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Radar Observations and Modelling of Warm Rain Initiation
Author(s) -
Caylor I. J.,
Illingworth A. J.
Publication year - 1987
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.49711347806
Subject(s) - drop (telecommunication) , liquid water content , radar , cloud physics , meteorology , cloud condensation nuclei , atmospheric sciences , physics , convection , computational physics , geology , cloud computing , environmental science , astrophysics , computer science , telecommunications , aerosol , operating system
Differential radar reflectivity data are presented which indicate that some initial echoes of convective clouds arise from a small number of very large raindrops; these raindrops may be supercooled. Typically raindrop concentrations are three orders of magnitude lower than the average Marshall‐Palmer drop size distribution found in mature clouds. an explanation of these observations in terms of the sweep‐out of cloud droplets by a low concentration of ultra‐giant nuclei of radii between 30 and 100 μm is offered. A simple model of this process, initiated using the average background levels of these nuclei, gives good agreement with the radar data. the model is not critically dependent upon the choice of collection efficiencies of the nuclei for the cloud droplets nor on the precise form of the ultra‐giant nucleus spectrum. the ultra‐giant nuclei seem capable of explaining the appearance of the raindrops without invoking complex mixing processes within clouds or appealing to the stochastic nature of the collisions between cloud droplets.