarre, H., et al. (2015). Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings. Atmospheric Chemistry and Physics, 15(8), 4241-4257. doi:10.5194/acp-15-4241-2015.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0029-286F-7
We study the influence of the large-scale atmospheric contribution to the dynamics of the convective boundary layer (CBL) in a situation observed during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. We employ two modeling approaches, the mixed-layer theory and large-eddy simulation (LES), with a complete data set of surface and upper-air atmospheric observations, to quantify the contributions of the advection of heat and moisture, and subsidence. We find that by only taking surface and entrainment fluxes into account, the boundary-layer height is overestimated by 70 %. Constrained by surface and upper-air observations, we infer the large-scale vertical motions and horizontal advection of heat and moisture. Our findings show that subsidence has a clear diurnal pattern. Supported by the presence of a nearby mountain range, this pattern suggests that not only synoptic scales exert their influence on the boundary layer, but also mesoscale circulations. LES results show a satisfactory correspondence of the vertical structure of turbulent variables with observations. We also find that when large-scale advection and subsidence are included in the simulation, the values for turbulent kinetic energy are lower than without these large-scale forcings. We conclude that the prototypical CBL is a valid representation of the boundary-layer dynamics near regions characterized by complex topography and small-scale surface heterogeneity, provided that surface-and large-scale forcings are representative for the local boundary layer.