Holes and Entrainment in Stratocumulus

• DOI: 10.1175/jas-3399.1
• Publication Date: 2005-03-03T21:50:39Z
• Authors: H. Gerber; G. Frick; S. P. Malinowski; J-L. Brenguier; F. Burnet
• Keywords: Entrainment (biomusicology); Marine stratocumulus; Liquid water content; Cloud height; Cloud top; Cloud fraction; Potential temperature; Diurnal cycle

Abstract Aircraft flights through stratocumulus clouds (Sc) during the Dynamics and Chemistry of Marine Stratocumulus II (DYCOMS-II) study off California coast found narrow in-cloud regions with less liquid water content (LWC) cooler temperatures than average background values. The are named cloud holes assumed to be a result evaporated by entrainment dryer air from above Sc. While such features have been noted previously, this provided unique opportunity investigate in much greater detail nature holes, as well their relationship rate, because high-speed temperature LWC probes maximum spatial resolution 10 cm were flown together for first time. Nine long-duration made mostly unbroken Sc which conditional sampling was used identify location size holes. concentrated near top, width top is about 5 m, relative length distribution nearly constant all flights, they can penetrate hundreds meters deep into before being lost mixing. Entrainment velocities at estimated measurements fluxes reduced vapor mixing ratios fraction area covered total jump between free atmosphere. Rates large mm s−1 nocturnal these rates 3 times larger daytime flight segments. correlate best buoyancy Sc; present conditional-sampling approach measuring gives “flux jump” determined others same factor 2. stability criterion predicts thinning breakup Sc, does not occur. minimal amount cloud-top evaporative cooling caused contributes little top-down convection dominated radiative flights; however, subduct large-scale eddy circulation may contribute, but an as-of-yet unknown amount.