In marine cumulus clouds, such as the trade wind cumuli studied during the RICO project, the situation is difficult for determining the entrainment sources and amounts. This is because the cloud layer within the marine boundary-layer is continuously recirculating; that is, the difference between clouds and their environment in cumulus clouds is relatively small. The situation is compounded by the fact that they contain very large amounts of liquid water. The implication is that temperature sensor wetting may be a significant effect and that thermodynamic tracers, Θq and Q, cannot in some cases be considered to be conservative due to the fallout of rain water.
In this study we examine 5 band clouds; for these we have measurements of thermodynamic tracers (Θq and Q), fast ozone and DMS. Preliminary results show that adiabatic or near-adiabatic cores do exist in the RICO cumulus clouds, although the main character of the cloudy air shows significant dilution with entrained air. Using thermodynamic tracers, the near adiabatic cores can only be identified by considering both cloud and rain water, and by using the Lyman-alpha hygrometers and assuming saturation in cloudy air. The chemical tracers show promise, but the difference between the ozone concentration between the mixed-layer air and the cloud-layer air is small. DMS measurements show some promise, but the signal is also affected by some noise.
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