The Effects of Turbulent Mixing in Clouds

Baker, M.; Breidenthal, Robert E.; Choularton, T. W.; Latham, John

doi:10.1175/1520-0469(1984)041<0299:teotmi>2.0.co;2

Cited by 83 publications

(53 citation statements)

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“…This possibility can be countered by the high-resolution PVM data from the aircraft traverses through the Cu showing essentially no cloud-free voids except near cloud edges, and only showing small depleted LWC parcels with rounded edges further in the Cu. These observations can be related to the time scale given by τ mix = (D 2 /ε) 1/3 (Baker et al 1984) for complete homogenization of entrained parcels with the rest of the cloud. For example, given a parcel dimen- sion of D = 2 m, and using a mean value of ε from Fig.…”

Section: Scales Of Entrained Parcelsmentioning

confidence: 99%

Entrainment, Mixing, and Microphysics in Trade-Wind Cumulus

Gerber

Frick

Jensen

et al. 2008

Journal of the Meteorological Society of Japan

180

236

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The vertical evolution of microphysics in trade-wind cumuli (Cu) observed from the NCAR C-130 research aircraft during one flight of the RICO (Rain in Cumulus Over the Ocean) study is analyzed. Conditional sampling of > 200 Cu traversed on this flight is used to chose Cu for which the aircraft penetrated single and growing Cu turrets about 250-m below cloud top where maximum LWC is often found and where radar has often observed initial stages of precipitation. The vertical evolution of the sampled set of Cu was assumed to follow Lagrangian behavior. The entrainment rate, entrained parcel scales, mixing mechanisms, and effects on the droplet size distribution are measured and evaluated. A parcel model is applied over the 1100-m maximum Cu height of the traverses to determine the relationship between the observed large number of small droplets and the fewer ultra-giant sea-salt nuclei (UGN) in order to assess the role of these nuclei in evolving the size spectrum and in causing a growing "drizzle tail". New insight on these topics is obtained by using the PVM (Particle Volume Monitor) probe to measure incloud microphysics with 10-cm resolution.The results include the following: Entrainment causes primarily dilution of the drops without significant size changes, thus either extreme inhomogeneous mixing or more likely homogeneous mixing resulting from mixing with cool and humid entrained air take place. The entrained parcels are surprisingly small following lognormal behavior and decaying rapidly upon entering the Cu, as a result super-adiabatic drops are not evident. The entrained parcels are consistent with the Bragg-scattering "mantle echo" often observed by radar in small Cu. The FSSP (Forward Scattering Spectrometer Probe) droplet spectra are nearly constant with height. These "self-preserving" spectra are a result of an approximate balance between dilution by entrainment of droplets originating at cloud base, droplet activation on entrained CCN (cloud condensation nuclei), and detrainment and coalescence losses. Sea-salt nuclei follow Woodcock's wind dependence, and are shown with the parcel model to play an important role in forming the observed drizzle that increases with cloud height. Accretion is the dominant coalescence mechanism near cloud top in these Cu.

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Section: Scales Of Entrained Parcelsmentioning

confidence: 99%

Entrainment, Mixing, and Microphysics in Trade-Wind Cumulus

Gerber

Frick

Jensen

et al. 2008

Journal of the Meteorological Society of Japan

180

236

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“…t evap whereby drops adjacent to sub-saturated regions completely evaporate rapidly while the remaining drops are completely unaffected. Following Baker et al (1984), the time scale for the evaporation of a single drop is given by:…”

Section: Introductionmentioning

confidence: 99%

“…During inhomogeneous mixing, a subset of drops completely evaporates to re-establish saturation, causing N to decrease, but the shape of the DSD remains the same. The ratio of the time scale it takes for a drop to evaporate, t evap , to the time scale required to mix the cloudy and cloud-free air, t mix (Baker et al, 1984), is believed to control the cloud microphysical response to entrainment, that is, the location in the continuum between homogeneous and inhomogeneous mixing. In the limit, homogeneous mixing occurs when t evap !!…”

Section: Introductionmentioning

confidence: 99%

Microphysical imprint of entrainment in warm cumulus

Griswold

Chuang

Jonsson

2013

Tellus B: Chemical and Physical Meteorology

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A B S T R A C TWe analyse the cloud microphysical response to entrainment mixing in warm cumulus clouds observed from the CIRPAS Twin Otter during the GoMACCS field campaign near Houston, Texas, in summer 2006. Cloud drop size distributions and cloud liquid water contents from the Artium Flight phase-Doppler interferometer in conjunction with meteorological observations are used to investigate the degree to which inhomogeneous versus homogeneous mixing is preferred as a function of height above cloud base, distance from cloud edge and aerosol concentration. Using four complete days of data with 101 cloud penetrations (minimum 300 m in length), we find that inhomogeneous mixing primarily explains liquid water variability in these clouds. Furthermore, we show that there is a tendency for mixing to be more homogeneous towards the cloud top, which we attribute to the combination of increased turbulent kinetic energy and cloud drop size with altitude which together cause the Damko¨hler number to increase by a factor of between 10 and 30 from cloud base to cloud top. We also find that cloud edges appear to be air from cloud centres that have been diluted solely through inhomogeneous mixing. Theory predicts the potential for aerosol to affect mixing type via changes in drop size over the range of aerosol concentrations experienced (moderately polluted rural sites to highly polluted urban sites). However, the observations, while consistent with this hypothesis, do not show a statistically significant effect of aerosol on mixing type.

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“…This is likely due to secondary activation of droplets during entrainment and will be discussed in the following section. discuss that possibility (Baker et al 1984;Andrejczuk et al 2004).…”

mentioning

confidence: 96%