Observations of stratocumulus cloud break‐up over land

Detailed measurements were made during three episodes of boundary‐layer stratocumulus clouds occumng at Cardington, Bedfordshire, UK, using the UK Meteorological Oftice tethered‐balloon system. no cases were of cloud which dispersed or partly dispersed during the day, and the other was of persistent cloud. Analysis of these data reveals that one cloud deck dispersed owing to solar heating of the boundary layer warming the cloud above its dew‐point, and the other dispersed because of a combination of the above and entrainment of drier and warmer air into the top of the cloud caused by strong wind shear. This was the only incidence where entrainment was seen to affect significantly the morphology of a cloud deck. Data for the persistent case suggest that insufficient solar radiation penetrated into the boundary layer to cause significant warming and that the dynamics of the cloud were governed by radiative cooling at cloud top. the differences in the initial morphology of the cloud decks that caused them to evolve differently are discussed.