Brian Mapes , University of Miami trying to be CAM-useful with much help from
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Using more than one plume to make GCM convective tendencies participate in large scale phenomena
better
Brian Mapes, University of Miami
trying to be CAM-usefulwith much help from
Rich Neale, Sungsu Park, Chris Bretherton, Julio Bacmeister
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Basis: well mixed steady plumes• Updraft mass flux is drawn from
the mean PBL » + perturbations ?
• Lateral mixing occurs instantly with the mean environment
» + perturbations ?
• Buoyancy determines how much mass starts & mixes, & where mixtures end up
• Tendencies built from vertical mass flux, microphysical processes, & any contingent downdrafts.
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Key claim to physical validity• Updraft mass flux is drawn from
the mean PBL » + perturbations ?
• Lateral mixing occurs instantly with the mean environment
» + perturbations ?
• Buoyancy determines how much mass starts & mixes, & where mixtures end up
• Tendencies built from vertical mass flux, microphysical processes, & any contingent downdrafts.
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Key uncertainty• Updraft mass flux is drawn from
the mean PBL » + perturbations ?
• Lateral mixing occurs instantly with the mean environment
» + perturbations ?
• Buoyancy determines how much mass starts & mixes, & where mixtures end up
• Tendencies built from vertical mass flux, microphysical processes, & any contingent downdrafts.
“The authors identify the entrainment rate coefficient of the
convection scheme as the most important single parameter...
[out of 31]...[for]...HadSM3 climate sensitivity”
Rougier et al. 2009, J.Clim.doi:10.1175/2008JCLI2533.1. (see Sanderson et al. 2010 too)
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Another big uncertainty: closure• Updraft mass flux is drawn from
the mean PBL » + perturbations ?
• Lateral mixing occurs instantly with the mean environment
» + perturbations ?
• Buoyancy determines how much mass starts & mixes, & where mixtures end up
• Tendencies built from vertical mass flux, microphysical processes, & any contingent downdrafts.
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1 plume type not enough?
Brooks Salzwedel Plume #1 2009 12" x 8” Mixed Media Plume #2 2009 12" x 8”
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Choice is self-fulfilling
Brooks Salzwedel Plume #1 2009 12" x 8” Mixed Media Plume #2 2009 12" x 8”
Smallentrainment
Deep, wideconvection
Largeentrainment
Shallow, narrow
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Can’t we have both?
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competing? favors the large
Tropical west Pacific mean sounding
requiring elaborate handicapping schemes
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more like a succession?
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precip organizes & enlarges plume bases
Khairoutdinov and Randall 2006
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?Time? well mixed steady plumes• Updraft mass flux is drawn from
the mean PBL » + perturbations ?
• Lateral mixing occurs instantly with the mean environment
» + perturbations ?
• Buoyancy determines how much mass starts & mixes, & where mixtures end up
• Tendencies built from vertical mass flux, microphysical processes, & any contingent downdrafts.
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Performance problem targets1. Entrainment dilemma (CCM2-CCM3, rehashed)– more mixing gives too-dilute convection
» unstable (e.g. cold aloft) climate biases
– less mixing gives too-undilute convection• weak q sensitivity
» too little variability, bland rainrate PDF, ...
– there is no “just right” in terms of constant ent. rate2. Closure issues (if separated from above)– variability, land/sea, SST/thermo/dyn sensitivities,...
3. Too instant response to instability• systematic: diurnal cycle over land• other variability surely affected
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What’s lacking?
lack = (nature) – (model)=
(convection’s subgrid variations in all fields and all systematic relationships among them)
-(independent mixing plumes rising from PBL in
uniform env.)
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Holistic parameterization
• Take the biggest possible bite of what’s missing, for minimum cost & arbitrariness
• Relationships, not just another subgrid thing
• Involves tails & ‘unlikely’ overlaps, cultivated by natural selection (penetrative buoyant ascent), not just slabs of gross macrophysics PDFs.
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Problems in knob space
1. plume base conditions and mixing effects are too situation-independent
2. Lack of finite-timescale development process
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Solutions in knob space
1. plume base conditions and mixing effects are too situation-independent
2. Lack of finite-timescale development process
suggests need for some prognostic measure of
subgrid convection “situation” to key off of
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‘Organization’
very much
very little
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‘Organization’
very much
very little
1. triggering
2. Non-average
updraft base air, in non-
average env.
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tests in 2 knob spaces (CAM, toy)
forced, t-damped
org(t)
A single prognostic variable: org(t)Connected to convection apparatus by adjustable
coefficients, so absolute value is meaningless.
t is a cloud system or cloud field timescale.t
A sum of N bubble-ascent time(s) S(Hi/wi) ? Maybe someday – for now just 3h.
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Full org treatment
forced, t-damped
org(t)Mb closure,
R .
local env
deeper,more rain
shear, rolls, deformation(directional?)
subgrid geog. Tb >
>Tmean + T’turb
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First CAM 3.5 expts (2007)
forced, 3-hour
damped
org(t)
local env
Mb trig, big R
Tb >
>Tmean + T’turb
ZM closure CAPE+
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org effects 1
• When it rains, it pours– rest of atm (mean) more stable
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org effects 2
• Delayed diurnal cycle
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(Offline) multi-Park/Breth plumes
forced, 3-hour
damped
org(t)
local env
Mb trig, big R
deeper,more rain
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Evading entrainment dilemma?
• deeper plumes will have moisture sensitivity indirectly, through their succession contingency on shallower ones
• without being too diluted
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Example: in COARE mean sounding, I get 8 plumes of increasing depth
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...but decreasing mass flux
Each contingent on the last for its gains
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Depends on org(a slider of plume overlap probability
between random (0) and maximum (1)
org = 0.5 org = 0.2
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Org effects
• Again: when it rains, it pours
• Mean state more stable, as convection occurs preferentially in org-enhanced microclimates
• stronger effect than latent heat of freezing on/off
• Delay time
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Plans for CAM
• Real Park-Bretherton plumes in real CAM
• Flexible implementation allowing various effects to be switched on/off
• learn our way around knob space» Biggy – plume radius/ ent. rate – appears still unavoidable
• Better diagnostics• falsifiable with CRM/LES data
» (not same as DERIVABLE FROM them!)