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IntroductionEntrainment
Edges of cloudsSummary
Entrainment and Mixing in Cumulus Clouds
Alan Blyth
NCAS, University of Leeds
25 March 2009
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
OutlineCloud microphysics
Outline
Alan Blyth Entrainment and Mixing in Cumulus Clouds
Cumulus clouds
Start Movie
IntroductionEntrainment
Edges of cloudsSummary
OutlineCloud microphysics
Liquid water content
From: Warner (1955) Raga et al (1990)
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
OutlineCloud microphysics
From: Blyth and Latham 1990
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
OutlineCloud microphysics
Liquid water content
Trade-wind cumulus clouds 2005
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
OutlineCloud microphysics
LWC - COPS
COPS cumulus clouds, 15 July 2007. Justin Peter
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
OutlineCloud microphysics
Concentration (N) and mean diameter (d)
Trade-wind cumulus clouds 2005
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Entrainment
Two scales:
Cloud scale - where does entrainment occur and whathappens to entrained air?Small scale at boundaries - what is the mechanism for airexchange across boundaries?
Alan Blyth Entrainment and Mixing in Cumulus Clouds
Plumes, Thermals and Starting Plumes
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Entrainment in Plume
Expect entrained air from below
Alan Blyth Entrainment and Mixing in Cumulus Clouds
Thermals
From: Woodward 1959Expect entrained air from above and below
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Thermodynamic arguments
Use thermodynamic tracers in cloud - conserved variables
Use θq and Q (Paluch 1979). Invariant in adiabatic altitudechanges and mix linearly.
θq = T(
1000pd
)(Rd /Cp)/[1+Cw /Cpd Q]
× exp[
qLCpdT
/
(1 +
CwCpd
Q)]
and
Q = qv + ql
Alan Blyth Entrainment and Mixing in Cumulus Clouds
From Paluch 1979
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
From: Blyth et al. 1988
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Taylor and Baker
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Taylor and Baker
Distribution of points on Paluch diagram does notnecessarily mean ascent of adiabatic parcel followed bymixing – same distribution if mixing occurs continuously asparcel ascends as long as +vely buoyant.Different from Raymond and Blyth
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Wang and Geerts: cooling of reverse flow temperature probe
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Wang and Geerts
“The EC [evaporative cooling] correction proposed hereinshould be applied to all those studies. Since most of themeasurements in the papers listed above occurred attemperatures above -12C, their analyses are affected andsome of their conclusions may be flawed.”
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Downdrafts
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Observations of Thermals
From: Blyth et al, 1988
Alan Blyth Entrainment and Mixing in Cumulus Clouds
19 July 1981, CCOPE, Montana: 1625 - 1633
July, 1995, SCMS, Florida
Damiani et al
Damiani et al
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Damiani et al
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Damiani et al
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Schematic picture of thermals and entrainment
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Erosion of the core
Alan Blyth Entrainment and Mixing in Cumulus Clouds
Reduced LWC in middle of updraft
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Drop size distribution in the hole
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Cloud models: Richard Carpenter
From Carpenter et al (1990)
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Model of Cu cloud showing thermal
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Model of Cu cloud showing thermal
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Model of Cu cloud showing thermal
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Model of Cu cloud showing thermal
Alan Blyth Entrainment and Mixing in Cumulus Clouds
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
How clouds entrain
Courtesy of Dr. Sonia Lasher-Trapp
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Heus et al: Modelling results
“The obtained Paluch diagrams are found to be similar to manyresults in the literature, but the source of entrained air found byparticle tracking deviates from the source inferred from the Paluchanalysis.Whereas the classical Paluch analysis seems to provide someevidence for cloud-top mixing, particle tracking shows that virtually allmixing occurs laterally.Particle trajectories averaged over the entire cloud ensemble alsoclearly indicate the absence of significant cloud-top mixing in shallowcumulus clouds.”
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Plumes and thermalsObservations of source of entrained airThermalsModelling of Clouds
Heus et al
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
What happens at the boundaries?
From Baker et al. (1984)
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
From Jensen and Baker (1989)
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
Cloud edges
The sharpness of cloud edges must tell us somethingabout the relative magnitudes of the processesstrengthening and weakening the gradients thereGradients are sharpened due to buoyancy and smoothedout due to turbulent eddies
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
Gradients in LWC and vertical wind; convergence
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
Does this happen at the edges of Clouds?
From Grabowski and Clark (1993)
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
Heus and Jonkers: cloud-edge downdrafts
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
Heus and Jonkers, 2003
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Cloud Boundaries
Schematic of cloud with descending shell
Rodts et al., 2003
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Summary
Does entrainment occur at ascending cloud top?
Not the edges of thermalAt rear of thermal
Some model results suggest lateral entrainment?Thermals important for circulating the entrained air downthe edges and into centreDilution of thermal about 3-5 mins?How long for molecular mixing vs bulk transportNeed improved in-cloud temperature probes to makeprogress
Alan Blyth Entrainment and Mixing in Cumulus Clouds
IntroductionEntrainment
Edges of cloudsSummary
Acknowledgements
Many thanks to:William Cooper, Sonia Lasher-Trapp and JorgenJensen,
Alan Blyth Entrainment and Mixing in Cumulus Clouds