OBSERVATIONS OF THE TURBULENT FLUXES IN FIELDS OF CUMULUS CLOUDS

Aircraft observations in fields of small maritime cumulus clouds aroun d the British Isles have been analysed to yield kinetic energy spectra and vertical turbulent fluxes, both within clouds and in the clear re gions between clouds, for five cases where a cool airmass flowed over a warmer sea surface. The flights were made at various times of the ye ar. Profiles of the kinetic energy and turbulent fluxes have been obta ined from observations made at several levels. It is shown that, while the dominant source of turbulent kinetic energy may be due to evapora tive cooling following entrainment at cloud top, in some cloud fields production by latent heating near cloud base dominates. The location o f the dominant energy source depends on whether the clouds penetrate t he inversion sufficiently for instability due to cloud-top entrainment to occur. While the resulting flux profiles observed in some of the c ases examined here resemble those observed in stratocumulus, profiles of similar shape are not always observed, End there are significant di fferences between cumulus layers and stratocumulus in the magnitudes o f the fluxes.