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Airborne studies of the altitudinal variability of the microphysical structure of small, ice‐free, montanan cumulus clouds
Author(s) -
Blyth Alan M.,
Latham John
Publication year - 1990
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.49711649608
Subject(s) - cloud base , atmospheric sciences , entrainment (biomusicology) , liquid water content , environmental science , cloud physics , ice crystals , altitude (triangle) , ice nucleus , adiabatic process , turbulence , mixing (physics) , lapse rate , effects of high altitude on humans , meteorology , physics , cloud computing , nucleation , thermodynamics , geometry , mathematics , quantum mechanics , rhythm , computer science , acoustics , operating system
The University of Wyoming's instrumented King Air aeroplane made special multiple‐altitude passes through seven non‐precipitating, essentially ice‐free summertime cumulus clouds, as part of CCOPE, conducted in Montana in 1981. The clouds were found to possess substantial microphysical variability on all detectable scales (down to 2 m) at all levels and distances from cloud boundaries. This was attributed to entrainment of environmental air, and evidence was found for a two‐stage process of turbulent mixing of cloudy and entrained air. Evaporation of the cloud drops was found to occur in a manner consistent with the ‘inhomogeneous mixing’ theory. Generally the clouds were negatively buoyant and more turbulent in the upper regions and in near equilibrium with the environment near cloud base. the normalized liquid water content was found to be roughly independent of altitude. Four of the clouds studied were found to contain embryonic raindrops (diameter 40 to 190 μm) in concentrations around 10 to 10001 −1 . Calculations and analysis showed that these particles could not have been formed in adiabatic clouds of the same base‐temperatures and depths, nor could they have been formed on ‘giant nuclei’. Their presence was shown to be explicable in terms of the ‘extreme inhomogeneous mixing’ model of accelerated growth. This mechanism also appears to offer an explanation for the small concentrations (≈0.1 m −3 ) of millimetric‐sized drops, shown in dual‐polarization studies often to be initiatory to substantial cloud development.