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An observational study of the structure of stratiform cloud sheets: Part I. Structure
Author(s) -
Nicholls S.,
Leighton J.
Publication year - 1986
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49711247209
Subject(s) - boundary layer , turbulence , cloud top , convective boundary layer , radiative transfer , atmospheric sciences , entrainment (biomusicology) , meteorology , environmental science , cloud computing , planetary boundary layer , convection , surface layer , geology , mechanics , physics , layer (electronics) , materials science , optics , computer science , rhythm , acoustics , composite material , operating system
Abstract Results from six flights with an instrumented aircraft in marine, stratiform cloud‐topped boundary layers are presented. The flights took place around the U.K. in a variety of conditions, both during the day and at night. The data comprise simultaneous, high resolution turbulence, cloud microphysics and radiation measurements. On five of the flights, turbulent mixing in the cloud layer was found to be primarily maintained by convection resulting from cloud top radiative cooling. In four cases, this mixed layer was observed to be decoupled from the surface, i.e. the cloud‐induced mixing did not extend down to the surface, and the cloud formed part of a detached turbulent layer. One flight in high surface wind conditions displayed a significantly different structure. Possible reasons for this are suggested. The mean microphysical features of the different cloud layers are compared, as are the measured and theoretically calculated radiation fluxes. The latter show good general agreement, but some systematic differences are apparent. Again, possible causes of these disparities are discussed. Features of the turbulent velocity field are presented and a number of similarities between data from the convective cases and cloud‐free boundary layers driven by heating from below are found. Values of the entrainment velocity are estimated directly from the measured cloud top water fluxes in all but one case, together with an estimate of the errors incurred. The measured vertical turbulent fluxes are found to be reasonably well predicted by diagnostic mixed‐layer models using the measured boundary conditions as long as the heights of the mixed‐layer boundaries are also specified from observations. Such a model is also used to help explain the main observed features of the mixed‐layer structure and the differences between the various cases.