The dynamics of stratocumulus: Aircraft observations and comparisons with a mixed layer model

作者：S. Nicholls · 发表于：Quarterly Journal of the Royal Meteorological Society · 年份：1984 · DOI：10.1002/qj.49711046603 · 被引用次数：499 · 研究领域：Aeolian processes and effects、Atmospheric aerosols and clouds、Atmospheric chemistry and aerosols

Abstract Results are presented from a detailed case study of daytime stratocumulus over the North Sea using an instrumented aircraft. The measurements include turbulence fluctuation data, radiation fluxes and droplet spectra and were made both in and out of cloud. The mean structure is discussed and a diagnostic, one‐dimensional, mixed layer model is formulated to predict the variation of turbulent fluxes with height and to assess the sensitivity of these solutions to various physical processes. These predictions are compared with observations enabling the effectiveness of some widely used model assumptions to be tested. Water transport by gravitational settling is found to be important throughout the depth of the cloud. Mixing within the cloud is driven by convection generated primarily by radiative effects: strong cooling from cloud top with warming beneath although the net heating of the cloud layer is close to zero. Turbulent kinetic energy is exported downwards via negatively buoyant elements from the zone of intense cooling near cloud top into the body of the cloud. This appears to be achieved by the combined action of the turbulent transport and velocity‐pressure correlation terms in the turbulent kinetic energy balance equation which are therefore important in maintaining mixing in the lower part of the cloud. The cloud and sub‐cloud layers are found to be decoupled, i.e. they appear as two separated mixed layers. Reasons for this are examined and some further consequ...