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Convective organization and its importance to large scale flows. Brian Mapes, U of Miami with Baohua Chen (UM) Richard Neale (NCAR) Emily Riley (UM). Organ-ization. From Greek organon about instrumentality or working order. "Organized" convection.

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convective organization and its importance to large scale flows

Convective organization and its importance to large scale flows

Brian Mapes, U of Miami

with

Baohua Chen (UM)

Richard Neale (NCAR)

Emily Riley (UM)

organ ization
Organ-ization
  • From Greek organon
    • about instrumentality or working order
organized convection
"Organized" convection
  • (weak) Something is making it patterned
    • perhaps it is forced or orchestrated
  • (too strong) It acts as an organ in an organism
    • it is performing some function
  • (agnostic) It is far from random in structure
    • has coherent (contiguous) entities
organized used many ways
Organized used many ways
  • multicellular (every cb is)
    • visual or radar
  • mesoscale patch or blob
    • or satellite 'cloud cluster'
  • line/arc structure as opposed to blobby
  • patchy on synoptic scale
a process view of organization
A process view of organization
  • In PDF language:
    • Extreme (tail) events in space of {w,T,q,scale,depth}
    • Vanishingly unlikely in naive multi-normal PDF
    • Taps an energy source, so natural selection acts
    • We can treat org as a positive effect
      • negative rare events (rogue gravity waves) are not reinforced in that way, and also not important
    • BUT: it doesn't mean optimal always happens
      • no wild eyed entropy extremal theorems here
effect of org on convection
effect of org. on convection
  • Thermo: protects penetrative updrafts from getting diluted by modal (mean or env.) air
  • Dyn: Assists in transfers/loans of energy to exploit metastability (triggered instability)
  • (Exotic momentum transport effects)
coherent structures
Coherent structures
  • may deserve separate treatment
  • like we add a 'plume' idealization for very asymmetric moist turbulence
  • multiplume / cooperating-plume structure an obvious generalization for org. convection
ls impacts of organization
LS impacts of organization?
  • Foreshadowing: one idea

"The Maritime Continent...presents a major challenge to models, which tend to systematically underestimate the precipitation in this region.

"It is argued that the diurnal cycle ... [and] ... circulation patterns generated by land–sea contrasts are crucial for ... the mean climate."

ls impacts of organization1
LS impacts of organization?
  • An observational view: use wide cloud systems as a working definition of organized

Emily Riley poster (2nd floor south end)

ls impacts of organization2
LS impacts of organization?
  • Observational backdrop: use wide cloud systems as a working definition of organized

Emily Riley poster (2nd floor south end)

ls impacts of organization3
LS impacts of organization?
  • Observational backdrop: use wide cloud systems as a working definition of organized

Exists beyond the margins of where unorganized (narrow) deep conv. can

Emily Riley poster (2nd floor south end)

ls impacts of organization4
LS impacts of organization
  • May be esp. important in convective margins like
    • upwind of deep tropics in the trades
      • e.g. in SE Pacific (Mar-Apr double ITCZ)
    • W African monsoon MCS dominated
    • western margin of Indian monsoon
  • Regions of GCM difficulties/biases?
gcms and organized convection
GCMs and organized convection
  • If org is what protects upflow from dilution, then GCMs deep convective plumes tuned to give a realistic stability have org everywhere
  • GCMs don't lack org, they lack its absence in deep convective onset situations
    • in the morning over land
    • in gradually moistening inflows to tropical rain
    • etc.
our experimental cam5 version
Our experimental CAM5 version
  • ZM deep convection turned off
  • Instead, 2 Park-Bretherton plumes
    • w/ different environmental mixing rates
  • Less-dilute plume's activity is an increasing function of organization W
  • Org. obeys: dW/dt = -W/t + Sources

Mapes and Neale 2011, JAMES

2 sources of organization w in our cam5 uw org ens version
2 Sources of Organization Win our CAM5-UW-org-ens version
  • Source1 is proportional to precip evaporation
  • Source2 >0 in coastal grid cells (optional)

JJA 0.25 degree

TRMM climo

results i effect of w feedback when it rains it organizes
Results I: Effect of W feedback (when it rains it organizes)

obs

deep convection

less dilute

W

gets us closer

Long-known tradeoff

"entrainment dilemma"

(Mapes and Neale 2011)

unstable mean state stable

more dilute

precip. variability 

results ii effect of coastal w source
Results II: Effect of coastal W source

Sense of result obvious

(more coastal rain)

What the heck??

slide22

Mystery is local to MC

Coastal W source everywhere but in MC

slide23

Mystery is local to MC

Coastal W source only in MC

why less mc rain with coastal w source
Why less MC rain with coastal W source?
  • more mass flux in plume #2...
slide25

...because Mean Sounding is drier and capped

Average in mysterious (less rain w/ coastal org)

MC region: 5S-10N, 90E-100E

slide26

... CIN > TKE

(closure)?

With Coast

10-days Hourly Data

Without Coast

10-days Hourly Data

slide27

...but Mean Sounding is drier so there is re-evap?

Average in mysterious (less rain w/ coastal org)

MC region: 5S-10N, 90E-100E

summary
Summary
  • Organized convection is coherent structures
  • Would be vanishingly rare in naive PDF view
  • Natural selection makes it common
  • Protects core updrafts in nature's deep convection
  • Standard GCM deep convection schemes imply org. is ubiquitous (not "missing")
  • Prognostic W created by rain evap (a positive feedback) helps w/ "entrainment dilemma"
      • (unwanted tradeoff btw. unstable bias  vs.  variability)
  • Coastal W source makes most coasts wetter, but core of Maritime continent drier (nonintuitive!)