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要旨

This study investigates the interplay between atmospheric moisture and deep convective clouds via cold-pool dynamics in the absence of large-scale forcing in a series of cloud-resolving modelling studies. More specifically, the contribution of moisture advection, evaporation of rain and surface fluxes to the moisture budget over particular regions of the domain is investigated. This is done both for a continental case and an oceanic case although both cases show very similar behaviour. The accumulation of moisture in confined regions of the sub-cloud layer that constitute preferred locations for future cloud development mainly results from the advection of moisture. The latter contributes ~86%, minor evaporation of precipitation contributes ~4%, whereas surface moisture fluxes yield ~11% in the continental case. In the oceanic case advection contributes ~125%, surface moisture fluxes ~-32% and evaporation of precipitation ~7%. To further identify the origin of the advected moisture, additional scalars marking moisture originating from the surface and from the evaporation of rain are introduced into the model. It is seen that the surface moisture and the evaporated rain water released within the last 2 h only make 55% of the moisture accumulated in the moist patches in the land case, the rest stemming from older moisture. In the ocean case, this share increases to 72%. The contribution of recently released moisture drops to 28% at cloud base in the continental case and to 56% in the ocean case. The contribution at cloud base is dominated by surface fluxes; the evaporation of rain is negligible. © 2015 Royal Meteorological Society.