Cloud Shading Effects on Characteristic Boundary-Layer Length Scales

摘要: We studied the effects of shading by shallow cumulus (shallow Cu) and subsequent effect inducing heterogeneous conditions at surface on boundary-layer characteristics. placed special emphasis quantifying changes in characteristic length time scales associated with thermals, Cu induced thermal circulation structures. A series systematic numerical experiments, inspired Amazonian thermodynamic conditions, was performed using a large-eddy simulation model coupled to land-surface model. used four different experiments disentangle response clouds these changes. The include ‘clear case’, ‘transparent clouds’, ‘shading clouds’ case prescribed uniform domain reduced heat flux. also sensitivity study introducing weak background flow. Length were calculated autocorrelation two-dimensional spectral analysis, we found that controlled locally lowers temperatures consequently reduces sensible latent fluxes, thus spatial temporal variability fluxes. scale this heterogeneity is not sufficiently large generate circulations are superimposed scale, but does disturb dynamics generates flow opposite normal circulation. Besides effect, turbulent kinetic energy convective velocity reducing mass This hampers lifetime, resulting decrease residence (from 11 7 min). reduction combined flux, leads smaller clouds. partially compensated for cell size due energy. As result, inter-cloud distance reduced, leading larger population clouds, while maintaining cloud cover similar non-shading experiment. Introducing $$1\,\hbox {m}\, \hbox {s}^{-1}$$ wind speed increases sub-cloud layer, diagnosed surface–cloud coupling, quantified scales, remains.