| D.W. Johnson, G.M. Martin and J.P. Taylor MRF Meteorological Office DRA Farnborough, Hants, England, GU14 6TD 252 24461 ext 5736 |
C.E. Friehe Department of Mechanical Engineering University of California, Irvine, CA 92717 |
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| D.P. Rogers Scripps Institution of Oceanography LaJolla, CA 92093-0230 | |||
The aerosol concentration in the boundary layer has a significant effect on the
microphysics and radiative properties of stratocumulus clouds. On the 15th and
16th June 1993, during the Atlantic Stratocumulus Transition Experiment
(ASTEX), a highly polluted air mass was advected off the European continent
towards the Azores. Observation from the UKMO Meteorological Research Flight's
C-130 aircraft on two flights on both these days will be presented. By flying
a large number of profiles it has been possible to produce a detailed picture
of the thermodynamic, dynamic and aerosol characteristics of the atmosphere
across the transition from the maritime to the continental air. Studies have
been made of the differences between the microphysics of the extensive sheets
of stratocumulus that were encountered in the two airmasses and the effects
this had on the radiative properties of these clouds. Distinct differences
were observed between the characteristics of the aerosol in and above the
boundary layer and model back trajectories have been used to try and understand
this. Some surprisingly large drizzle size droplets were found in the
continental clouds and possible mechanisms for producing these will be
discussed.